Spontaneous regression of a hepatoma with ring calcification.

The authors report a 74-year-old man with chronic hepatitis C-related cirrhosis and end-stage renal disease undergoing maintenance haemodialysis who was diagnosed with hepatoma. The hepatoma spontaneously regressed with significantly decreased serum alpha-fetoprotein level without any treatment during the subsequent 4-year follow-up period. However, recurrent hepatomas over bilateral hepatic lobes were evident thereafter, and the patient died later due to hepatic failure. Hepatoma with ring calcification is extremely rare and considered poor differentiation with high risk for recurrence. Spontaneous regression of hepatoma is also rare, while spontaneous regression occurring in a hepatoma with ring calcification is never reported. The definite mechanisms causing spontaneous regression of hepatomas remain unclear, but an immune response toward hepatoma induced by alpha-fetoprotein might play an important role.

Classification and treatment of pooling of contrast material on computed tomographic scan of blunt hepatic trauma.

BACKGROUND: Pooling of contrast material on computed tomographic (CT) scan represents free extravasation of blood as a result of active bleeding. For patients with blunt hepatic injury, aggressive management such as angiography or celiotomy is usually indicated if this sign is detected. The purposes of this study were to further categorize this CT scan finding and to correlate its characteristics with clinical outcomes. This CT scan classification might be helpful for the selection of appropriate management. METHODS: During a 42-month period, 276 patients with blunt hepatic injury were treated. Two hundred twelve of them were hemodynamically stable after initial resuscitation and underwent abdominal CT scan examination. Pooling of contrast material was detected on the CT scans of 15 patients. The CT scans and medical records were reviewed. Special attention was paid to the presence, location, and character of the extravasated contrast material. RESULTS: The finding of pooling of contrast material on CT scan was categorized into three types according to its location and character. Type I showed extravasation and pooling of contrast material in the peritoneal cavity (six patients). All patients with type I CT scan findings became hemodynamically unstable soon after CT scan examination and required emergent laparotomy. Type II findings showed simultaneous presence of hemoperitoneum and intraparenchymal contrast material pooling (six patients). Four patients with type II CT scan findings required laparotomy for hemostasis. Type III findings showed intraparenchymal contrast material pooling without hemoperitoneum (three patients). All patients with type III CT scan signs remained hemodynamically stable. CONCLUSION: With the use of a high-speed spiral CT scanner, it is possible to predict the necessity of operative management or angiography for patients with blunt hepatic injury before deterioration of hemodynamic status. The presence of pooling of contrast material within the peritoneal cavity indicates active and massive bleeding. Patients with this CT scan finding show rapid deterioration of hemodynamic status. Most of these patients might require emergent surgery. Pooling of contrast material in a ruptured hepatic parenchyma indicates active bleeding. Close monitoring and emergent angiography should be performed. Deterioration of hemodynamic status in these patients usually requires prompt surgical intervention. Intraparenchymal pooling of contrast material with unruptured liver capsule often indicates a self-limited hemorrhage. Patients with this CT scan finding have a high possibility of successful nonoperative treatment.

Factors determining operative mortality of grade V blunt hepatic trauma.

BACKGROUND: Despite recent advances in the management of severe hepatic injuries, the operative mortality rate of grade V hepatic injuries still ranges from 67% to 80%. Grade V hepatic injuries involving the retrohepatic cava or main hepatic veins are almost always lethal, especially those from blunt trauma. The purpose of this study is to understand the risk factors determining operative mortality in grade V blunt hepatic trauma, and to try to improve the surgical management of these injuries. METHODS: A retrospective study was conducted at a medical center that offers services including primary, secondary, and tertiary care. Forty-four patients with grade V blunt hepatic injuries were treated during a 6-year period from January 1, 1991, to December 31, 1996. The operative mortality was compared by a multivariate analysis. RESULTS: Forty-four patients with grade V blunt hepatic injuries were identified. Seven patients had only parenchymal injuries, and the others had vascular and associated parenchymal injuries. Venorrhaphy was used in 37 patients; 29 were treated using a nonshunting approach, and 8 with an atriocaval shunt. The overall mortality rate was 68% (30 of 44), and liver-related mortality was 50% (22 of 44). Univariate analysis revealed that the significant variables affecting operative mortality were initial systolic blood pressure, initial base deficit, the Glasgow Coma Scale, injury type, number of resected segments, and total intraoperative blood loss. Based on forward stepping logistic regression analysis, patients with an initial base deficit of -6 mmol/L or less (relative risk = 17.3), and a total intraoperative blood loss of 5,000 mL or more (relative risk = 23.5) would, significantly, encounter a worsening prognosis. CONCLUSIONS: Initial base deficit and total intraoperative blood loss were the significant factors that determined operative mortality after grade V blunt hepatic trauma. We suggest that prompt resuscitation and expeditious and appropriate surgical management, to control operative blood loss, is the only way to reduce operative mortality in patients with grade V blunt hepatic trauma.

