Stishovite at the cretaceous-tertiary boundary, raton, new Mexico.

Stishovite, a dense phase of silica, has become widely accepted as an indicator of terrestrial impact events. Stishovite occurs at several impact structures but has not been found at volcanic sites. Solid-state silicon-29 magic-angle spinning nuclear magnetic resonance (silicon-29 MAS NMR) and X-ray diffraction of samples from the Cretaceous-Tertiary boundary layer at Raton, New Mexico, indicate that stishovite occurs in crystalline mineral grains. Stishovite was indicated by a single, sharp resonance with a chemical shift value of -191.3 ppm, characteristic of silicon in octahedral coordination, that disappeared after heating the sample at 850 degrees Celsius for 30 minutes. An X-ray diffraction pattern of HF residuals from the unheated sample displayed more than 120 peaks, most of which correspond to quartz, zircon, rutile, and anatase. Eight unambiguous weak to moderate reflections could be ascribed to d-spacings characteristic of stishovite.

The organic content of the Tagish Lake meteorite.

The Tagish Lake meteorite fell last year on a frozen lake in Canada and may provide the most pristine material of its kind. Analyses have now shown this carbonaceous chondrite to contain a suite of soluble organic compounds (approximately 100 parts per million) that includes mono- and dicarboxylic acids, dicarboximides, pyridine carboxylic acids, a sulfonic acid, and both aliphatic and aromatic hydrocarbons. The insoluble carbon exhibits exclusive aromatic character, deuterium enrichment, and fullerenes containing "planetary" helium and argon. The findings provide insight into an outcome of early solar chemical evolution that differs from any seen so far in meteorites.

13C-NMR spectroscopy of acetyltyrosyl-guanidinated horse heart cytochrome c.

The tyrosine residues of guanidinated horse heart cytochrome c have been specifically acetylated by reaction with N-[1-13C]acetylimidazole (90 atom%). Acetylation was monitored by 13C-NMR spectroscopy. The tyrosine residues were found to show widely varying reactivities ranging from one that is completely and exclusively acetylated at low reagent concentration (residue 67) to one that is acetylated only when the protein is unfolded (residue 97). Homogeneous derivatives were prepared containing one (either residue 67 or 97), three 48, 67 and 74), or four (residues 48, 67, 74 and 97) O-[1-13C]acetyl groups. 13C-NMR spectra of selected derivatives were obtained at pH 5.8, in the presence of cyanide ion, in the ferrous and ferric oxidation states, and after denaturation with 6M guanidine hydrochloride. The O-[1-13C]acetyltyrosyl resonances gave chemical shift values ranging from 171.8 to 176.0 ppm. These resonances were assigned to specific groups based on the known order of reactivity of the tyrosyl side chains toward N-acetylimidazole. The chemical shift of O-[1-13C]acetyltyrosyl 67 was found to be particularly sensitive to changes in protein structure. The proximity of this group to the heme makes it subject to distance-dependent paramagnetic and ring current effects. Acetylation of tyrosyl 74 gives rise to a pH-dependent equilibrium between conformers in the ferric state and a conformation change in the ferrous state. Acetylation of this residue also leads to an absorbance decrease at 695 nm that can be related to the 13C-NMR-detected conformational equilibrium. Addition of cyanide ion abolished this equilibrium.

Assignment of the aromatic 1H-NMR resonances of myotoxin a isolated from the venom of Crotalus viridis viridis.

The 400 MHz 1H-NMR spectrum of myotoxin a from the venom of Crotalus viridis viridis is described. The identification of spin systems in the aromatic region corresponding to the six aromatic residues of myotoxin a was completed using both one- and two-dimensional NMR spectroscopy and the pH dependence of chemical shifts. Assignments of these spin systems to specific residues was possible for the singly occurring amino acids Tyr-1 and Phe-12. Resonances from Tyr-1, His-5 and His-10 were shifted significantly from their random coil values in a pH-dependent manner. These shift perturbations were deemed evidence of a helical arrangement of the amino terminal region which placed these residues in close proximity to each other.

