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B F Gibbs

Publications and source records attributed to B F Gibbs.

71 records · Page 4Linked to original sources
PubMed1992

Conformationally restricted thrombin inhibitors resistant to proteolytic digestion.

A new type of thrombin exo-site inhibitor has been designed with enhanced inhibitory potency and increased metabolic stability. With the aid of the model of the structure of the thrombin-hirudin fragment complex [Yue, S.-Y., DiMaio, J., Szewczuk, Z., Purisima, E. O., Ni, F., & Konishi, Y. (1992) Protein Eng. 5, 77-85], cyclic analogs of the hirudin fragment (hirudin55-65) were designed and synthesized. In these analogs, the side chains of appropriately substituted residues, 58 and 61, were joined in order to restrict the conformation of the inhibitor. An analog with an 18-membered lactam ring showed higher antithrombin activity (IC50 = 0.57 microM) than the corresponding analogs with 17- or 16-membered rings and was 2-fold more potent than its linear counterpart. Even 4-fold greater enhancement was obtained when a shorter fragment, hirudin 55-62, was cyclized. This cyclization not only improved the potency but, more importantly, dramatically increased the resistance to proteolytic digestion. Remarkable enhancement of stability to proteolysis was observed for peptide bonds located in the exocyclic linear peptide segments. These results are discussed using molecular modeling.

Amino Acid Sequence↗
PubMed1990

Purification and characterization of two distinct lipases from Geotrichum candidum.

Lipase, an enzyme that hydrolyzes triacylglycerol, has been purified and characterized. The purification procedure includes ethanol precipitation and chromatographies on Sephacryl-200 HR, high resolution anion-exchange (mono Q) and Polybuffer exchanger 94. With this procedure, two forms of lipases from Geotrichum candidum were obtained. Lipase I (main enzyme) and lipase II (minor enzyme) were purified 35-fold with a 62% recovery in activity and 94-fold with a 18% recovery in activity, respectively. Their molecular weights have been estimated by polyacrylamide gel electrophoresis under denaturing conditions and by molecular sieving under native conditions at 56,000. Lipase I and II had optimum pH values of 6.0 and 6.8 and isoelectric points of 4.56 and 4.46, respectively. The enzymes are stable at a pH range of 6.0 to 8.0. Monovalent ions had little effect on both enzyme activities, while divalent ions at concentrations above 50 mM inhibited the lipase activities in a concentration-dependent manner. Sodium dodecyl sulfate at a concentration lower than 10 mM completely inhibited the lipase activity.

Amino Acids↗
PubMed1990

Recovery of biosurfactants by ultrafiltration.

Ultrafiltration was used in a one-step method to purify and concentrate biosurfactants--surfactin and rhamnolipids--from culture supernatant fluids. The ability of surfactant molecules to form micelles at concentrations above the critical micelle concentration allows these aggregates to be retained by relatively high molecular weight cut-off membranes. Lower molecular weight impurities such as salts, free amino acids, peptides and small proteins are easily removed. Various molecular weight cut-off membranes were examined for the retention of surfactin and rhamnolipids (mol. wts 1036 and 802 respectively). Amicon XM 50 was the superior membrane for retention of surfactin and a 160-fold purification was rapidly achieved. The YM 10 membrane was the most appropriate for rhamnolipid recovery. Ultrafiltration can play an important role in biosurfactant purification as large volumes of media can be processed rapidly at extremely low cost.

Amino Acid Sequence↗
PubMed1989

Carotid endarterectomy in community practice: surgeon-specific versus institutional results.

The efficacy of carotid endarterectomy in preventing stroke is clearly related to appropriate patient selection and low surgical morbidity and mortality. It has been suggested that since results at some centers are better than nationwide statistics, perhaps the operation should be limited to those institutions. In this paper we present an experience with carotid endarterectomy over the past twelve years. These 566 consecutive cases were performed by two vascular surgeons in a large metropolitan area using thirteen different hospitals ranging from 150 to 500 beds. Our mortality of 0.5% and permanent stroke incidence of 1.6% did not vary significantly from hospital to hospital. Where the results of surgical audits were available from the individual hospitals, the overall complication rates were significantly higher. We conclude that individual surgeons, not institutions, determine the efficacy of carotid endarterectomy in community practice.

Adult↗
PubMed1989

Correlation of nitrogen metabolism with biosurfactant production by Pseudomonas aeruginosa.

A direct relationship between increased glutamine synthetase activity and enhanced biosurfactant production was found in Pseudomonas aeruginosa grown in nitrate and Proteose Peptone media. A chloramphenicol-tolerant strain showed a twofold increase in biosurfactant production and glutamine synthetase activity. Increased ammonium and glutamine concentrations repressed both phenomena.

Agar↗
PubMedDate not supplied

Beta-endorphin in pituitary intraglandular colloid of intermediate lobe origin.

