Routine 24-Hour Computed Tomography Brain Scan is not useful in stable patients Post Intravenous Tissue Plasminogen Activator.

BACKGROUND: Obtaining a routine computed tomography (CT) brain scan 24 hours after treatment with intravenous tissue plasminogen activator (IV-tPA) is included in the American Heart Association/American Stroke Association acute stroke guidelines. The usefulness of the test in stable patients is not known. We hypothesized that the results of routine, 24-hour post-treatment neuroimaging (CT or magnetic resonance imaging [MRI] brain scans) would not alter the management of clinically stable patients. METHODS: Patients treated with IV-tPA between January 2011 and December 2013 were identified from a single hospital's stroke registry. All patients were closely monitored for changes in stroke severity. Demographics, changes in neurological status, neuroimaging results, and changes in therapy were abstracted from the patients' medical records. Patients having a neuroimaging study because of neurological deterioration were excluded. RESULTS: Of 136 patients treated with IV-tPA, 131 met criteria for inclusion. Of these, 86.7% had moderate to severe neurological deficits (i.e., initial National Institutes of Health Stroke Scale score > 5 points; median 8 points). All patients had routine imaging ~24 hours after treatment (CT brain 62.6%, MRI brain 12.4%, both CT and MRI brain 25%). Asymptomatic hemorrhagic transformation occurred in 6.7% and potentially changed management in a single patient (target systolic blood pressure was lowered from 185 to 180 mmHg). CONCLUSIONS: Over a 3-year period, routine neuroimaging ~24-hours after IV-tPA in clinically stable patients was associated with a change in therapy in only 1 (.95%) patient. If confirmed in other cohorts, these results suggest that routine neuroimaging after IV-tPA may be safely avoided in clinically stable patients, eliminating unnecessary radiation exposure in those having CT brain and reducing costs.

The IMAGINE instrument: first neutron protein structure and new capabilities for neutron macromolecular crystallography.

The first high-resolution neutron protein structure of perdeuterated rubredoxin from Pyrococcus furiosus (PfRd) determined using the new IMAGINE macromolecular neutron crystallography instrument at the Oak Ridge National Laboratory is reported. Neutron diffraction data extending to 1.65 Šresolution were collected from a relatively small 0.7 mm(3) PfRd crystal using 2.5 d (60 h) of beam time. The refined structure contains 371 out of 391, or 95%, of the D atoms of the protein and 58 solvent molecules. The IMAGINE instrument is designed to provide neutron data at or near atomic resolution (1.5 Å) from crystals with volume <1.0 mm(3) and with unit-cell edges <100 Å. Beamline features include novel elliptical focusing mirrors that deliver neutrons into a 2.0 × 3.2 mm focal spot at the sample position with full-width vertical and horizontal divergences of 0.5 and 0.6°, respectively. Variable short- and long-wavelength cutoff optics provide automated exchange between multiple-wavelength configurations (λmin = 2.0, 2.8, 3.3 Što λmax = 3.0, 4.0, 4.5, ∼20 Å). These optics produce a more than 20-fold increase in the flux density at the sample and should help to enable more routine collection of high-resolution data from submillimetre-cubed crystals. Notably, the crystal used to collect these PfRd data was 5-10 times smaller than those previously reported.

Exploring the Relationship Between Objective Pupillometry Metrics and Midline Shift.

ABSTRACT: BACKGROUND: Pupillary examinations provide early subtle signs of worsening intracranial pathology. Objective pupillomtery assessment, although not yet the standard of care, is considered best practice. However, inconsistent findings from objective pupillometry studies have caused a lack of consensus among clinicians; as such, no clinical guidelines are available to guide clinical use of objective pupillometer devices. To add to the body of evidence, the purpose of this project was to explore the relationship between objective pupillometry metrics and midline shift (MLS). METHODS: A retrospective chart review of pupillometer data was conducted. Midline shift was correlated with objective pupillometry metrics including Neurological Pupil Index (NPi), pupil size, and anisocoria. Midline shift was measured for the patient's initial neuroimaging and with any defined neurological change. Spearman ρ was used for statistical analysis of correlations between pupillometer metrics and MLS measured at both the septum pellucidum and pineal gland. RESULTS: A total of 41 patients were included in the analysis; most were White (58.5%) and male (58.5%), with a mean (SD) age of 58.49 (16.92) years. Spearman ρ revealed statistically significant positive correlations between right pupil NPi and anisocoria with MLS, and significant negative correlations between left pupil NPi and pupil size with MLS. CONCLUSIONS: Results from this project are consistent with previous studies. Objective pupillometry continues to be a valuable component of a comprehensive neurological examination, because it has the ability to discern early and subtle changes in a patient's neurological status, leading to lifesaving interventions.