Ionization of tyrosine residues in horse-heart ferricytochrome c and its guanidinated and acetylated-guanidinated derivatives.

Spectrophotometric titration curves were obtained at 242 nm for native and fully guanidinated horse-heart ferricytochrome c. The cytochrome c data were fit over the pH range 9-12 (I = 0.35) by a theoretical curve with pK' values of 10.35 and 11.70. The slope of the experimental data increases sharply above pH 12.5 suggesting that two tyrosine residues with pK' values greater than 12.5 are exposed by conformation change. The guanidinated cytochrome c data after correction for the alkaline spin-state transition were fit over the entire pH range 9-13.6 (I = 0.35) by a theoretical curve with pK' values 10.37, 10.78, 11.50, and 13.60. These results along with viscosity measurements indicate that the unfolding transition occurs at higher pH in the guanidinated derivative. N-Acetylimidazole was used to acetylate specific tyrosyl groups of guanidinated cytochrome c. Assignments of acetylated tyrosine residues were confirmed by peptide mapping of 14C-labelled derivatives. Spectrophotometric titrations with rapid data acquisition of two monoacetylated derivatives allowed assignments of pK'1 (10.37) to Tyr-67 and pK'4 (13.60) to Tyr-97. The basis for the large differences in acidity and chemical reactivity of these two residues is not obvious from the crystallographic structure and may arise from differences in solvent access due to motions of the polypeptide chain.

The effect of cigarette smoking on the development of AIDS in HIV-1-seropositive individuals.

OBJECTIVE: To determine whether HIV-1-seropositive cigarette smokers progress more rapidly to AIDS than HIV-1-seropositive non-smokers. SETTING: The genitourinary medicine outpatient department of St Mary's Hospital, London, which is a London University teaching hospital (tertiary care centre). SUBJECTS AND DESIGN: Case series of 84 individuals with AIDS who provided accurate details of their smoking habits before their AIDS-defining diagnosis. MAIN OUTCOME MEASURE: Progression time to AIDS in relation to smoking habit. RESULTS: Progression time to AIDS (all diagnoses) was significantly reduced in HIV-1-seropositive smokers: median time to AIDS was 8.17 months for smokers (n = 43) and 14.50 months for non-smokers (n = 41) (P = 0.003). Smokers developed Pneumocystis carinii pneumonia (PCP) more rapidly than non-smokers, with a median time to PCP of 9.0 months, compared with 16.0 months for non-smokers (P = 0.002). Smoking had no significant effect on progression time to AIDS when not due to PCP. CONCLUSION: Cigarette smoking by HIV-1-seropositive individuals is associated with a more rapid development of AIDS and should be discouraged.

Effect of HIV-1 and cytomegalovirus in bronchoalveolar lavage cells on the transfer factor for lung carbon monoxide in AIDS patients.

Abnormalities in pulmonary function tests have been observed in AIDS patients with pulmonary disease. In this study, the polymerase chain reaction (PCR) was used to determine if the reductions in transfer factor for lung carbon monoxide (TLCO) were due to the presence of HIV-1 or cytomegalovirus (CMV). HIV-1 was detected in cells from bronchoalveolar lavage (BAL) in 35 out of 60 (58%) of patients. The detection of HIV-1 had no significant effect on pulmonary function. CMV was detected in the BAL of 58% of patients in this study but CMV was the sole viral pathogen in the lung of only two out of 60 (3.3%) individuals. A significant reduction in TLCO was observed in individuals with PCP where CMV was also detected in the BAL. This study shows that reduction in TLCO in HIV-seropositive patients is not due to the presence of HIV-1 or CMV alone in BAL cells.

Factors influencing participation in a rubella vaccination program.

During the course of a 7-day voluntary rubella vaccination program conducted at a large community-teaching hospital, 718 hospital workers were vaccinated, an overall vaccination rate of 29%. During and after the vaccination campaign, physicians, employees, and students were surveyed as to their reasons for accepting or rejecting rubella vaccine. Prior to the campaign few hospital workers realized that rubella vaccination was of importance in their case. Although paycheck notices, newsletters, and poster displays were all effective in publicizing the campaign, hospital workers most frequently cited discussions with other workers as the major factor leading to their acceptance of vaccination. The belief that a history of rubella, diagnosed clinically, was adequate assurance of immunity was common among physicians and employees and was the major obstacle to greater success in the campaign. Vaccine reactions were infrequent and mild and did not lead to excessive employee absenteeism.

