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D W Green

Publications and source records attributed to D W Green.

At least 73 records · Page 4Linked to original sources
PubMed1992

Integration of a personal computer workstation and radiology information system for obstetric sonography.

A personal computer workstation has been developed for storage and analysis of obstetric sonographic examinations. The workstation also serves as an interactive data terminal for our radiology information system. A data-base management program locally stores quantitative and descriptive sonographic results. Algorithms are used to analyze growth parameters over serial examinations, plot growth curves, generate a radiologic report, and provide instantaneous diagnostic assistance and suggestions. A bibliographic data-base system containing more than 3000 references (with abstracts) in the obstetric sonographic literature is integrated with the software's analytical functions. A telecommunications software module performs dialogues, such as immediate automatic transcription of the sonographic report, with the radiology information system. An examination summary form, growth curves, and the radiologist's report can be printed or digitally faxed by the workstation after authorization by the radiologist. The workstation has improved the organization of sonographic data, facilitated serial quantitative analysis, supplemented educational resources for our staff radiologists and residents, reduced transcription errors and transcription delays, and shortened to minutes the time necessary to deliver precise examination results to clinicians. This model is suitable for use in many areas in a radiology department.

Female↗
PubMed1991

Catalysis by yeast alcohol dehydrogenase.

Table 7 presents a brief summary of the effects of various mutations on some of the relevant kinetic constants. The results illustrate several important features of the use of site-directed mutagenesis in exploring structure and function of enzymes. Note that most of the mutations affect a given step or kinetic parameter in the mechanism, such as the binding of NAD+ or the turnover number with ethanol. Furthermore, one mutation can affect many steps in the mechanism. Thus, it is difficult to ascribe a particular role to an amino acid residue. It is also difficult to quantify the function of a residue, since the magnitudes of the effects on kinetic parameters will be modulated by the other amino acid residues that participate in the reaction. Comprehensive and quantitative kinetic studies of many mutant enzymes are required if we are to understand catalysis and specificity. We are reluctant to describe any residue as "essential" for activity since substitution with some amino acid can probably produce an enzyme with some residual activity. (Maybe the Thr48Gly enzyme would be active, as a water molecule could substitute for the hydroxyl of the threonine.) Likewise, when substitution of a residue partially, but not totally, decreases activity, it does not necessarily mean that the residue is "not essential". The change in activity can reflect the contribution of that residue to catalysis. On the other hand, if various substitutions of a residue do not change activity, it would be reasonable to conclude that the residue is not essential (Plapp et al., 1971). Most of the amino acid residues at the active site are involved in the catalytic mechanism, either by contacting the substrates directly or by participating in the chemistry. Some of the residues that are outside of the active site are indirectly involved, by affecting the structure of the protein. Substitution of an important amino acid residue should significantly affect activity, and studies on the kinetics and structure should allow one to distinguish among the various explanations.

Alcohol Dehydrogenase↗
PubMed1990

Substrate specificity of recombinant human renal renin: effect of histidine in the P2 subsite on pH dependence.

Steady-state kinetic analysis of human renin demonstrates the histidine proximal to the substrate scissile peptide bond contributes to the unique specificity and pH dependence of this aspartyl protease. Recombinant human renal renin purified from mammalian cell culture appears to be indistinguishable from renin isolated from human kidney with respect to specific activity (1000 Goldblatt units/mg). Recombinant renin contains carbohydrate covalently attached to asparagines at positions 5 and 75 (renin numbering) and disulfide linkages at Cys-51/Cys-58, Cys-217/Cys-221, and Cys-259/Cys-296. Renin pH dependence was evaluated between pH 4.0 and 8.0 by using a synthetic substrate identical with the amino terminus of porcine angiotensinogen (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu*Leu-Val-Tyr-Ser, where the asterisk indicates the scissile peptide bond and the proximal histidine is in italics) and an analogous tetradecapeptide where the proximal histidine was substituted with glutamine. Comparison of the pH profiles shows the catalytic efficiency (V/Km) and maximal velocity (V) of renin are greater above pH 6.5 with the substrate containing histidine proximal to the scissile peptide bond, but below pH 5.0 these parameters are greater with the glutamine substrate analogue. Solvent isotope effects show that proton transfer contributes to the rate-limiting step in catalysis with both substrates and that the proximal histidine does not serve as a base in the catalytic mechanism. Molecular modeling indicates the substrate histidine could hydrogen bond to Asp-226 of the enzyme (renin numbering), thus perturbing the ionization of the catalytic aspartyl groups (Asp-38 and Asp-226).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Reduced cholecystokinin mediates the inhibition of pancreatic growth induced by bile salts.

