Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.4.21.1 (chymotrypsin)
10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The possible participation of proteases in human platelet aggregation was explored using various protease inhibitors and substrates. Protease inhibitors used included naturally occurring inhibitors of serine proteases and synthetic inhibitors that modify the active site of protease. Substrates used were synthetic substrates for the trypsin type as well as for the chymotrypsin type of protease. All these inhibitors and substrates inhibited platelet aggregation and serotonin release induced by ADP, collagen, epinephrine, or thrombin. In ADP- and epinephrine-induced platelet aggregation the second phase of aggregation was most efficiently inhibited. The inhibitors suppressed the formation of malondialdehyde during platelet aggregation. Release by aggregating agents of arachidonate and its metabolites from indomethacin-treated platelets as well as nontreated platelets was also inhibited. The inhibitors apperar to interact with stimulated platelets but not with unstimulated platelets. These observations suggest that the interaction of an aggregating agent with its platelet receptor activates a unique precursor serine protease that in turn activates platelet phospholipase to liberate arachidonic acid (the precursor of the potent platelet aggregating agent thromboxane A2) from platelet phospholipids.
...
PMID:Inhibition of platelet aggregation by protease inhibitors. Possible involvement of proteases in platelet aggregation. 65 19

Human alpha thrombin acts as a mitogen for cultures of resting chick embryo fibroblasts (CEF) in serum free medium. The use of 125I-labeled thrombin shows that thrombin specifically binds to CEF and that after a lag of approximately 30 to 60 minutes it can not be removed by subsequent exposure to trypsin. The entry of 125I thrombin into the trypsin-insensitive domain is not inhibited to any great extent by excess unlabelled thrombin. The cell-associated thrombin retains its native molecular weight and its catalytic activity toward synthetic amide substrates. It appears to be located in the crude nuclear fraction of homogenized CEF cells. The association of thrombin with CEF is specific, since the non-mitogenic serine protease chymotrypsin is internalized to a much lesser extent than thrombin. The data are discussed in terms of a possible intracellular site for thrombin's mitogenic action.
...
PMID:Binding and internalization of 125I thrombin in chick embryo fibroblasts: possible role in mitogenesis. 67 Mar 1

Low salt extracts from homogenates of bovine cardiac muscle contain two protease inhibitors, one specific for the calcium-activated protease from this tissue and the other for trypsin and chymotrypsin, but no other serine proteases, including plasmin, thrombin, and subtilisin. The former, which can be separated from the protease by chromatography on DEAE-cellulose, is a protein with a molecular weight of 270,000. Its action is not based on the sequestering of calcium, and it is present in large excess over the amount of calcium-activated protease in this tissue. The trypsin inhibitor, which has a molecular weight of 70,000, is estimated to be present at approximately 300 microgram/g, wet weight, of tissue. The identification of inhibitors such as these in the cytoplasm may explain why nonlysosomal proteolytic activity has been thought to be insignificant in the overall turnover of intracellular protein and suggests that a re-evaluation of this possibility is necessary.
...
PMID:Identification of two protease inhibitors from bovine cardiac muscle. 68 25

The amino-acid sequence of the heavy chain of bovine blood coagulation factor X1 (Stuart factor) isolated before and after activation has been determined. Sequence analysis was performed on fragments obtained by cleavage with cyanogen bromide and by tryptic digestion. Comparison of the complete sequence with those of other hepatic and pancreatic serine proteases demonstrates homology of the heavy chain of activated factor X1 (factor X1a) with the B chain of bovine thrombin as well as with bovine trypsin, chymotrypsins A and B, and porcine elastase. The activation peptide cleaved near the amino terminus by a protease from Russell's viper venom differs in both size and sequence from those of other serine proteases. With three exceptions, all of the residues which are important in the catalytic functions of trypsin and chymotrypsin occur in corresponding loci in the heavy chain of factor Xa. These finding suggest that the three-dimensional structure of the heavy chain is similar to that of the pancreatic serine proteases and that these enzymes have evolved from a common ancestral gene.
...
PMID:Bovine factor X1 (Stuart factor): amino-acid sequence of heavey chain. 105 93

