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Biomedical subjects

S M Green

Publications and source records attributed to S M Green.

At least 19 recordsLinked to original sources
PubMed1992

Contributions of the polar, uncharged amino acids to the stability of staphylococcal nuclease: evidence for mutational effects on the free energy of the denatured state.

In order to quantitate the contributions of the polar, uncharged amino acids to the stability of the native state of staphylococcal nuclease, each of the 13 alanines, 9 glycines, 9 threonines, 6 prolines, 6 glutamines, 6 asparagines, and 3 serines was substituted, either with both alanine and glycine or with 1 of these 2 amino acids plus valine. For each mutant, the stability to reversible denaturation (delta GH2O) was quantitated by determining the Kapp for this reaction as a function of guanidine hydrochloride concentration. In addition, the parameter mGuHCl (= d(delta G)/d[GuHCl]) was calculated from the data. To identify the local structural features responsible for the relatively large and variable changes in delta GH2O and mGuHCl observed for the same type of substitution at different locations in nuclease, statistical correlations were sought between delta GH2O, mGuHCl, and a number of descriptors of the local structure. As with substitutions of the large hydrophobic amino acids [Shortle, D., Stites, W. E., & Meeker, A. K. (1990) Biochemistry 29, 8033-8041], mutation of polar, uncharged residues to Gly leads to a change in stability that, on average, correlates well with the degree to which the wild-type residue is buried. This correlation is especially significant for threonine, an amino acid with both polar and hydrophobic character, but is not demonstrated for the more typically hydrophobic residue alanine. As reported in the previous study of alanine/glycine substitutions of hydrophobic residues, a significant correlation between changes in stability and changes in the value of mGuHCl is again observed, strengthening the conclusion that the putative structural changes in the denatured state which lead to increases or decreases in mGuHCl are responsible for a significant fraction of the stability loss for an average mutant. The existence of this correlation is consistent with the denatured state of wild-type staphylococcal nuclease having evolved to a relatively high free energy via optimization of a balance between a maximal exposure of hydrophobic surface and a minimal gain in chain entropy. On average, mutations are less stable in proportion to the extent of which they perturb this balance. A new and puzzling correlation is reported between the extent of buriedness of a residue in the wild-type native state versus the difference in mGuHCl between the Ala mutation and the Gly mutation at that position.

Alanine↗
PubMed1992

The effects of scaphoid intercarpal stabilizations on wrist mechanics: an experimental study.

A fresh cadaver study of the effects of a variety of scaphoid stabilizations on wrist motions is reported. Scaphoid-trapezium-trapezoid stabilizations with the scaphoid in its normal anatomic position and the same stabilizations with the scaphoid in malposition, either vertical or horizontal in relation to the radius, were compared. Scaphoid-capitate stabilizations with the scaphoid in its normal position were also studied. With the scaphoid vertical, a scaphoid-trapezium-trapezoid stabilization resulted in greater loss of wrist flexion and ulnar deviation whereas, with the scaphoid horizontal, wrist extension and radial deviation were more severely affected than when the scaphoid was stabilized in its normal position. With the scaphoid in its anatomic position, both scaphoid-trapezium-trapezoid and scaphoid-capitate stabilizations resulted in similar patterns of wrist motion.

Bone Nails↗
PubMed1992

Plain abdominal radiography in the detection of major disease in children: a prospective analysis.