S100B and brain natriuretic peptide predict functional neurological outcome after intracerebral haemorrhage.

OBJECTIVE: To determine the predictive value of S100b and brain natriuretic peptide (BNP) in order to determine accurately and quickly a discharge prognosis after primary supratentorial intracerebral haemorrhage (ICH). METHODS: After IRB approval and informed consent, blood samples were obtained and analysed from 28 adult patients consecutively admitted to the neuroscience intensive care unit with computed tomography-proven supratentorial ICH from June 2003 and December 2004 within the first 24 h after symptom onset for S100b and BNP. Functional outcomes on discharge were dichotomized to favourable (mRS < 3) or unfavourable. RESULTS: BNP (a neurohormone) and S100b (a marker of glial activation) were found to be independently highly predictive of functional neurological outcome at the time of discharge as measured by the modified Rankin Score (BNP: p < 0.01, r = 0.46; S100b: p < 0.01, r = 0.42) and the Barthel Index (BNP: p < 0.01, r = 0.54; s100b: p < 0.01, r = 0.50). Although inclusion of either biomarker produced additive value when included with traditional clinical prognostic variables, such as the ICH score (Barthel index: p < 0.01, r = 0.66; mRS: p < 0.01, r = 0.96), little predictive power is added with inclusion of both biomarkers in a regression model for neurological outcome. CONCLUSIONS: Serum S100b and BNP levels in the first 24 h after injury accurately predict neurological function at discharge after supratentorial ICH.

Apolipoprotein E modifies neurological outcome by affecting cerebral edema but not hematoma size after intracerebral hemorrhage in humans.

INTRODUCTION: To address the mechanisms by which apoE polymorphism affects functional outcome after intracerebral hemorrhage in humans, we tested the hypothesis that the presence of the APOE4 allele results in amplified inflammatory responses and increased cerebral edema. METHODS: We prospectively enrolled and collected data on 21 adult patients consecutively admitted to Duke University Hospital with supratentorial intracerebral hematoma including hemorrhage volume, midline shift, modified Rankin Score, Glasgow Outcome Score, and APOE genotype. Hemorrhage size (cm(3)) and midline shift (mm), at the level of the thalamus, were measured by computed tomography within 36 hours of admission. Rankin and Glasgow Scores were determined at discharge. Student's t-test was used to analyze hemorrhage size, midline shift, and Glasgow Outcome Score and logistical regression were used to measure allele affect on modified Rankin Score. When analyzing modified Rankin Score, patients were grouped by favorable outcome (0-2) or unfavorable (3-6). RESULTS: Out of 21 patients, 11 possessed at least 1 APOE4 allele (APOE4+). There was no difference in hemorrhage volume (25.8 v 38.3 mm for APOE4- v APOE4+, respectively) between the groups, but there was a significant difference in midline shift (P = .04, 0.7 v 4 mm). Functional outcomes were worse for the patients possessing at least 1 APOE4 allele (P = .04) CONCLUSION: The presence of APOE4 is associated with poor functional outcomes in humans after intracerebral hemorrhage. Our data suggest that the mechanism for this may be increased cerebral edema and not larger hematoma volume.

Risk of cerebral vasopasm after subarachnoid hemorrhage reduced by statin therapy: A multivariate analysis of an institutional experience.