Evidence for isomerization in myotoxin a from the prairie rattlesnake (Crotalus viridis viridis).

Myotoxin a, from the venom of the prairie rattlesnake, Crotalus viridis viridis, exists as a temperature-dependent equilibrium of two interconverting forms. Reverse-phase high-performance liquid chromatography (RP-HPLC) shows that the two forms interconvert slowly enough at 25 degrees C to be seen as two separate peaks with a molar ratio of c. 1:4. Each peak can be isolated and individually injected to give the same two peaks in the same ratio of areas. The two peaks merge during chromatography at elevated temperatures, indicating an increase in the rate of interconversion. At low temperature, c. 5 degrees C, the individual peaks can be isolated and maintained for several days without reaching equilibrium. Mass analysis by matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectrometry shows that myotoxin a is present in both RP-HPLC peaks, suggesting that the two resolved forms are conformational isomers. Capillary zone electrophoresis (CZE) also shows two resolved, but interconvertible peaks over a range of pH values. Furthermore, RP-HPLC chromatograms of myotoxin a at concentrations from 0.013 mM to 0.41 mM maintain a consistent ratio of peak areas, without evidence of dimerization. Two-dimensional 1H-NMR nuclear Overhauser enhancement spectroscopy indicates the presence of a cis-proline peptide bond, consistent with an equilibrium mixture of cis-trans isomers; however, addition of peptidyl-prolyl cis-trans isomerase (PPI) does not enhance the rate of equilibration of the RP-HPLC peaks isolated at c. 5 degrees C.

Photo-CIDNP detection of pyrimidine dimer radical cations in anthraquinonesulfonate-sensitized splitting.

Anthraquinone-2-sulfonate (AQS) photosensitizes pyrimidine dimer splitting. Electron abstraction from the dimer is thought to induce dimer splitting, but direct evidence for the existence and intermediacy of dimer radical cations has been lacking. By employing photochemically induced dynamic nuclear polarization, we have found emission signals in the NMR spectra of dimers upon photolysis of dimers in the presence of anthraquinone-2-sulfonate. The two dimers employed were cis, syn-thymine dimer in which the N(1)-positions were linked by a three-carbon bridge and the N(3), N(3')-dimethyl derivative of that compound. The anthraquinone-2-sulfonate sensitized photochemically induced dynamic nuclear polarization spectrum of the methylated derivative exhibited an emission signal from the dimer-C(6) hydrogens. This result implied the existence of a dimer radical cation (mD+.) formed by electron abstraction by excited anthraquinone-2-sulfonate and nuclear spin sorting within a solvent caged radical ion pair [mD+. AQS-.]. Product pyrimidine photochemically induced dynamic nuclear polarization signals were also seen [enhanced absorption by C(6)-hydrogens and emission by C(5)-methyl groups]. Nuclear spin polarization in the product resulted from spin sorting in one or more of its precursors, including mD+. The results support the conclusion that dimer radical cations not only exist but are intermediates in the photosensitized splitting of pyrimidine dimers by anthraquinonesulfonate.

Pneumothorax in patients with AIDS.

Eighty-seven inpatients were treated for 93 episodes of Pneumocystis carinii at St Mary's Hospital between January 1989 and December 1990. During this period, 298 patients with the acquired immunodeficiency syndrome (AIDS) were treated at this hospital. Sixteen episodes of pneumothorax occurred and 12 of these, occurring in ten patients, were unrelated to procedure. In six of 12 (50%), the pneumothoraces occurred concurrently with Pneumocystis carinii pneumonia (PCP) and in ten (83%) cases there was a past history of PCP. Bilateral pneumothorax occurred in five cases (42%). In seven (58%) of the cases, patients had been using aerosolized pentamidine as prophylaxis for PCP. This retrospective study confirms the association of pneumothorax with current PCP and also shows an association with previous infection. The use of aerosolized pentamidine was not associated with pneumothorax development. It is important to suspect pneumothorax in a patient with PCP who deteriorates acutely. The high incidence of bilateral pneumothorax means that pleurodesis should be considered early.