STUDY OBJECTIVE: To prospectively evaluate previously described high-yield clinical criteria for obtaining plain abdominal radiographs in the emergency evaluation of children. DESIGN: Prospective, observational study. SETTING: Emergency departments of a university medical center and an affiliated county hospital. PARTICIPANTS: Three hundred fifty-four children 15 years old or younger who underwent plain abdominal radiography during a one-year period. METHODS AND MEASUREMENTS: Physicians ordering plain abdominal radiographs completed data forms that included historical and physical examination information before viewing films. At a later date, records of all patients were reviewed for radiologist interpretation and final diagnosis. The data were analyzed to determine the sensitivity, specificity, and predictive values of previously described high-yield criteria (from a retrospective series) in detecting radiographs that were diagnostic or suggestive of "major" abdominal disease. MAIN RESULTS: Sixty-one patients (17%) had major diseases potentially requiring procedural intervention (eg, appendicitis, ingested foreign bodies, and intussusception), whereas 296 patients (83%) had minor diseases not requiring procedural intervention (eg, gastroenteritis and nonabdominal diagnoses). The presence of any of the following features--prior abdominal surgery, foreign body ingestion, abnormal bowel sounds, abdominal distention, or peritoneal signs--was 93% sensitive and 40% specific in detecting diagnostic or suggestive radiographs in patients with major disease. Positive and negative predictive values were 11% and 99%, respectively. If only these criteria had been used to obtain radiographs, 38% of films would have been omitted (at an estimated savings of $20,000) with only two suggestive radiographs missed. CONCLUSION: Our results suggest that restricting abdominal radiographs to patients with at least one of these five high-yield clinical features will detect most diagnostic and suggestive radiographs in children with major abdominal diseases.

Abdomen↗
PubMed1992

Pediatric bacterial meningitis: is prior antibiotic therapy associated with an altered clinical presentation?

STUDY HYPOTHESIS: The clinical features of children treated with oral antibiotics before the diagnosis of bacterial meningitis differ from those who receive no antibiotics. DESIGN: Retrospective case series. SETTING: University medical center. PARTICIPANTS: Two hundred fifty-eight children 24 months old or younger with bacterial meningitis hospitalized during a 12-year period. Eighty-three children were treated with oral antibiotics before the diagnosis of meningitis, and 175 children were not. INTERVENTIONS: None. METHODS: The emergency department chart and hospital records were reviewed for presenting demographic, historical, physical examination, and laboratory features. Clinical features of pretreated and untreated patients were compared. RESULTS: Pretreated children demonstrated less frequent temperature of 38.3 C or higher, altered mental status and a longer duration of symptoms before diagnosis, with more frequent vomiting; ear, nose, and throat infections; and physician visits in the week before detection of meningitis (P less than .05 for all comparisons). There was no difference in incidence of upper respiratory symptoms, seizures, nuchal rigidity, Kernig's and Brudzinski's signs, focal neurologic signs, mortality, and length of hospitalization between groups. CONCLUSION: Clinical features of children who have taken antibiotics before the detection of meningitis differ significantly from those who have not undergone antibiotic therapy. Physicians should be aware of these differences when evaluating young children on antibiotics for the possibility of meningitis.

Anti-Bacterial Agents↗
PubMed1992

Intravenous magnesium for acute asthma: failure to decrease emergency treatment duration or need for hospitalization.

STUDY OBJECTIVE: To evaluate the efficacy of routine early administration of i.v. magnesium to patients with acute asthma. DESIGN: Prospective, randomized clinical trial. SETTING: Urban teaching hospital emergency department. TYPE OF PARTICIPANTS: One hundred twenty consecutive patients aged 18 to 65 years with acute asthma unresponsive to a single albuterol treatment. INTERVENTIONS: All patients received oxygen, 125 mg i.v. methylprednisolone, and hourly albuterol inhalation therapy. The study group also received 2 g i.v. magnesium sulfate infused over 20 minutes. MEASUREMENTS AND MAIN RESULTS: Demographic and clinical characteristics were similar in both groups. Hospitalization was necessary in 13 of 58 patients who received magnesium (22%; 95% confidence intervals [CI], 13% to 32%) and 11 of 62 control patients (17%; 95% CI 10% to 26%; P = .523). Duration of ED treatment in discharged patients was 224 +/- 75 minutes in the magnesium group (95% CI, 208 to 240 minutes) and 228 +/- 90 minutes in the control group (95% CI, 209 to 247 minutes, P = .832). In addition, changes in peak expiratory flow were not statistically different. CONCLUSION: Routine early administration of IV magnesium in acute asthma does not alter treatment outcome.

Acute Disease↗
PubMed1992

Capsular injuries of the proximal interphalangeal joint.