The mechanism of stimulation of platelets by thrombin and other proteases was studied by following kinetics of secretion of Ca2+ or ATP. The progress-time curves of secretion were analyzed for rate and total amount released. The reaction of thrombin was perturbed by addition of hydroxylamine or a competitive inhibitor and by variation of pH and it was compared with the reactions of other proteases. Trypsin and papain, with specificities for arginyl residues, induced secretion with a time course that was nearly identical with that induced by thrombin when saturating levels of enzyme were used. At low levels of enzyme, trypsin and papain gave extended lags in the progress-time curves. Higher concentrations of trypsin and papain were required for saturation of the measured parameters. Human plasmin (lysly specificity) and bovine chymotrypsin (aromatic amino acid specificity) failed to induce platelet secretion. Active site inhibited thrombin was also ineffective. Both yield and kinetics depended on pH, with the pH profile for each enzyme similar to its profile for hydrolysis of synthetic substrates. Studies at low pH also showed that the early part of the reaction undergoes a change in rate-determining step from enzyme dependent at low enzyme to enzyme indepdenent at high enzyme. Hydroxylamine, a nucleophile that would be expected to accelerate hydrolytic reactions, actually decreased both the rate of initial reactions and yield. A competitive inhibitor of thrombin also decreased both rate and yield; a calculated inhibition constant was in agreement with the value for a synthetic substrate, suggesting that the interaction of thrombin with platelets is analogous to reaction with substrates. A modification of our previous model is proposed in order to accommodate the results described here and to reaoncile the apparent contradictions that enzyme was found not to turn over in the reaction (Detwiler, T. C., and Feinman, R. D. (1973), Biochemistry 12, 282), that catalytic activity is required (Davey, M. G., and Luscher, E. F. (1967), Nature (London) 216, 875; this paper), and that the reaction is characterized by an apparent equilibrium binding (Tollefsen, D. M., Feagler J. R., and Majerus, P. W. (1974), J. Biol. Chem. 249, 2646). The essential feature is a reversible catalytic step with no dissociation of enzyme from product. This is followed by irreversible, thrombin-independent platelet processes leading to secretion, with yield dependent on the equilibrium concentration of the thrombin product. The model thus has aspects of catalysis, stoichiometry, and an agonist-receptor equilibrium.
...
PMID:Platelet stimulation by thrombin and other proteases. 116 69

Factor XIII is present in plasma as a proenzyme, which when activated catalyses the formation of epsilon(gamma-glutamyl)lysyl bonds in fibrin. In this study the activation of purified plasma factor XIII was examined quantitatively with the fluorescent amine incorporation assay. Activation products were examined by polyacrylamide gel electrophoresis. The serin proteases, thrombin, trypsin, chymotrypsin, and factor Xa, and also Reptilase were tested for their ability to activate factor XIII. Highly purified thrombins activated purified factor XIII; this reaction was not calcium dependent. Trypsin was also a potent activator, but no transglutaminase activity was found with chymotrypsin. The most highly purified preparations of Reptilase had no effect on factor XIII activity. Less purified Reptilase preparations activated factor XIII, which suggests the presence of another enzyme in these Reptilase preparations. Highly purified factor Xa was found to be an effective activator of purified factor XIII. In contrast to thrombin activation, this reaction required calcium. It may be that under certain circumstances factor XIIIa could be formed in vivo directly by the alternative pathway of factor Xa. Factor XIIIa could then crosslink fibrinogen, which would also provide an alternative pathway for thrombus formation. Also, the activation of factor XIII by both factor Xa and thrombin provides a further point of control in the blood coagulation process.
...
PMID:Alternative pathways for the activation of factor XIII. 120 Dec 28

Mouse saliva contains a potent inhibitor of complement activity. The secretion of this inhibitor appears to be regulated by action on alpha-adrenergic receptors for two reasons. First, an alpha-agonist (norepinephrine) elicited saliva with a 260-fold higher specific activity of the inhibitor than that obtained with a cholinergic agent (pilocarpine). Second, the alpha-agonist elicited saliva having 43-foldgreater specific activity than that obtained following administration of a beta-adrenergic agonist (isoproterenol). This anticomplementary factor probably proteolytically degrades one or more of the complement components since it is inhibited by several protease inhibitors. The salivary anticomplementary factor is more potent than trypsin, chymotrypsin, thrombin, or Kallikrein. The anticomplementary factor has a pattern of inhibition like that of Kallikrein but unlike those of trypsin or chymotrypsin.
...
PMID:Alpha-adrenergic regulation of the secretion of an anticomplementary factor in mouse saliva. 126 87