Blunt hepatic injury: minimal intervention is the policy of treatment.

BACKGROUND: Many publications recommend nonoperative treatment for stable blunt hepatic injury patients. Unstable hemodynamic status is the only indication for surgery. When operation is indicated, controversies exist regarding which operative procedure will be more beneficial to the patients. The purposes of this study are to compare the results of operative and nonoperative management of patients with blunt hepatic injuries and to identify the optimal surgical approach when surgery is indicated. METHODS: Different prospective protocols of treating adult blunt hepatic injuries were conducted. From 1992 to 1993 (group I), urgent surgery would be performed in the presence of hemoperitoneum. The policy shifted to aggressive nonoperative approach between 1996 and 1997 (group II). The patients from each period were divided into three subgroups. Group A included the patients who received nonoperative treatment in either period. Group B consisted of the patients who received surgery in the first period and nonoperative management in the second period. Group C included the patients who were operated on in either group. Comparisons were made between matched groups. RESULTS: Groups IA and IIA patients had minor injuries and could be successfully treated nonoperatively. The results of groups IB and IIB were similar concerning hospital stay, morbidity, and mortality. Transfusion requirements of group IIB patients were significantly higher (2.2 vs. 1.1 units,p = 0.01) than those of group IB. However, 25 (58%) celiotomies of group IB patients were nontherapeutic. When surgery was indicated, group IC patients had significantly higher liver-related mortality (14 of 49 vs. 3 of 55, p = 0.002). Anatomic resection was performed more frequently in that period. CONCLUSION: Nonoperative treatment significantly decreased the rate of nontherapeutic laparotomy but carried the risks of higher transfusion requirements and delaying operation. When surgery was indicated, the policy of minimal intervention positively affected the patients' outcomes. The goal of surgery should be hemorrhage control rather than resection of the injured liver tissues.

Binding of retinol induces changes in rat cellular retinol-binding protein II conformation and backbone dynamics.

The structure and backbone dynamics of rat holo cellular retinol-binding protein II (holo-CRBP II) in solution has been determined by multidimensional NMR. The final structure ensemble was based on 3980 distance and 30 dihedral angle restraints, and was calculated using metric matrix distance geometry with pairwise Gaussian metrization followed by simulated annealing. The average RMS deviation of the backbone atoms for the final 25 structures relative to their mean coordinates is 0.85(+/-0.09) A. Comparison of the solution structure of holo-CRBP II with apo-CRBP II indicates that the protein undergoes conformational changes not previously observed in crystalline CRBP II, affecting residues 28-35 of the helix-turn-helix, residues 37-38 of the subsequent linker, as well as the beta-hairpin C-D, E-F and G-H loops. The bound retinol is completely buried inside the binding cavity and oriented as in the crystal structure. The order parameters derived from the (15)N T(1), T(2) and steady-state NOE parameters show that the backbone dynamics of holo-CRBP II is restricted throughout the polypeptide. The T(2) derived apparent backbone exchange rate and amide (1)H exchange rate both indicate that the microsecond to second timescale conformational exchange occurring in the portal region of the apo form has been suppressed in the holo form.

Laparoscopic decompression of abdominal compartment syndrome after blunt hepatic trauma.