Although capsular injuries of the PIP joints are common, their management is frequently complicated. Successful treatment must begin with a detailed history because reviewing the mechanism of injury may provide information relevant to the pathomechanics of the capsular disruption and facilitate making an accurate diagnosis. Grades I and II volar plate and collateral ligament sprains represent the vast majority of PIP joint injuries. They are best treated with a short period of dorsal splinting followed by supervised mobilization. Although splinting is also applicable for grade II sprains associated with instability and most grade III sprains, the initial period of immobilization should be longer. The prognosis for recovery is generally good, although some residual tenderness or joint stiffness are common complications. Dorsal capsular injuries, if unrecognized, result in deformity rather than instability. The majority of these injuries can also be treated by closed means, but they require more prolonged immobilization and more commonly result in reduced mobility than volar plate and collateral ligament injuries. Capsular injuries that are compound, irreducible, or associated with a large intraarticular fracture can result in serious problems. Frequently, these injuries require primary surgical treatment, particularly in the case of the irreducible dislocation, which always requires surgery. An exception to the generally poor prognosis of these injuries is the irreducible volar dislocation because the central tendon remains intact permitting early postoperative joint mobilization. A chronic dislocation or late instability are fortunately not common sequela of capsular injuries; however, when they do occur, surgery is required.

Finger Injuries↗
PubMed1991

Roles of metal ions in the maintenance of the tertiary and quaternary structure of arginase from Saccharomyces cerevisiae.

Arginase from Saccharomyces cerevisiae has long been known to be a metal ion-requiring enzyme as it requires heating at 45 degrees C in the presence of 10 mM Mn2+ for catalytic activation. Metals are also thought to play a structural role in the enzyme, but the identity of the structural metal and its precise structural role have not been defined. Analysis of the metal ions that bind to yeast arginase by atomic absorption spectroscopy reveals that there is a weakly associated Mn2+ that binds to the trimeric enzyme with a stoichiometry of 1.04 +/- 0.05 mol of Mn2+ bound per subunit and an apparent K'D value of 26 microM at pH 7.0 and 4 degrees C. A more tightly associated Zn2+ ion can only be removed by dialysis against chelating agents. In occasional preparations, this site contained some Mn2+; however, Zn2+ and Mn2+ together bind to high affinity sites with a stoichiometry of 1.14 +/- 0.25/mol of subunit. Both the loosely associated catalytic Mn2+ ion and the more tightly associated structural Zn2+ ion confer stability to the enzyme. Removal of the weakly bound Mn2+ ion results in a 3 degree C decrease in the midpoint of the thermal transition (T 1/2) (from 57 by 54 degrees C) as monitored by UV difference absorption spectroscopy. Removal of the tightly bound Zn2+ ion produces a 19 degrees C decrease in T 1/2 (to 38 degrees C). Similar results are obtained by circular dichroism measurements. When the Zn2+ ion is removed, the steady-state fluorescence intensity increases 100% as compared to the holoenzyme, with a shift in the emission maximum from 337 to 352 nm. This suggests that in the folded trimeric metalloenzyme, the tryptophan fluorescence is quenched and that upon removal of the structural metal, the quenching is relieved as tryptophan residues become exposed to more polar environments. Equilibrium sedimentation experiments performed after dialysis of the enzyme against EDTA demonstrate that arginase exists in a reversible monomer-trimer equilibrium, in the absence of metal ions, with a KD value of 5.05 x 10(-11) M2. In contrast, the native enzyme exists as a trimer with no evidence of dissociation when Mn2+ and Zn2+ are present (Eisenstein, E., Duong, L.T., Ornberg, R. L., Osborne, J.C., Jr., and Hensley, P. (1986) J. Biol. Chem. 261, 12814-12819). In summary, the study presented here demonstrates that binding of a weakly bound Mn2+ ion confers catalytic activity. In contrast, binding of a more tightly associated Zn2+ ion confers substantial stability to the tertiary and quaternary structure of the enzyme.

Arginase↗
PubMed1991

Differences and similarities between children, mothers, and teachers as informants on disruptive child behavior.

