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Biomedical subjects

H Pirkle

Publications and source records attributed to H Pirkle.

At least 19 recordsLinked to original sources
PubMed1999

Crotalase, a fibrinogen-clotting snake venom enzyme: primary structure and evidence for a fibrinogen recognition exosite different from thrombin.

Crotalase, a fibrinogen-clotting enzyme isolated from the venom of Crotalus adamanteus, and its overlapping fragments were subjected to Edman degradation. The resulting amino acid sequence [see text] characteristic of a serine proteinase. Comparison with thrombin, the physiological fibrinogen-clotting enzyme, showed that thrombin's fibrinogen-recognition exosite (FRE) is poorly represented in crotalase. Hirudin, a FRE-dependent inhibitor, had no effect on crotalase. Spatial modeling of crotalase yielded a possible alternative fibrinogen-recognition site comprised of Arg 60F, Lys 85, Lys 87, and Arg 107 (underlined in the sequence above). Crotalase also lacks thrombin's YPPW loop, as well as its functionally important ETW 146-148, and its heparin-binding site. The enzyme contains a single asparagine-linked glycosylation site, NFT, bearing neutral and amino sugars that account for 8.3% of the enzyme's total molecular weight of 29,027. The calculated absorbance of crotalase at 280 nm, 1%, cm(-1) is 15.2.

Amino Acid Sequence↗
PubMed1990

Isoforms of a highly specific B beta-chain fibrinogenase from the venom of Crotalus atrox: preliminary observations.

Three variants of a Crotalus atrox venom enzyme that cleaves primarily the Arg42 - Ala bond of the B beta-chain of human fibrinogen were separated by high-performance liquid chromatography and were shown by N-terminal sequence analysis to be amino acid isoforms. All are single-chain glycoproteins whose approximate molecular weights lie between 26,000 and 28,000. The isoenzymes also cleaved the A alpha-chain at Arg491 - His, though much more weakly, with strengths for both bonds that varied among the isoforms.

Amino Acid Sequence↗
PubMed1989

Catroxobin, a weakly thrombin-like enzyme from the venom of Crotalus atrox. NH2-terminal and active site amino acid sequences.

Two thrombin-like isoenzymes, termed catroxobins, were purified by gel filtration and ion exchange chromatography to electrophoretic homogeneity from the venom of the Western diamondback rattlesnake, Crotalus atrox. By SDS-polyacrylamide gel electrophoresis their molecular weights were estimated to be 25,000 and 26,200. A 43-residue NH2-terminal sequence, containing the active histidine residue, was the same for the two isoenzymes. In addition, a 33-residue internal peptide from catroxobin I contained a normal active serine sequence. These sequences were highly homologous to other thrombin-like venom enzymes, and to pancreatic kallikrein and trypsin, but less so to the B chain of thrombin. Catroxobin, possessing 89 TAME esterase units/mg of protein, clotted human fibrinogen very slowly, releasing fibrinopeptide A and a small amount of fibrinopeptide B. No other evidence of cleavage of the fibrinogen molecule was revealed by polyacrylamide gel electrophoresis or HPLC.

Amino Acid Sequence↗
PubMed1989

On the location in the thrombin B chain of substrate recognition sites for fibrinopeptide release and factor XIII activation.

Thrombin, a serine proteinase comprised of two disulfide-linked subunits (A chain and B chain), induces clotting by releasing fibrinopeptide A from fibrinogen and then influences the character of the resulting fibrin by releasing fibrinopeptide B and by activating factor XIII. While the active center of thrombin is known to reside in its B chain, the subunit location of the structural determinants that govern the specific release of fibrinopeptides A and B and the activation of factor XIII have not been established. We have investigated the subunit location within the thrombin molecule of the determinants of substrate specificity for these actions using an isolated, immobilized B-chain preparation. Isolated B chain was prepared by covalently linking the intact thrombin molecule to Sepharose beads via the carbohydrate chain attached to asparagine 53 of its B chain, then reducing the single interchain disulfide bond to release the A chain, and finally reoxidizing the intrachain disulfide bonds of the immobilized B chain, allowing it to refold. The isolated, immobilized B chain of thrombin induced clotting of purified fibrinogen, releasing both fibrinopeptides A and B as demonstrated by HPLC and by electrophoresis of reduced fibrin chains. In addition, the B-chain preparation activated added factor XIII, yielding electrophoretically characteristic cross-linked fibrin chains.