OBJECT: Impairment of endothelial nitric oxide synthase (eNOS), endothelium-dependent relaxation, and cerebrovascular autoregulation all occur in vasospastic cerebral arteries following subarachnoid hemorrhage (SAH). The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, both improve endothelial function and increase eNOS messenger RNA, protein, and enzymatic activity threefold. Increasing experimental evidence in animal models of SAH suggests that statins may ameliorate cerebral vasospasm. The authors hypothesized that patients chronically treated with statins would have a decreased risk of symptomatic vasospasm after SAH. METHODS: The authors retrospectively reviewed the charts of 115 patients with SAH who were consecutively admitted to the Neuroscience Intensive Care Unit of Duke University between 1998 and 2001. The independent association of statin therapy to symptomatic vasospasm was assessed using multivariate logistic regression analysis. Fifteen patients (13%) admitted with SAH were receiving statin therapy for at least 1 month before admission. Forty-nine patients (43%) experienced symptomatic vasospasm a mean of 5.8 +/- 3 days after onset of SAH. Current statin therapy on admission (odds ratio [OR] 0.09, 95% confidence interval [CI] 0.01-0.77) was independently associated with an 11-fold reduction in the risk of symptomatic vasospasm. Fisher Grade 3 SAH (OR 2.82, 95% CI 1.50-5.71) and rupture of anterior cerebral or internal carotid artery aneurysm (OR 3.77, 95% CI 1.29-10.91) were independently associated with an increased risk of symptomatic vasospasm. CONCLUSIONS: In this retrospective case series, patients who received statin therapy for at least 1 month demonstrated an 11-fold decrease in the risk of developing symptomatic vasospasm after SAH.

The Duke neurology advanced practice provider residency: Its time has come.

The acknowledgment that specialization in neurology based on a clinician's extensive background in neuroscience contributes to expertise in patient care was a motivating factor in developing neurology residency programs. The increasing demand for more and better access to neurologic care has created a health care environment ripe for innovation. Advanced practice providers currently do not have the opportunity during primary training to gain much experience in neurologic care. We discuss the challenges and benefits of developing a 1-year neurology residency program for nurse practitioner and physician assistant graduates at our institution. We propose that providing advanced practice providers with specialty skills through neurology residency programs such as ours will be integral to meet the growing clinical need for neurologic care.

Simvastatin reduces vasospasm after aneurysmal subarachnoid hemorrhage: results of a pilot randomized clinical trial.

BACKGROUND AND PURPOSE: Cerebral vasospasm remains a major source of morbidity after aneurysmal subarachnoid hemorrhage (SAH). We demonstrate that simvastatin reduces serum markers of brain injury and attenuates vasospasm after SAH. METHODS: Patients with angiographically documented aneurysmal SAH were randomized within 48 hours of symptom onset to receive either simvastatin (80 mg daily; n=19) or placebo (n=20) for 14 days. Plasma alanine aminotransferase, aspartate aminotransferase, and creatine phosphokinase were recorded weekly to evaluate laboratory evidence of hepatitis or myositis. Serum markers of brain injury were recorded daily. The primary end point of vasospasm was defined as clinical impression (delayed ischemic deficit not associated with rebleed, infection, or hydrocephalus) in the presence of > or =1 confirmatory radiographic test (angiography or transcranial Doppler demonstrating mean V(MCA) >160 m/sec). RESULTS: There were no significant differences in laboratory-defined transaminitis or myositis between groups. No patients developed clinical symptoms of myopathy or hepatitis. Plasma von Willebrand factor and S100beta were decreased 3 to 10 days after SAH (P<0.05) in patients receiving simvastatin versus placebo. Highest mean middle cerebral artery transcranial Doppler velocities were significantly lower in the simvastatin-treated group (103+/-41 versus 149+/-47; P<0.01). In addition, vasospasm was significantly reduced (P<0.05) in the simvastatin-treated group (5 of 19) compared with those who received placebo (12 of 20). CONCLUSIONS: The use of simvastatin as prophylaxis against delayed cerebral ischemia after aneurysmal SAH is a safe and well-tolerated intervention. Its use attenuates serum markers associated with brain injury and decreases the incidence of radiographic vasospasm and delayed ischemic deficit.

Novel diagnostic test for acute stroke.

BACKGROUND AND PURPOSE: The absence of a widely available and sensitive diagnostic test for acute cerebral ischemia remains a significant limitation in the diagnosis and management of stroke. The objective of this study was to examine the feasibility of developing a diagnostic panel of blood-borne biochemical markers of cerebral ischemia. METHODS: Serial blood samples were obtained from patients (n=65 with suspected ischemic stroke, n=157 control subjects) presenting to an academic medical center emergency department. We analyzed 26 blood-borne markers believed to play a role in the ischemic cascade and created a 3-variable logistic regression model to predict the clinical diagnosis of stroke, defined as persistent neurological symptoms of cerebral ischemia lasting >24 hours. RESULTS: Of the 26 blood-borne markers analyzed, univariate logistic analysis revealed that 4 were highly correlated with stroke (P<0.001): a marker of glial activation (S100beta), 2 markers of inflammation (matrix metalloproteinase-9 and vascular cell adhesion molecule), and 1 marker of thrombosis (von Willebrand factor). When the outcome level was set to a cutoff of P=0.1, our logistic model provided a sensitivity and specificity of 90% for predicting stroke. CONCLUSIONS: A panel of blood-borne biochemical markers may be helpful in identifying patients with acute cerebral ischemia who could benefit from urgent care. Such a test may also be helpful in identifying stroke patients in the prehospital setting so that they could be fast-tracked to an institution equipped to care for patients with acute stroke.