The effects of luminal bile salts on plasma levels of cholecystokinin (CCK) and growth of the pancreas in mice were studied. Nonfasting levels of plasma CCK in control mice were 8.1 +/- 1.5 pM. Feeding mice a 0.5% (wt/wt) sodium taurocholate-supplemented diet for 1 wk significantly lowered nonfasting levels of plasma CCK to 4.1 +/- 0.5 pM and decreased the total contents of pancreatic DNA by 22%, RNA by 25%, and protein by 24%. All of the inhibitory effects of taurocholate on pancreatic growth were completely reversed by the simultaneous administration of CCK-8 (3 micrograms/kg, 3 times daily). In contrast, intraluminal neutralization of endogenous bile salts by feeding a 4% (wt/wt) cholestyramine-supplemented diet for 1 wk significantly elevated nonfasting levels of plasma CCK to 14.7 +/- 1.5 pM and increased the total contents of pancreatic DNA by 34%, RNA by 40%, and protein by 35%. All of the stimulatory actions of cholestyramine on pancreatic growth were completely abolished by the administration of the highly potent and specific CCK-receptor antagonist L364,718 (1 mg/kg, twice daily). These findings, therefore, indicate that bile salts appear to play a physiological role in pancreatic growth by regulation of plasma levels of CCK.

Animals↗
PubMed1990

Protective action of luminal bile salts in necrotizing acute pancreatitis in mice.

Bile salts in the intestinal lumen act to inhibit the release of cholecystokinin (CCK). Recent studies have shown that CCK may play a permissive role in the development of acute pancreatitis. In this study, the amount of luminal bile salts in female Swiss Webster mice was either decreased by feeding 4% (wt/wt) cholestyramine or increased by feeding 0.5% sodium taurocholate for 1 wk. Plasma levels of CCK were stimulated by cholestyramine and inhibited by taurocholate. Then, acute pancreatitis was induced either by caerulein injections, or by feeding a choline-deficient, ethionine-supplemented (CDE) diet. Feeding of cholestyramine significantly decreased survival from 25% to 0% in the CDE pancreatitis, and increased the magnitude of elevation of serum amylase levels and the extent of pancreatic necrosis in both models of pancreatitis; CCK-receptor blockade with CR-1409 completely abolished the adverse effects of cholestyramine. In contrast, feeding of taurocholate significantly increased survival to 100% and decreased the elevation of serum amylase and pancreatic necrosis; CCK-8 antagonized these actions of taurocholate. Luminal bile salts appear to provide a physiologic protection against necrotizing pancreatitis, at least in part, both by inhibiting the release of CCK and by promoting resistance of the pancreas to CCK excessive stimulation in vivo.

Acute Disease↗
PubMed1989

Mesoatrial shunt: a surgical option in the management of the Budd-Chiari syndrome.

The Budd-Chiari syndrome, arising from hepatic venous outflow obstruction, is frequently complicated by inferior vena caval occlusion or obstruction. Satisfactory decompression of the liver by either portacaval or mesocaval shunts may therefore prove impossible or be prone to failure from shunt thrombosis. The mesoatrial shunt which allows the portal vein to drain directly into the right atrium has previously been advocated in this situation. Five patients with the Budd-Chiari syndrome and caval occlusion and/or obstruction have had mesoatrial shunts constructed using externally supported polytetrafluoroethylene grafts. A single thoracoabdominal incision, incorporating a median sternotomy, was found to provide a satisfactory approach. All patients recovered well with resolution of ascites, diminution in liver size and improvement in inferior vena caval pressure gradients. Furthermore, all shunts have remained patent, as determined by Doppler flow studies and contrast-enhanced computed tomographic scanning, during follow-up periods ranging from 9 to 16 months. If these results are supported by longer term studies, the mesoatrial shunt may become the surgical treatment of choice in patients with hepatic vein occlusion and the Budd-Chiari syndrome associated with inferior vena caval obstruction.