Abdominal compartment syndrome (ACS) can occur in a variety of surgical conditions, particularly those with major life-threatening hemorrhage, massive volume resuscitation, prolonged operation times, and coagulopathy. In severely traumatized patients, the incidence of ACS is reported to be as high as 14% to 15% after damage control laparotomies. Although favorable results have been achieved with nonsurgical management of adult blunt hepatic trauma, the failure rates still range from 0% to 19%. Exploratory laparotomy is considered the intervention of choice in patients with blunt hepatic trauma who fail nonsurgical treatment. Expedient abdominal decompression currently is the treatment of choice after ACS. Oliguria, tachypnea, and tachycardia developed in two blunt hepatic trauma patients with grade IV and V injuries while they were receiving nonsurgical treatment. The intra-abdominal pressures measured more than 35 and 25 cm H 2O, respectively. Two patients with grade II and III ACS received laparoscopic examination instead of laparotomy. Their ACS was decompressed effectively via laparoscopy without any adverse effects. Therefore, we suggest that laparoscopy can be used as a safe alternative for the decompression of ACS.

Prognosis in presumptive hypoxic-ischemic coma in nonneurologic trauma.

BACKGROUND: The neurologic outcome of comatose patients has a wide variation from complete reawakening to death. Methods of predicting the outcome of coma caused by either head injury or cardiac arrest have been the subject of much discussion in the literature. However, prediction of neurologic prognosis in comatose trauma patients without head injury has rarely been discussed. We reviewed our experience in treating patients with presumptive hypoxic-ischemic coma after trauma and tried to identify factors relating to their neurologic outcomes. METHODS: Thirty-six patients with normal brain computed tomographic scans, who remained comatose 10 minutes after stabilization of their hemodynamic status, were studied. Serial motor response, verbal response, pupillary light reflex, presence of spontaneous breathing and seizure, and blood glucose level were recorded to evaluate their roles in predicting neurologic outcomes. RESULTS: There were five deaths (mortality rate, 14%) and 11 patients (31%) with neurologic deficits. An absence of spontaneous breathing, a blood glucose level greater than 300 mg/dL during resuscitation, and a presence of seizure signified a poor prognosis. Initial neurologic evaluation at 10 minutes after stabilization of hemodynamic status was not accurate in predicting outcome. A motor response worse than withdrawal from painful stimuli at 24 hours after injury and an absence of pupillary light reflex at 48 hours after injury predicted a poor neurologic outcome, with a 100% accuracy rate. CONCLUSION: Hypoxic-ischemic coma in patients sustaining major trauma yielded a significantly better survival and neurologic outcome than that induced by cardiac arrest or head injury. Decision-making in the first 24 hours after injury should not be affected by the patient's neurologic status at that time. A motor response worse than withdrawal at 24 hours after injury and an absence of pupillary light reflex at 48 hours after injury predicted a poor neurologic outcome.

Small bowel perforation: is urgent surgery necessary?

BACKGROUND: Controversies regarding how urgent bowel perforation should be diagnosed and treated exist in recent reports. The approach for early diagnosis is also debatable. The purposes of this study were to evaluate the relationship between treatment delay and outcome of small bowel perforation after blunt abdominal trauma and to determine the best assessment plan for the diagnosis of this injury. METHODS: One hundred eleven consecutive patients with small bowel perforations caused by blunt abdominal trauma were retrospectively reviewed. The patients were divided into four groups according to the time interval between injury and surgery. Hospital stay, time to resume oral intake, and mortality and morbidity rates were compared between groups. Physical signs, laboratory and computed tomographic findings, and the results of diagnostic peritoneal lavage were analyzed to find the most sensitive and specific test for early diagnosis of small bowel perforation. RESULTS: Delay in surgery for more than 24 hours did not significantly increase the mortality with modern method of treatment; however, complications increased dramatically. Hospital stay and time to resume oral intake increased significantly when surgery was delayed for more than 24 hours. Abdominal tenderness was a common finding, but it was not specific for bowel perforation. Only 40% of the computed tomographic scans were diagnostic for bowel perforations: 50% of them showed suggestive signs, and 10% were considered as negative. Persistence of abdominal signs indicated peritoneal lavage. By using cell count ratio in diagnostic peritoneal lavage and/or increased lavage amylase activity, presence of particulate matter and/or bacteria in the lavage fluid, all patients with intraperitoneal bowel perforation were diagnosed accurately before operation. CONCLUSION: Small bowel perforation has low mortality and complication rates if it is treated earlier than 24 hours after injury. The principle of "rushing to the operation suite" for a stable blunt abdominal trauma patients without detailed systemic examination is not justified. The priority of treatment for the small bowel perforation should be lower than the limb-threatening injuries. Diagnostic peritoneal lavage provides high sensitivity and specificity rates for the diagnosis of small bowel perforation if a specially designed positive criterion is applied.