Prevalence rates of disruptive child behaviors, based on structured psychiatric interviews, are presented for samples of clinic-referred prepubertal boys at two sites to investigate differences and similarities among reports of the behaviors from children, parents, and teachers. Children reported significantly less hyperactive/inattentive and oppositional behaviors than either parents or teachers. In contrast, children did not differ from parents or teachers in their report on the prevalence of more serious conduct problems. These results were well replicated across two sites, despite the fact that there were significant differences between the sites in the level of hyperactive/inattentive child behaviors and conduct problems. The ranking of parents' and teachers' reported prevalence of specific child behavior problems in each of the three domains of disruptive behavior was strikingly similar. With one exception, the concordance between the prevalence ranking based on the children's reports was lower than that based on adults' reports, Children's reports on their own behavior did not predict various child handicaps 1 year later as well as did adults' reports. The results are discussed in relation to the usefulness of certain child behaviors in symptom lists for diagnostic purposes; the reliability of children's reports on their own behavior; and the possible reasons why prevalence rankings, as perceived by adults, are so similar.

Attention Deficit Disorder with Hyperactivity↗
PubMed1991

Stability of mothers' recall of the age of onset of their child's attention and hyperactivity problems.

The stability of mothers' recall of age of onset of attention deficit and hyperactive behaviors was assessed over a 1-year interval. The paper reports on which behaviors have the highest stability and the stability of a psychiatric diagnosis of attention deficit hyperactive disorder using different age cut-offs. The data showed a moderate degree of stability over a 1-year period, with school-related symptoms showing the least amount of change. An argument is made for keeping the current DSM-III-R diagnostic cut-off at age 6.

Attention↗
PubMed1991

Anxiety, inhibition, and conduct disorder in children: I. Relations to social impairment.

Jeffrey A. Gray has proposed a model in which conduct disorder (CD) is viewed as the result of both excessive activity of a behavioral activation system that mediates appetitive and aggressive behavior and deficient activity of a behavioral inhibition system that mediates both anxiety and the inhibition of behavior in the presence of cues signalling impending punishment or frustration. The relation of anxiety to antisocial behavior was examined in 177 clinic-referred boys, aged 7 to 12 years, 68 of whom met DSM-III-R criteria for CD. As predicted by Gray's model, boys with CD and comorbid anxiety disorder were markedly less impaired than boys with CD alone.

Aggression↗
PubMed1991

Plain abdominal radiography in the detection of acute medical and surgical disease in children: a retrospective analysis.

A retrospective review was performed to determine the utility of plain abdominal radiographs in evaluating children presenting to the emergency department. Clinical features, radiographic interpretation, and final diagnoses of 431 patients seen over one year were recorded. One hundred three (24%) patients had major diseases (ventriculoperitoneal shunt malfunction, foreign body ingestion, appendicitis, intussusception, bowel obstruction, necrotizing enterocolitis, toxic megacolon, blunt abdominal trauma, pyloric stenosis, and Hirschsprung's disease), while the remaining 328 (76%) had minor diseases. Radiographs were categorized as diagnostic, suggestive, normal, incidental, or misleading, with respect to the patient's final diagnosis. No single clinical feature was able to detect all diagnostic radiographs in patients with major diseases. Limiting radiographs to patients with prior abdominal surgery, suspected foreign body ingestion, abnormal bowel sounds, abdominal distention, or peritoneal signs identified all patients with radiographs diagnostic of a major disease while eliminating 48% of studies ordered. Our results suggest that restricting abdominal roentgenograms to patients with at least one of these features will detect most diagnostic radiographs in children with acute abdominal diseases.

Abdomen, Acute↗
PubMed1990

Steady-state fluorescence and time-resolved fluorescence monitor changes in tryptophan environment in arginase from Saccharomyces cerevisiae upon removal of catalytic and structural metal ions.