Adolescent↗
PubMed1989

Gastrointestinal peptides.

The intent of this article is to summarize the primary structures (that is, amino acid sequences) localization, primary gastrointestinal and pancreatic actions, and possible clinical relevance of the major gut peptides as well as some of the miscellaneous gut peptides. A brief overview of the general characteristics of gut peptides is presented.

Digestive System Physiological Phenomena↗
PubMed1987

Kinetic characterization of yeast alcohol dehydrogenases. Amino acid residue 294 and substrate specificity.

A three-dimensional model of yeast alcohol dehydrogenase, based on the homologous horse liver enzyme, was used to compare the substrate binding pockets of the three isozymes (I, II, and III) from Saccharomyces cerevisiae and the enzyme from Schizosaccharomyces pombe. Isozyme I and the S. pombe enzyme have methionine at position 294 (numbered as in the liver enzyme, corresponding to 270 in yeast), whereas isozymes II and III have leucine. Otherwise the active sites of the S. cerevisiae enzymes are the same. All four wild-type enzymes were produced from the cloned genes. In addition, oligonucleotide-directed mutagenesis was used to change Met-294 in alcohol dehydrogenase I to leucine. The mechanisms for all five enzymes were predominantly ordered with ethanol (but partially random with butanol) at pH 7.3 and 30 degrees C. The wild-type alcohol dehydrogenases and the leucine mutant had similar kinetic constants, except that isozyme II had 10-20-fold smaller Michaelis and inhibition constants for ethanol. Thus, residue 294 is not responsible for this difference. Apparently, substitutions outside of the substrate binding pocket indirectly affect the interactions of the alcohol dehydrogenases with ethanol. Nevertheless, the substitution of methionine with leucine in the substrate binding site of alcohol dehydrogenase I produced a 7-10-fold increase in reactivity (V/Km) with butanol, pentanol, and hexanol. The higher activity is due to tighter binding of the longer chain alcohols and to more rapid hydrogen transfer.

Alcohol Oxidoreductases↗
PubMed1987

Structure and function in yeast alcohol dehydrogenases.

The structure and kinetics of the isozymes from Saccharomyces cerevisiae (ADH I, II, III) have been compared, and the ADH I gene was specifically mutagenized in order to substitute amino acid residues of particular interest. A model of the yeast enzyme was constructed on the basis of the structure of the homologous horse liver enzyme. Steady state kinetic studies, at pH 7.3 and 30 degrees C, showed that the enzymes follow the Ordered Bi Bi mechanism. ADH II has a Michaelis constant for ethanol that is 10-fold smaller than the constants found for ADH I or III. Replacement of Met-294 (liver numbering) in the substrate binding pocket of ADH I with Leu, as found in ADH II, could be responsible for the different kinetics. However, the mutant enzyme, ADH I-Leu, had constants with ethanol that were similar to those of ADH I. Nevertheless, the Leu enzyme had better catalytic activity with longer chain alcohols than did the Met enzyme. Other substitutions must account for the differences between ADH I and II. His-47 binds the pyrophosphate of coenzyme, and replacement with Arg (as in the liver enzyme) decreases turnover numbers by 6-fold and dissociation constants for NAD+ and NADH by only 2 to 4-fold. The lower turnover number explains why yeast harboring the mutant Arg enzyme are resistant to poisoning by allyl alcohol. ADH I and ADH I-Arg have maximal activity on ethanol at pH values above a pK of about 7. Replacement of His-51 with Gln reduces activity 12-fold and abolishes the pK value.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol Dehydrogenase↗
PubMed1986

Control, activation, and resource: a framework and a model for the control of speech in bilinguals.

This paper proposes a framework for examining the way in which bilinguals control the use of their two languages. In so doing it seeks to extend current functional descriptions of language production and to provide a single scheme in which both normal and pathological performance can be understood. Within the overall framework a specific model is developed. It is compatible with current findings, makes predictions about the performance of normal as well as brain-damaged bilinguals, and explains some previously puzzling findings.

Aphasia↗