Growth and synthesis of nucleic Acid and protein by excised radish cotyledons.

Nutritional and light requirements for growth and synthesis of RNA, DNA, and protein by cotyledons excised from 5-day-old seedlings of Raphanus sativus L. were investigated, and the course of synthesis was followed through the cell cycle. The minimum requirements for a net increase in nucleic acid and protein were sugar, nitrate, and light. The cotyledons used nitrite at low concentration, but not ammonium ion. Light was required for preliminary steps in synthesis of RNA, DNA, and protein, but the actual polymerization reactions occurred in the dark. The cotyledons contained sufficient endogenous growth factors for about half of the cells to complete 1 cycle on a medium of 1% sucrose, 80 mm KNO(3). The increase in DNA was limited to about 50% and was accompanied by a comparable increase in cell number. Fresh weight, RNA, and protein tended to increase in proportion to DNA. Growth of the isolated cotyledons commenced with cell enlargement. RNA began to increase after about 4 hours, DNA after about 12. The major increase in protein also began at about 12 hours. The maximum rate of increase for all 3 occurred between 12 and 16 hours. Cell counts indicated that by 28 hours most of the cells which had replicated DNA had also completed cell division.

Interactive effects of salinity and phosphorus nutrition of the concentrations of phosphate and phosphate esters in mature photosynthesizing corn leaves.

The effects of salinity on corn plants (Zea mays L.) are influenced by the concentration of nutrient orthophosphate. Salinity (-2 bars each of NaCl and CaCl(2)) was more injurious in combination with a high concentration of orthophosphate (2 mm) (that gave optimum yields in the absence of salinity) than it was with a lower concentration (0.1 mm). With 2 mm orthophosphate, salinity seemed to damage the plant mechanisms that normally regulate the internal concentration of orthophosphate resulting in excessive accumulation and P toxicity. On the other hand, with 0.1 mm orthophosphate, salinity decreased orthophosphate concentration in mature leaves. This effect was paralleled by decreases in the concentration of adenosine 5'-triphosphate and in the energy charge of the adenylate system, indicating an orthophosphate deficit. Even so, plants survived salinity better under these conditions than in the presence of 2 mm orthophosphate. The data indicated that salinity affected the phosphorylated state of the adenine nucleotides only indirectly through its effect on the concentration of orthophosphate in the cells.Salinity, especially in the presence of 2 mm orthophosphate, resulted in an increase in the concentrations of sugar phosphates in mature photosynthesizing leaves, suggesting that translocation rather than photosynthesis was a limiting process. Decreased translocation could be a secondary effect of decreased growth. However, a decreased translocation rate could cause decreased growth by limiting the supply of essential metabolites reaching growing tissues.

Correlation between the Suppression of Glucose and Phosphate Uptake and the Release of Protein from Viable Carrot Root Cells Treated with Monovalent Cations.

Treating carrot (Daucus carota L.) discs with ice-cold NaCl solutions for 30 minutes caused three effects that appear to be functionally related: the exchange of tissue Ca(2+) and Mg(2+) for Na(+), the release of protein, and the suppression of active uptake of glucose and orthophosphate. Cyclosis continued apparently unabated after treatment with NaCl at concentrations of up to 0.25 m, so the cells remained viable and energetically competent. The correlation between the release of Ca(2+) and Mg(2+) and release of protein, and between these effects and the suppression of glucose and orthophosphate uptake, supports the hypothesis that divalent cations maintain, and monovalent cations disrupt, linkages between the outer cell surface and proteins required for active solute uptake. Calcium preserved uptake activity only when it was added in time to prevent the release of protein. Cells gradually recovered some glucose uptake activity after it had been completely inactivated by treatment with 0.25 m NaCl. This recovery occurred in the absence of added Ca(2+). It was inhibited by puromycin and so appears to require some protein synthesis. Beet (Beta vulgaris L.) discs were more resistant than carrot discs to treatment with NaCl solutions, thus reflecting the difference in tolerance of the two species to sodicity.