Retroperitoneal laparostomy: an effective treatment of extensive intractable retroperitoneal abscess after blunt duodenal trauma.

BACKGROUND: Delay in surgical treatment and duodenal wound dehiscence are two major causes of extensive retroperitoneal abscess formation after blunt duodenal injury. This complication is traditionally treated with primary repair of the duodenal wound and drainage of the abscess through anterior laparotomy. Pyloric exclusion is sometimes added as an adjunctive procedure. The anterior approach, however, may result in inadequate drainage, and repeat surgery is sometimes needed. We reviewed our experiences and evaluated the effectiveness of retroperitoneal laparostomy for the treatment of retroperitoneal abscess with continuous soiling. METHODS: There were 52 blunt duodenal injuries during a 7-year period. Eleven patients developed extensive retroperitoneal abscesses. RESULTS: All 11 patients were treated with anterior laparotomy initially. Five patients recovered after this procedure. Six patients continued to have retroperitoneal abscesses and were under septic status. Two patients received another anterior drainage, and had recurrent abscesses later. Retroperitoneal laparostomy was performed for these six patients. After retroperitoneal laparostomy, daily wound care, and antibiotic treatment, all six patients recovered. Only two patients developed incisional hernia. CONCLUSION: Retroperitoneal laparostomy is effective in treating extensive intractable retroperitoneal abscess after blunt duodenal injury. Patients with the complications of duodenal leak and extensive retroperitoneal abscess should be treated with pyloric exclusion and drainage through anterior laparotomy first. If the duodenal wound does not heal after pyloric exclusion and retroperitoneal abscess persists, retroperitoneal laparostomy should be performed without further attempt to repair the wound.

The structure and dynamics of rat apo-cellular retinol-binding protein II in solution: comparison with the X-ray structure.

The structure and dynamics of rat apo-cellular retinol binding protein II (apo-CRBP II) in solution has been determined by multidimensional NMR analysis of uniformly enriched recombinant rat 13C, 15N-apo-CRBP II and 15N-apo-CRBP II. The final ensemble of 24 NMR structures has been calculated from 3274 conformational restraints or 24.4 restraints/residue. The average root-mean-square deviation of the backbone atoms for the final 24 structures relative to their mean structure is 1.06 A. Although the average solution structure is very similar to the crystal structure, it differs at the putative entrance to the binding cavity, which is formed by the helix-turn-helix motif, the betaC-betaD turn and the betaE-betaF turn. The mean coordinates of the main-chain atoms of amino acid residues 28-38 are displaced in the solution structure relative to the crystal structure. The side-chain of F58, located on the betaC-betaD turn, is reoriented such that it interacts with L37 and no longer blocks entry into the ligand-binding pocket. Residues 28-35, which form the second helix of the helix-turn-helix motif in the crystal structure, do not exhibit a helical conformation in the solution structure. The solution structure of apo-CRBP II exhibits discrete regions of backbone disorder which are most pronounced at residues 28-32, 37-38 and 73-76 in the betaE-betaF turn as evaluated by the consensus chemical shift index, the root-mean-square deviation, amide 1H exchange rates and 15N relaxation studies. These studies indicate that fluctuations in protein conformation occur on the microseconds to ms time-scale in these regions of the protein. Some of these exchange processes can be directly observed in the three-dimensional 15N-resolved NOESY spectrum. These results suggest that in solution, apo-CRBP II undergoes conformational changes on the microseconds to ms time-scale which result in increased access to the binding cavity.