Animals↗
PubMed1989

Lactate dehydrogenase isoenzyme composition of human platelets.

The LDH isoenzyme composition of 12 platelet preparations was determined by electrophoresis. The mean (+/- SD) percentages of LDH-1, LDH-2, LDH-3, LDH-4, and LDH-5 were 16.6 +/- 1.7, 30.1 +/- 1.0, 34.2 +/- 1.3, 18.2 +/- 1.3, and 0.9 +/- 1.1, respectively. In comparison with previous data, these data show identical ranking of the prevalence of each isoenzyme but significantly different percentages, particularly of LDH-1 and LDH-4. The release of platelet LDH by freezing and thawing differed little from that by homogenization.

Blood Platelets↗
PubMed1988

Hepatocellular carcinoma in hepatitis B surface antigen carriers in eight institutions.

We reviewed records of all persons dying between 1979 and 1986 in eight California institutions for the mentally retarded. Autopsies had been done in 71% of the 1,181 deaths. Nine deaths were due to hepatocellular carcinoma, which invariably developed in carriers of hepatitis B surface antigen (HBsAg) and was fatal within four months of diagnosis. The mean age at death was 32.7 years. The incidence of hepatocellular carcinoma in HBsAg carriers was 140 times greater than in the US population. Persistent hepatitis B infection was probably etiologically related to hepatocellular carcinoma in this population, which is relatively free of exposure to other hepatocarcinogens.

Adult↗
PubMed1986

Thrombin-like enzyme from the venom of Bitis gabonica. Purification, properties, and coagulant actions.

Gabonase, an enzyme which acts on fibrinogen and factor XIII in uniquely thrombin-like ways, was purified to electrophoretic homogeneity from the venom of Bitis gabonica. On sodium dodecyl sulfate-polyacrylamide electrophoresis, the reduced protein behaved as a single chain with Mr = 30,600. The enzyme contains 20.6% carbohydrate, no free sulfhydryl groups and hence, from amino acid analysis, five disulfide bonds. Its extinction coefficient (E1%1cm) at 280 nm is 9.6. Its pI is 5.3. Gabonase has an active serine residue, is inactivated by phenylmethanesulfonyl fluoride, and has an active histidine which reacts with the chloromethyl ketone of tosyl-L-lysine. Its NH2-terminal amino acid sequence (Val-Val-Gly-Gly-Ala-Glu-Cys-Lys-Ile-Asp-Gly-His-Arg-Cys-Leu-Ala-Leu-Leu -Tyr-) is homologous to the B chain of thrombin. The activity of the enzyme is stabilized by calcium ion. It exhibits strong N alpha-p-tosyl-L-arginine methyl esterase activity, hydrolyzes tripeptide nitroanilide derivatives weakly or not at all, and cleaves no peptide bonds in insulin, glucagon, or the S peptide of ribonuclease. Gabonase clots fibrinogen with a specific activity of 45 NIH thrombin-equivalent units/mg, releasing both fibrinopeptides A and B and showing substrate inhibition at fibrinogen concentrations of 3 mg/ml or greater. The enzyme also activates factor XIII. It is not inactivated by either heparin or hirudin.

Amino Acid Sequence↗
PubMed1985

Action of crotalase, an enzyme with thrombin-like and kallikrein-like specificities, on tripeptide nitroanilide derivatives.

Since crotalase has thrombin-like and kallikrein-like functional and structural properties, we compared the actions of crotalase, thrombin and plasma kallikrein on 13 tripeptide nitroanilide substrates. Initial rates of hydrolysis were determined at 27 degrees C, pH 8.3, and used to construct Lineweaver-Burk plots from which Km and Vmax were determined. The ratio of kcat/Km was taken as a measure of enzymatic specificity. Crotalase yielded kcat/Km values for the following nitroanilide substrates in descending order of magnitude: H-D-NLeu-CHA-Arg, H-D-Pro-HHT-Arg, Tos-Gly-Pro-Arg, H-D-PhGly-Phe-Arg, Cbo-Glu(BuO)-Gly-Arg, H-D-But-CHA-Lys, H-D-CHG-But-Arg, H-D-NLeu-HHT-Lys, H-D-HHT-Ala-Arg, Bz-Pro-Phe-Arg, Tos-Gly-Pro-Lys, MeS-Leu-Gly-Arg, MeO-CO-CHG-Gly-Arg. This pattern of specificity correlated only roughly with those of thrombin and kallikrein.