Intracellular pH of Cotton Embryos and Seed Coats during Fruit Development Determined by P Nuclear Magnetic Resonance Spectroscopy.

The pH of the phosphate-containing compartments of developing cotton seed coat and embryo tissues was determined by means of (31)P nuclear magnetic resonance spectroscopy. The pH values of these tissues varied as a function of developmental age. From 27 to approximately 38 days postanthesis, a strong pH differential existed between the two tissues; the seed coat was up to 1.4 pH units more acid than developing cotton embryos. The pattern of pH values found with this technique agrees with pH values of tissue homogenates in distilled water. The results confirm an earlier suggestion that seed coat cells are more acidic than embryo cells during key developmental stages of the seed. The pH differential between these two tissues causes abscisic acid to diffuse from seed coats to embryos against its apparent concentration gradient to prevent viviparous germination, despite a higher abscisic acid concentration in the embryo.

Nucleotide Metabolism in Salt-Stressed Zea mays L. Root Tips: I. Adenine and Uridine Nucleotides.

Corn plants (Zea mays L. cv Pioneer 3906) were grown in a glass house on control and saline nutrient solutions, in winter and summer. There were two saline treatments, both with osmotic potential = -0.4 megapascal but with different Ca(2+)/Na(+) ratios: 0.03 and 0.73. Root tips and shoot meristems (culm tissue) of 26 day-old plants were analyzed for nucleotides to ascertain if there were correlations between nucleotide pool size and the reduced growth on saline cultures. Several other cell components also were determined. Plants grown in winter were only half as large as those grown in summer mainly because of the lower light intensity and lower temperature. But the relative yield reduction on salt treatment compared to the control was similar in winter and summer. The two different salt treatments caused similar yield reductions. Neither salt treatment affected nucleotide pools in culm tissue, with the possible exception of UDPG in winter. In the case of root tips, salt treatment had little or no effect on nucleotide pool sizes in winter when many already seemed near a critical minimum, but in summer it reduced several pools including ATP, total adenine nucleotide, UTP, total uridine nucleotide, and UDP-glucose. The reductions were greatest on the salt treatment with low Ca(2+)/Na(+). There was no simple correlation between the effects of salt stress on growth and on nucleotide pool size. The nucleotide pools of culm tissue indicated that in some respects this tissue was effectively insulated from the salt stress. Roots that were in direct contact with the saline solution indicated significant reductions in nucleotide pools only in the summer whereas growth was reduced both summer and winter. It is possible that the nucleotide concentrations of root cells in winter were already near a critical minimum so that nucleotide synthesis and growth were tightly linked. Significant reductions in nucleotide pools that would be expected to affect growth were more evident in summer when pools were larger and growth was more rapid. But even where ATP and total adenine nucleotides were reduced, the ratio of ATP:ADP and the adenylate energy charge remained unchanged indicating an active adenylate kinase that had access to most of the adenine nucleotide pools, and possible catabolism of excess AMP.

Assignment of fluorine nuclear magnetic resonance signals from rabbit cyanomethemoglobin.

A fluorine NMR study of cyanomethemoglobin prepared from hemoglobin isolated from rabbits maintained on a diet containing DL-p-fluorophenylalanine is described. The results indicate that substitution of fluorophenylalanine occurs essentially randomly at all phenylalanine positions of the alpha- and beta-globin chains; a set of hybrid hemoglobins in which only the alpha- or only the beta-chains contain the fluorinated amino acid was prepared and used to ascertain the fluorine NMR signals arising from each chain. The temperature and pH dependences of chemical shifts, spin-lattice relaxation times, 19F(1H) nuclear Overhauser effects, and the effect of chemical modification of the beta-93 sulfhydryl groups were examined. When considered in light of presently available X-ray structures of human and horse hemoglobins, the available data permit a tentative assignment of most signals to particular fluorophenylalanine/phenylalanine positions in the globin sequences.