Radioimmunoassay (RIA) detected the presence of beta-endorphin in the intraglandular colloid (IGC) of bovine pituitary intermediate lobe origin. The amount of beta-endorphin recovered in each of twelve samples ranged from 0.15 to 218.30 pmol/mg protein. A second group of assays [amino acid analysis, high performance liquid chromatography (HPLC) and mass spectral analysis] confirmed the RIA findings in another series of colloid samples. Approximately 75 pmol was collected from eight pooled glands. beta-Endorphin is an addition to the list of peptide hormones (e.g., methionine-enkephalin, adrenocorticotropin, arginine-vasopressin, alpha-melanocyte-stimulating hormone, beta-lipotropin and somatostatin) previously discovered in IGC by this laboratory.

Amino Acid Sequence↗
PubMedDate not supplied

Derivatization of yeast cytochrome c peroxidase with pentaammineruthenium(III).

Cytochrome c peroxidase (CCP) was derivatized using aquopentaammineruthenium(II) [a5RuIIH2O] resulting in stable, covalently-linked derivatives that were purified by cation-exchange FPLC. Spectrophotometric determination of a5RuHis:heme ratios allowed identification of two derivatives containing one a5RuHis per CCP molecule. The histidine-specific reagent, diethyl pyrocarbonate (DEPC), which reacted with three histidine residues in native CCP (6, 60, 96) at pH 7, reacted with only two histidines in both a5RuHisCCP species. X-ray crystallography showed that a5Ru is coordinated to His60 in one derivative [Fox et al. (1990) J. Am. Chem. Soc. 112, 7426]; HPLC and mass spectral analysis of the tryptic peptides of the other derivative identified a peptide (MW = 1469 Da) corresponding to residues 1-12 of CCP plus a5Ru, indicating His6 as the site of modification. Mass spectral analysis of native CCP, a5RuHis60CCP, and the a5RuHis6 derivative yielded MWs of 33,536, 33,717, and 33,901 Da, respectively, revealing that a second site is ruthenated in the His6 derivative. Mass spectral analysis of a shoulder separated from the a5RuHis60CCP FPLC peak also indicated the presence of CCP with bound a5Ru (MW = 33,718 Da). Differential pulse voltammetry of this shoulder, which has negligible a5RuHis absorption, gave a peak at -68 mV (vs NHE) which is in the range expected for reduction of a5RuIII (carboxylato) complexes, as well as a peak at 42 mV due to the presence of approximately 20% a5RuHis60CCP. The extent of ruthenation at sites other than histidine was unexpected and illustrates that a5RuIIH2O is less specific for histidine than previously thought. Activity measurements and stability of enzyme intermediates were measured to further characterize the a5RuCCP species and showed that the derivatives have similar properties to native CCP.

Amino Acid Sequence↗
PubMedDate not supplied

Heterogeneity of signal transduction mechanisms in human basophils and human skin mast cells. II. Effects of 7-O-methyl-UCN-01, NPC 15437 and bryostatin 1 and 2, four protein kinase C-modulatory agents, on mediator release.

Basophils and mast cells play a crucial role in immunological and allergic processes due to the release of inflammatory mediators such as histamine. It has been suggested for a long time that the histamine release (HR) from these cells is closely related to protein kinase (PKC) activity. However, the distinct role of PKC with its large variety of isozymes in different cell types and the actions of these isozymes in HR still remain unclear. Therefore, in the present study, we compared the effects of the two PKC inhibitors 7-O-methyl-UCN-01 (UCN-01-Me) and NPC 15437 as well as two PKC activators, bryostatin 1 and 2, on anti-IgE and Ca(2+)-ionophore-induced HR from human basophils and isolated human skin mast cells (HSMC). In both HSMC and basophils, anti-IgE-induced HR was inhibited by PKC inhibitor UCN-01-Me pre-incubation dose-dependently. In stark contrast, A23187-induced HR was unaffected by UCN-01-Me in both cell types. In our experiments, the inhibitory efficacy of the compound NPC 15437 on HR was much lower than that of UCN-01-Me and showed no statistical significance. Both bryostatins 1 and 2 produced good dose-dependent inhibition of HR from HSMC stimulated with anti-IgE, whereas HR from basophils was potentiated with these compounds. The same effects were observed with basophils stimulated with A23187, where potentiation of HR was up to fourfold of the control at the highest concentrations of bryostatins, while HSMC showed a slight decrease in HR compared to non-bryostatin-treated controls. Basophils and HSMC showed very clear differences in HR when directly stimulated with the bryostatins, since no HR was observed from HSMC while in basophils the HR increased up to 47% of total histamine at the highest concentrations of bryostatins (1 mumol/l). HR from basophils was observed to be strictly dose-dependent. The differences in the cell reactions of the two cell types incubated with these four compounds indicate distinct biochemical roles of PKC in the cascades leading to degranulation of the cells. Furthermore, the experiments with UCN-01-Me support the hypothesis of PKC-beta to play a substantial positive modulatory role for the degranulation of immunologically stimulated basophils.

Alkaloids↗