Pooling of contrast material on computed tomography mandates aggressive management of blunt hepatic injury.

BACKGROUND: Nonoperative management of blunt hepatic injury is currently a widely accepted treatment modality. Computed tomography (CT) is an important imaging study both for diagnosis and follow-up of these patients. There is, however, no reliable predictor of failure of nonoperative treatment other than the ultimate development of hemodynamic instability. Previous reports mostly were based on the data obtained from low-speed dynamic incremental scanners. The purpose of this study is to evaluate the value of a high-speed helical scanner in predicting the outcome of patients managed nonoperatively. METHODS: During a 30-month period, 194 patients with blunt hepatic injury were treated, 150 of them were hemodynamically stable after initial resuscitation and underwent abdominal CT examination. All CT scans were performed with the High Speed Advantage Scanner. The CT scans and medical records were reviewed. RESULTS: Nonoperative management was successfully applied to all patients with grade I and II, 93% of grade III, 87% of grade IV, and 67% of grade V liver injuries. Twelve patients required liver-related celiotomy. Pooling of contrast material was detected on the CT scans of 8 patients. Six (75%) of these patients developed hemodynamic instability and required liver-related celiotomy later. Pooling of contrast material can be detected in 50% of the patients receiving liver-related celiotomy. CONCLUSION: The presence of pooling of contrast material within the hepatic parenchyma indicates free extravasation of blood as a result of active bleeding. In patients with blunt hepatic injury, if this sign is detected, nonoperative treatment should be terminated and angiography or celiotomy undertaken promptly. With the increasing use of high-speed spiral CT scanner and improvement in scanning technique, pooling of contrast material may become a sensitive sign for active bleeding and may be used as a guide for the selection of treatment modality.

Malakoplakia of the mesocolon with gastric serosa invasion: a case report and review of the literature.

Malakoplakia is a rare, granulomatous, inflammatory disease. The clinical presentation and radiological appearance of the malakoplakia mimics a malignant tumor. In this article we describe a case of the malakoplakia of the mesocolon with invasion into the serosa of the stomach. The frozen section report considered the lesion to be a malignancy. The definitive diagnosis depended on microscopic detection of Michaelis-Gutmann bodies by electronic microscope. We review the current literature about the malakoplakia of gastrointestinal tract, and focus on the pathogenesis, clinical manifestation, diagnosis and treatment.

Selective application of laparoscopy and fibrin glue in the failure of nonoperative management of blunt hepatic trauma.

BACKGROUND: Most blunt hepatic trauma patients can be managed nonoperatively. The current failure rate in adult blunt hepatic trauma is reportedly 0 to 19%. We wished to evaluate the applicability of laparoscopy and fibrin glue as a minimally invasive alternative to laparotomy in these unsuccessfully nonoperative cases. METHODS: All adult patients with blunt hepatic trauma managed nonoperatively at Linkou, Chang Gung Memorial Hospital Medical Center, Taipei, Taiwan, over a 2-year period from July 1, 1994, to June 30, 1996, were eligible for the study. A laparoscopic examination was performed on those who failed conservative care before undertaking an exploratory laparotomy. Fibrin glue was sprayed over the wound surface if ongoing hemorrhage was evident from any liver laceration. The clinical data, operative and laparoscopic findings, operative methods, and outcomes of these patients were studied. RESULTS: Of the 61 patients, 55 patients were successfully treated without operation. Of the six failures (10%) all were liver related. After the introduction of laparoscopy, the nontherapeutic laparotomy rate would have decreased from 100% (6 of 6) to 50% (3 of 6), and with the adjunctive use of fibrin glue, the laparotomy rate went down to 0% (0 of 6). There were no deaths among the six patients receiving laparoscopy and fibrin glues; and only one developed a liver abscess, for a morbidity rate of 17% (1 of 6). CONCLUSIONS: The selective use of laparoscopy and fibrin glue can effectively reduce the nontherapeutic laparotomy rate among blunt hepatic trauma patients who fail nonoperative management.

The structure of d(TpA), the major photoproduct of thymidylyl-(3'5')-deoxyadenosine.