Correlation of serum brain natriuretic peptide with hyponatremia and delayed ischemic neurological deficits after subarachnoid hemorrhage.

OBJECTIVE: Serum brain natriuretic peptide (BNP) is elevated after subarachnoid hemorrhage (SAH), causes diuresis and natriuresis (cerebral salt wasting), and may exacerbate delayed ischemic neurological deficits. We examined the temporal relationship between serum BNP elevation, hyponatremia, and the onset of delayed ischemic neurological deficits and determined whether serum BNP levels correlated with the 2-week outcome after SAH. METHODS: Serum BNP and sodium were measured prospectively every 12 hours for 14 days in 40 consecutive patients admitted with SAH. All patients remained euvolemic, underwent transcranial Doppler assessment every 48 hours, and underwent angiography at the onset of delayed neurological deficits. New-onset neurological deficits were attributed to vasospasm only in the absence of other causes and when supported by transcranial Doppler or cerebral angiography. RESULTS: Sixteen patients (40%) experienced symptomatic cerebral vasospasm after SAH. A more than threefold increase in admission serum BNP was associated with the onset of hyponatremia (P < 0.05). Mean BNP levels were similar between vasospasm and nonvasospasm patients fewer than 3 days after SAH (126 +/- 39 pg/ml versus 154 +/- 40 pg/ml; P = 0.61) but were elevated in the vasospasm cohort 4 to 6 days after SAH (285 +/- 67 pg/ml versus 116 +/- 30 pg/ml; P < 0.01), 7 to 9 days after SAH (278 +/- 72 pg/ml versus 166 +/- 45 pg/ml; P < 0.01), and 9 to 12 days after SAH (297 +/- 83 pg/ml versus 106 +/- 30 pg/ml; P < 0.01). BNP level remained independently associated with vasospasm adjusting for Fisher grade and Hunt and Hess grade (odds ratio, 1.28; 95% confidence interval, 1.1-1.6). In patients in whom vasospasm developed, mean serum BNP increased 5.4-fold within 24 hours after vasospasm onset and 11.2-fold the first 3 days after vasospasm onset. Patients with increasing BNP levels from admission demonstrated no change (0 +/- 3) in Glasgow Coma Scale score 2 weeks after SAH versus a 3.0 +/- 2 (P < 0.05) improvement in Glasgow Coma Scale score in patients without increasing serum BNP levels. CONCLUSION: Increasing serum BNP levels independently were associated with hyponatremia, significantly increased the first 24 hours after onset of delayed ischemic neurological deficits, and predicted the 2-week Glasgow Coma Scale score.

Serum von Willebrand factor, matrix metalloproteinase-9, and vascular endothelial growth factor levels predict the onset of cerebral vasospasm after aneurysmal subarachnoid hemorrhage.