Yeast arginase is a trimeric protein of identical subunits, each containing three tryptophans. Time-resolved fluorescence and steady-state fluorescence were employed to monitor the effects of removing the weakly bound catalytic Mn2+ as well as the tightly bound structural Zn2+/Mn2+. Resolution of the total native emission spectrum into decay-associated spectra (DAS) yielded components with lifetimes of 0.1, 1.2, and 4.0 ns. Upon removal of the catalytic metal, the intensities increased approximately 20% while the lifetimes increased less than 10%, and the DAS were unchanged except in intensity. The two major components are well resolved, but the 0.1-ns term is small and dominated by scattered excitation. In contrast, removal of the structural metal increased decay times to 0.2, 1.8, and 5.3 ns. More important, both native DAS red-shifted and became indistinguishable. These data suggest that removal of the catalytic metal does little to change the microenvironments of the individual tryptophans while removal of the structural metal causes partial unfolding of the protein. The excitation spectra for the active and inactive trimers were resolved into their excitation DAS (IEDAS), suggesting ground-state heterogeneity of the fluorescent species. In contrast, the excitation spectra of arginase without the structural metal could not be resolved due to the indistinguishable DAS. The tryptophans are quenched by acrylamide but not by cesium or iodide. Global analysis of the acrylamide quenching data resulted in two quenching decay-associated spectra (QDAS) which correlated well with the DAS. Since the apoenzyme does not exhibit tryptophan accessibility to either positive or negative ionic quenchers, one must assume that the "unfolded" monomeric protein retains considerable tertiary structure.

Apoenzymes↗
PubMed1990

HIV-1 regulator of virion expression (Rev) protein binds to an RNA stem-loop structure located within the Rev response element region.

HIV-1 Rev protein, purified from E. coli, binds specifically to an RNA transcript containing the 223 nucleotide long Rev response element (RRE) sequence. Rev binds to RRE in vitro with an apparent dissociation constant of 1 to 3 nM as determined by filter binding, gel mobility shift assays, or an immunoprecipitation assay using a monoclonal antibody specific for the Rev C-terminus. Antisense RRE sequences are bound by Rev with a 20-fold lower affinity than wild-type RRE sequences. The Rev-RRE complex forms even in the presence of a 10,000-fold molar excess of 16S rRNA, whereas formation of the low affinity antisense RRE-Rev complex is efficiently blocked by addition of excess 16S rRNA. A approximately 33 nucleotide fragment is protected from ribonuclease T1 digestion by the binding of Rev to RRE RNA, suggesting that Rev binds with high affinity to only a restricted region of the RRE. This protected fragment is unable to rebind Rev protein but has been mapped to a 71 nucleotide long Rev binding domain sequence that overlaps the protected fragment.

Amino Acid Sequence↗
PubMed1990

The purification and characterization of arginase from Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, ornithine transcarbamoylase and arginase form a regulatory multienzyme complex (Hensley, P. (1988) Curr. Top. Cell. Regul. 29, 35-75). In this complex, arginase acts as a negative allosteric effector for ornithine transcarbamoylase. Before an analysis of the factors which promote and stabilize complex formation, arginase was purified in milligram quantities from a plasmid-containing, enzyme-overproducing, protease-deficient yeast strain and its physical characterization undertaken. The purified enzyme has a specific activity of 885 mumol urea min-1 mg-1 and a Km for arginine of 15.7 mM. The ultraviolet spectrum has a maximum absorbance at 279 nm, and the steady-state fluorescence emission spectrum has a maximum intensity at 337 nm, suggesting that the 3 tryptophans/polypeptide chain are in a relatively hydrophobic environment. Arginase has a weakly bound manganese responsible for the maintenance of the catalytic activity and is known to be heat activated in the presence of manganese. This effect is half-maximal at 12.1 microM manganese. In addition to a catalytic requirement for manganese, the presence of a more tightly bound metal is suggested from sedimentation studies. The native trimeric enzyme has a sedimentation coefficient of 5.95 S. Removal of the weakly associated metal results in no change in the sedimentation coefficient. However, dialysis with EDTA causes the s-value to decrease to 4.65 S, suggesting that under these conditions, the trimeric enzyme may partially dissociate. An analysis of CD spectra shows that significant spectral changes result from the removal of both the weakly bound metal and dialysis against EDTA.

Arginase↗