Irradiation of the dinucleotide TpdA and TA-containing oligonucleotides and DNA produces the TA* photoproduct which was proposed to be the [2+2] cyclo-addition adduct between the C5-C6 double bonds of the T and the A [Bose,S.N., Kumar,S., Davies,R.J.H., Sethi,S.K. and McCloskey,J.A. (1984) Nucleic Acids Res. 12, 7929-7947]. The proposed structure was based on a variety of spectroscopic and chemical degradation studies, and the assignment of a trans-syn-I stereochemistry was based on an extensive 1H-NMR and molecular modeling study of the dinucleotide adduct [Koning,T.M.G., Davies,R.J.H. and Kaptein,R. (1990) Nucleic Acids Res. 18, 277-284]. However, a number of properties of TA* are not in accord with the originally proposed structure, and prompted a re-evaluation of the structure. To assign the 13C spectrum and establish the bond connectivities of the TA* photoproduct of TpdA [d(TpA)*], 1H-13C heteronuclear multiple-quantum coherence (HMQC) and heteronuclear multiple bond correlation (HMBC) spectra were obtained. The 13C shifts and connectivities were found to be inconsistent with the originally proposed cyclobutane ring fusion between the thymine and adenine, but could be explained by a subsequent ring-expansion reaction to give an eight-membered ring valence isomer. The new structure for the d(TpA)* resolves the inconsistencies with the originally proposed structure, and could have a stereochemistry that arises from the anti, anti glycosyl conformation found in B form DNA.

Conformational mimicry: synthesis and solution conformation of a cyclic somatostatin hexapeptide containing a tetrazole cis amide bond surrogate.

Potent, cyclic hexapeptide analogues of somatostatin are generally believed to adopt some common secondary structural features: a II' beta turn at one end of the cycle, and a type VI turn with a cis amide bond at the other. A proposed cis amide surrogate, the 1,5-disubstituted tetrazole, has been placed into a cyclic hexapeptide analog of somatostatin in order to constrain the putative cis amide bond. The final cyclization was done by either chemical or enzymatic means. The product, cyclo(Ala6-Tyr7-D-Trp8-Lys9-Val10-Phe11-psi[CN4] ), was found to have 83% of the activity of somatostatin. Solution nmr analysis in DMSO/water revealed that the backbone as well as side chain chi1 and chi2 were well ordered. Relaxation matrix methods were used to extract distance restraints from the nuclear Overhauser effect spectroscopy data set, and these were used in a systematic search of torsional space to identify structures consistent with the nmr data. Restrained minimizations of these structures using a number of different force fields produced structures having the expected beta II' turn at D-Trp8-Lys9 and a beta VIa turn in the Phe11-psi[CN4]-Ala6 portion of the molecule. The similarity of the minimized structures to those previously reported for cyclic hexapeptide analogues of somatostatin confirms the similarity of the tetrazole geometry to that of the cis amide in solution.

Three-dimensional solution structure of Cucurbita maxima trypsin inhibitor-V determined by NMR spectroscopy.

The solution structure of Cucurbita maxima trypsin inhibitor-V (CMTI-V), which is also a specific inhibitor of the blood coagulation protein, factor XIIa, was determined by 1H NMR spectroscopy in combination with a distance-geometry and simulated annealing algorithm. Sequence-specific resonance assignments were made for all the main-chain and most of the side-chain hydrogens. Stereospecific assignments were also made for some of the beta-, gamma-, delta-, and epsilon-hydrogens and valine methyl hydrogens. The ring conformations of all six prolines in the inhibitor were determined on the basis of 1H-1H vicinal coupling constant patterns; most of the proline ring hydrogens were stereospecifically assigned on the basis of vicinal coupling constant and intraresidue nuclear Overhauser effect (NOE) patterns. Distance constraints were determined on the basis of NOEs between pairs of hydrogens. Dihedral angle constraints were determined from estimates of scalar coupling constants and intraresidue NOEs. On the basis of 727 interproton distance and 111 torsion angle constraints, which included backbone phi angles and side-chain chi 1, chi 2, chi 3, and chi 4 angles, 22 structures were calculated by a distance geometry algorithm and refined by energy minimization and simulated annealing methods. Both main-chain and side-chain atoms are well-defined, except for a loop region, two terminal residues, and some side-chain atoms located on the molecular surface. The average root mean squared deviation in the position for equivalent atoms between the 22 individual structures and the mean structure obtained by averaging their coordinates is 0.58 +/- 0.06 A for the main-chain atoms and 1.01 +/- 0.07 A for all the non-hydrogen atoms of residues 3-40 and 49-67. These structures were compared to the X-ray crystallographic structure of another protein of the same inhibitor family-chymotrypsin inhibitor-2 from barley seeds [CI-2; McPhalen, C. A., & James, M. N. G. (1987) Biochemistry 26, 261-269]. The main-chain folding patterns are highly similar for the two proteins, which possess 62% sequence differences. However, major differences are noted in the N- and C-terminal segments, which may be due to the presence of a disulfide bridge in CMTI-V, but not in CI-2.