OBJECTIVE: Endothelial damage and intimal proliferation occur in vasospastic cerebral arteries after subarachnoid hemorrhage (SAH). In the peripheral vasculature, endothelial damage increases intimal matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor (VEGF) levels, causing neointimal proliferation. We hypothesized that serum von Willebrand factor (vWF) (a marker of endothelial cell death), MMP-9, and VEGF levels could serve as prognostic markers in predicting the occurrence of cerebral vasospasm. METHODS: Venous serum vWF, MMP-9, and VEGF levels were prospectively measured daily, for 12 days or until the onset of vasospasm, for 45 consecutive patients admitted with SAH (n = 38) or admitted for elective aneurysm clipping (control subjects, n = 7). The development of transcranial Doppler flow velocities of more than 180 cm/s and/or new focal neurological deficits with angiographically confirmed vasospasm was considered the onset of vasospasm. To establish whether these markers were specific for vasospasm versus ischemia, blood samples were obtained from a concurrent group of 42 patients within 24 hours after stroke onset unrelated to SAH. RESULTS: Fifty-seven percent of patients (22 of 38 patients) developed vasospasm, 4 to 11 days after SAH (median, 7 d). Mean peak serum vWF, MMP-9, and VEGF levels were increased in the SAH prevasospasm cohort, compared with the SAH nonvasospasm cohort (vWF, 5526 +/- 929 versus 4934 +/- 599 ng/ml, P = 0.01; MMP-9, 705 +/- 338 versus 438 +/- 154 ng/ml, P = 0.006; VEGF, 0.12 +/- 0.06 versus 0.06 +/- 0.06 ng/ml, P = 0.023). Mean peak vWF, MMP-9, and VEGF levels for the focal ischemia cohort (vWF, 4645 +/- 875 ng/ml, P = 0.01; MMP-9, 250 +/- 308 ng/ml, P = 0.001; VEGF, 0.03 +/- 0.04 ng/ml, P = 0.001) were markedly lower in comparison with the SAH prevasospasm cohort and were unchanged in comparison with the control cohort. vWF levels of more than 5500 ng/ml, VEGF levels of more than 0.12 ng/ml, and MMP levels of more than 700 ng/ml each independently increased the odds of subsequent vasospasm (18-, 20-, and 25-fold, respectively). CONCLUSION: The development of cerebral vasospasm after SAH was preceded by increases in serum vWF, MMP-9, and VEGF levels. Increased serum vWF, MMP-9, and VEGF levels could accurately predict the onset of cerebral vasospasm after SAH. These factors were not elevated by SAH alone or in a separate cohort of patients with ischemic stroke, suggesting that these factors might play a role in the pathogenesis of human cerebral vasospasm.

Algebraic direct methods for few-atoms structure models.

As a basis for direct-methods phasing at very low resolution for macromolecular crystal structures, normalized structure-factor algebra is presented for few-atoms structure models with N = 1, 2, 3, em leader equal atoms or polyatomic globs per unit cell. Main results include: [see text]. Triplet discriminant Delta(hk) and triplet weight W(hk) parameters, a approximately 4.0 and b approximately 3.0, respectively, were determined empirically in numerical error analyses. Tests with phases calculated for few-atoms 'super-glob' models of the protein apo-D-glyceraldehyde-3-phosphate dehydrogenase (approximately 10000 non-H atoms) showed that low-resolution phases from the new few-atoms tangent formula were much better than conventional tangent formula phases for N = 2 and 3; phases from the two formulae were essentially the same for N > or = 4.

Transcranial Doppler monitoring and clinical decision-making after subarachnoid hemorrhage.

Our objective was to examine the impact of transcranial Doppler ultrasound (TCD) vasospasm monitoring on clinical decision-making following subarachnoid hemorrhage (SAH). The records of 50 randomly selected patients undergoing serial TCD monitoring following SAH were reviewed. Dates and results of TCDs and cerebral angiograms, the use of hypertensive hemodilution (HH) therapy, and the development of new neurological deficits were recorded. The independent effects of TCD-defined vasospasm and new neurological deficits on patient management were determined with multiple logistical regression. Results were validated in a second randomly selected, 50 patient cohort. Mild or moderate TCD-defined vasospasm developed in 76% of patients 5.8 +/- 0.5 days after SAH; 38% developed severe TCD-defined vasospasm after 7.9 +/- 0.7 days. Focal neurological deficits occurred in 50% after 5.7 +/- 0.6 days with TCD abnormalities preceding the deficit by 2.5 +/- 0.7 days in 64%. TCD-defined vasospasm or a new neurological deficit explained 60% of the variance in the use of HH therapy (P = .005). New neurological deficits increased the odds of HH therapy 33-fold (P = .004) whereas there was no independent effect of TCD-defined vasospasm. These variables explained 64% of the variance in the performance of angiography (P = .0002). An abnormal TCD did not increase the odds of angiography whereas its use increased 28-fold (P = .01) after a neurological deficit developed. These results were confirmed in an independent cohort. We concluded that TCD-defined vasospasm did not independently influence the use of HH therapy or angiography with both decisions associated with the development of new neurological deficits. As TCD-defined vasospasm preceded the neurological deficit in 64%, earlier intervention might reduce the incidence of vasospasm-related stroke in institutions with similar practice patterns.

The structure of T6 bovine insulin.