Chromogenic Compounds↗
PubMed1985

Modulation of red cell metabolism by states of decreased activation: comparison between states.

Marked decline of red cell metabolism has been described during the acute state of decreased activation associated with the stylized mental technique of transcendental meditation (TM) in long-term meditators (5-10 years regular elicitation, TM instructors). It is not known whether unstylized rest is accompanied by a similar effect and it is not known what effector(s) may contribute to red cell metabolic changes in these states. In the present study ordinary, unstylized rest was found to be accompanied by small increase of red cell glycolytic rate. Apparently, either repeated elicitation of TM behavior or some special feature of this practice become associated with new mechanisms of metabolic control than those previously in operation. Although the data of this study do not permit isolation of the precise psychological determinants of this effect, the range of possible physiological effectors can be delimited. Blood pH, PCO2, PO2, and phosphate can be eliminated as significant for red cell metabolic control during both TM and rest, and based upon related studies, several known hormones such as insulin, T3, T4, arginine vasopressin, oxytocin, prolactin and growth hormone can also be eliminated as responsible effector(s).

Acid-Base Equilibrium↗
PubMed1983

Metabolic control in a state of decreased activation: modulation of red cell metabolism.

Very little is known in depth of the biochemical and physiological changes induced at the cellular level by human behavioral states. For study of the physiology of behavior at this level, the erythrocyte may be useful, because it is readily available and its metabolism and metabolic control are comparatively well understood. In this report we describe a marked decline of red cell glycolytic rate induced by the transcendental meditation technique (TM). This decline was significantly correlated with decreased plasma lactate concentration and with relaxation as indicated by electrodermal response. The occurrence of sleep was not correlated with the metabolic changes. The observed lack of variation of blood pH, blood gases, glucose, and hematocrit in this behavior implies that the decrease of erythrocyte metabolism is not an epiphenomenon of respiratory change or substrate availability. Based upon further measurements indicating persisting alteration of the red blood cell, we suggest the possibility of attachment of a humoral agent(s) to the cell in the mechanism of this effect. This behavioral effect is unique, and the effector(s) responsible may increase our understanding of metabolic control of the erythrocyte and of TM.

Aerobiosis↗
PubMed1983

Fibrinogen Seattle releases half the normal amount of fibrinopeptide B.

Fibrinogen Seattle, a clinically silent, slow-clotting dysfibrinogen, releases 50% of the normal amount of fibrinopeptide B as assessed by amino acid analysis. The reduced dysfibrin exhibited equal quantities of chains with B beta- and beta-charge mobility on polyacrylamide gel electrophoresis in 2 M urea at low pH. By these same techniques, the release of fibrinopeptide A was normal. Clots formed by repolymerizing the thrombin and batroxobin dysfibrin monomers showed a maximal turbidity that was lower than normal. Fibrinogen Seattle was indistinguishable from normal fibrinogen by radial immunodiffusion and immunoelectrophoresis. Degradation by plasmin and transamination by factor XIIIa were normal. The characteristics of fibrinopeptide release by fibrinogen Seattle distinguish it from other reported dysfibrinogens.

Amino Acids↗
PubMed1982

Kallikrein-like activity of crotalase, a snake venom enzyme that clots fibrinogen.

During the amino acid sequence determination of crotalase (EC 3.4.21.30), the thrombin-like enzyme from the venom of Crotalus adamanteus (eastern diamondback rattlesnake), we found that, in addition to the expected structural homology with bovine thrombin (EC 3.4.21.5), there was even greater homology with porcine pancreatic kallikrein (EC 3.4.21.8). In exploring further the similarities between crotalase and kallikrein, several striking observations were made. First, crotalase was rapidly and specifically inhibited by the tripeptide affinity labeling derivative prolylphenylalanylarginine chloromethyl ketone, which is known to be a specific inhibitor of kallikrein. Second, NaDodSO4/acrylamide gel electrophoresis revealed that crotalase cleaves the plasma kallikrein-susceptible bonds in human high molecular weight kininogen, producing an intermediate with procoagulant activity. Crotalase-catalyzed cleavage of high molecular weight kininogen also liberates kinin as evidenced by rat blood pressure bioassay. Finally, crotalase exhibits substrate specificity not only for the thrombin chromogenic substrate S-2238 but also for the kallikrein substrates S-2302 and S-2266. Interestingly, one of the other reactions catalyzed by plasma kallikrein, the activation of plasminogen, was not one of the activities exhibited by crotalase.

Animals↗