Preparation and characterization of a deoxyoligonucleotide 49-mer containing a site-specific thymidylyl-(3',5')-deoxyadenosine photoproduct.

Irradiation of d(GTATTATG) with 254 nm light gave rise to four major photoproducts, two of which were readily identified by NMR as the cis-syn cyclobutane dimer and the (6-4) photoproduct of the central TT site. Analysis of the NMR data for the other two photoproducts indicated that they were not any of the other known photoproducts of a TT site and might be TA* photoproducts [Bose, S. N., et al. (1983) Science 220, 723-725]. In support of this possibility, the fluorescence spectra of the products of acid hydrolysis of the two photoproducts were very similar to that reported for the hydrolysis product of the TA* photoproduct of TpdA. Only one of the two TA*-containing octamers could be ligated at both ends to form a 49-mer oligonucleotide in the presence of a complementary oligonucleotide scaffold, suggesting that the TA* photoproduct had formed between T5 and A6. The position of the TA* photoproduct was confirmed by mapping the arrest sites for 3'-->5' exonucleolytic degradation of the 49-mer by T4 DNA polymerase and for primer extension opposite the 49-mer by exonuclease deficient Klenow fragment (KF) and Sequenase Version 2.0. The TA* product could also be bypassed by both polymerases, but it was less of a block to KF. Treatment with 1 M aqueous piperidine at 100 degrees C led to a maximum of about 34% cleavage of the DNA at the site of the TA* product.(ABSTRACT TRUNCATED AT 250 WORDS)

Conformational analysis of two cyclic analogs of angiotensin: implications for the biologically active conformation.

Conformations of two cyclic analogs of angiotensin (Asp1-Arg2-Val3-Tyr4-Val/Ile5-His6-Pro7-Phe8, AT), cyclo[Sar1, Cys3, Mpt5]-AT and cyclo[Sar1, HCys3, Mpt5]-AT, were studied, independently employing two complementary techniques, energy calculations and NMR measurements in DMSO solution. NMR data were indicative of well-defined solution conformations for the cyclic moieties of cyclo[Sar1, Cys3, Mpt5]-AT and cyclo[Sar1, HCys3, Mpt5]-AT, including the phi values for the Cys3/HCys3 and Tyr4 residues, as well as the chi 1 value for the Tyr4 residue. Solution conformations for the exocyclic linear parts of both molecules cannot be described by the NMR data with the same precision. At the same time, independent energy calculations revealed the same conformations of cyclic moieties of cyclo[Sar1, Cys3, Mpt5]-AT and cyclo[Sar1, HCys3, Mpt5]-AT among low-energy conformers for both peptides. Moreover, the same conformations are compatible with the model of AT receptor-bound conformation (Nikiforovich & Marshall, 1993), which assumes the particular spatial arrangement of aromatic moieties of Tyr4, His6, and Phe8 residues and the C-terminal carboxyl. These conformers of cyclo[Sar1, Cys3, Mpt5]-AT and cyclo[Sar1, HCys3, Mpt5]-AT contain "an open turn" in the backbone of the Tyr4-Val5 residues, instead of the earlier proposed beta-like reversal, thus confirming the suggestion that the conformation(s) ensuring binding of AT analogs with specific receptors should not be described in terms of a unique backbone conformer.