Porcine insulin differs in sequence from bovine insulin at residues A8 (Thr in porcine-->Ala in bovine) and A10 (Ile in porcine-->Val in bovine). The structure of T6 hexameric bovine insulin has been determined to 2.25 A resolution at room temperature and refined to a residual of 0.162. The structure of the independent dimer is nearly identical to the T6 porcine insulin dimer: the mean displacement of all backbone atoms is 0.16 A, with the largest displacements occurring at AlaB30. Each of two independent zinc ions is octahedrally coordinated by three HisB10 side chains and three water molecules. As has been observed in both human and porcine insulin, the GluB13 side chains are directed towards the center of the hexamer, where a short contact of 2.57 A occurs between two independent carboxyl O atoms, again suggesting the presence of a centered hydrogen bond. No significant displacements of backbone atoms or changes in conformation are observed at A8 or A10. Since there are no interhexamer hydrogen-bonded contacts involving A8 in either porcine or bovine insulin, the change in the identity of this residue appears to have little or no effect upon the packing of the hexamers in the unit cell. In contrast, the side chains of the three A10 residues in one trimer make van der Waals contacts with the A10 side chains in a translationally related hexamer. As a consequence of the loss of the C(delta1) atom from the isoleucine residue in porcine insulin to produce valine in bovine insulin, there is a 0.36 A decrease in the distance between independent pairs of C(beta) atoms and a 0.24 A decrease in the c dimension of the unit cell. Thus, the net effect of the change in sequence at A10 is to strengthen the stabilizing hydrophobic interactions between hexamers.

Lessons from an aged, dried crystal of T(6) human insulin.

The structure of the T(6) hexameric form of human insulin has been determined at both room temperature and 100 K from a single air-dried crystal. At 100 K, the space group is R3 and the asymmetric unit consists of a dimer, as has been observed previously in hydrated structures. At room temperature, the space group is P1 and the unit cell contains a quasi-threefold-symmetric hexamer. In the absence of stabilizing water interactions, the N-termini of all six A chains in the room-temperature structure appear to have undergone partial unfolding, but the N-termini of these chains are well ordered in the 100 K structure. Other differences between the room-temperature and 100 K structures involve the coordination around the zinc ions. At 100 K, both zinc ions clearly exhibit dual coordination: zinc is octahedrally coordinated in one half of the zinc sites but tetrahedrally coordinated in the other half; at room temperature, the electron densities suggest tetrahedral coordination but the bond distances to the fourth ligands are longer than expected. Contrary to what has been observed to date in all other T(6) insulin structures, there are no contacts between pairs of GluB13 residues, either at room temperature or at 100 K, that would suggest the presence of a hydrogen bond. At room temperature, three of the six independent GluB13 side chains are disordered; at 100 K, both independent side chains are disordered. The disorder in the GluB13 side chains and the lack of contacts between carboxylate groups suggests that as a result of disruption of the hydration structure in the central core of the hexamer, all six B13 carboxylates bear a negative charge. This in turn suggests that in the hydrated structures the well ordered water structure in the central core is involved in stabilizing the B13 side-chain conformations and modulating charge repulsions among the six B13 glutamates if they are not protonated, or that, as is considered more likely, the water structure plays an important role in modulating the pK(a) values of the B13 glutamates, resulting in protonation and hydrogen-bond formation.

The structure of T6 human insulin at 1.0 A resolution.

The structure of T(6) human insulin has been determined at 120 K at a resolution of 1.0 A and refined to a residual of 0.183. As a result of cryofreezing, the first four residues of the B chain in one of the two crystallographically independent AB monomers in the hexameric [Zn(1/3)(AB)(2)Zn(1/3)](3) complex undergo a conformational shift that displaces the C(alpha) atom of PheB1 by 7.86 A relative to the room-temperature structure. A least-squares superposition of all backbone atoms of the room-temperature and low-temperature structures yielded a mean displacement of 0.422 A. Omitting the first four residues of the B chain reduced the mean displacement to 0.272 A. At 120 K, nine residues were found to exhibit two discrete side-chain conformations, but only two of these residues are in common with the seven residues found to have disordered side chains in the room-temperature structure. As a result of freezing, the disorder observed at room temperature in both ArgB22 side chains is eliminated. The close contact between pairs of O( epsilon 2) atoms in GluB13 observed at room temperature is maintained at cryotemperature and suggests that a carboxylate-carboxylic acid centered hydrogen bond exists [-C(=O)-O.H.O-C(=O)-] such that the H atom is equally shared between the two partially charged O atoms.