Bovine plasma factor V has been isolated by a preparative procedure involving barium sulfate adsorption, QAEC extraction, poly(ethylene glycol) precipitation, and finally chromatography on a desulfated Sepharose 6B column. Factor V was recovered as a single peak in yields of 35-40% with a specific activity of 50-70 representing a purification of 1000-2000-fold relative to the starting plasma. The apparent molecular weight of the purified factor V was 439,000 +/- 5000. On sodium dodecyl sulfate gel and analytical gel electrophoresis, this factor V preparation showed multiple bands, but results are inconclusive with regard to a possible subunit structure for this factor. The purified factor V was stable for at least 1-2 weeks when stored at 4 degrees C in 0.2 M Tris-acetate, 50 mM CaCl2, 10% glycerol, pH 7.5. When stored at -20 degrees C in 50% glycerol, this preparation was stable for several months. Treatment of the purified factor V with bovine factor Xa, RVV-V, thrombin, or chymotrypsin (but not trypsin) led to a seven- to ten-fold increase in clotting activity and a concomitant decrease in apparent molecular weight. The latter was comparable for each activation system yielding the following average molecular weight values: factor VaSa, 246,000-, factor Va RVV-V, 251,500; Factor Vathr, 239,000; alpha-chymotrypsin, but not trypsin, can activate plasma factor V yielding a product similar to that observed with the above activators. The molar quantities of each of the activators required varied considerably with thrombin having the highest specific activity and factor Xa the lowest. Activation by factor Xa was greatly facilitated by the addition of phospholipid. In the presence of a mixture of phosphatidylcholine/phosphatidylserine (1:1, w/w), the activation of factor V by factor Xa plus Ca2+ required one-third the amount of factor Xa protein as that required in the absence of phospholipid. Even though each of these activators appears to act in an enzymatic manner, the chemical nature of the conversion is unknown at this time.
...
PMID:The activation of factor V by factor Xa or alpha-chymotrypsin and comparison with thrombin and RVV-V action. An improved factor V isolation procedure. 126 97

The jawed leech, Hirudinaria manillensis is closely related to Hirudo medicinalis, both belonging to the same family Arhynchobdellida. From Hirudo, two potent peptide inhibitors, hirudin (a thrombin inhibitor) and eglin (an elastase/chymotrypsin inhibitor) have been characterised in detail. During our studies to isolate thrombin inhibitor from the leech Hirudinaria a potent inhibitor, analogous to eglin, was also detected. Results indicate that this inhibitor, which we have named 'GELIN', is significantly different from eglin. Gelin was isolated and purified to homogeneity by ion exchange chromatography and reverse phase HPLC. The isoelectric point of Gelin was estimated to be 4.55, in contrast to 6.45 for eglin. The molecular weight of Gelin was similar to eglin, as estimated by SDS-PAGE. Amino-terminal sequence analysis of the first 29 residues show no sequence homology with eglin or any other serine protease inhibitors. Circular dichroism studies showed that the secondary structure of Gelin has no helix, 58% beta sheets and 42% random structures compared to 19% helix, 56% beta sheets and 25% random structures in eglin. Like eglin, Gelin inhibits elastase, cathepsin G and chymotrypsin but has little or no activity towards plasmin, thrombin, pepsin and trypsin. These data suggest that the elastase inhibitors from these two species of leech are fundamentally different in structure, indicative of independent evolutionary origin.
...
PMID:Biochemical characterisation of a pancreatic elastase inhibitor from the leech Hirudinaria manillensis. 128 66

Thrombin is a multifunctional serine proteinase that plays a key role in coagulation while exhibiting several other key cellular bioregulatory functions. The X-ray crystal structure of human alpha-thrombin was determined in its complex with the specific thrombin inhibitor D-Phe-Pro-Arg chloromethylketone (PPACK) using Patterson search methods and a search model derived from trypsinlike proteinases of known spatial structure (Bode, W., Mayr, I., Baumann, U., Huber, R., Stone, S.R., & Hofsteenge, J., 1989, EMBO J. 8, 3467-3475). The crystallographic refinement of the PPACK-thrombin model has now been completed at an R value of 0.156 (8 to 1.92 A); in particular, the amino- and the carboxy-termini of the thrombin A-chain are now defined and all side-chain atoms localized; only proline 37 was found to be in a cis-peptidyl conformation. The thrombin B-chain exhibits the characteristic polypeptide fold of trypsinlike serine proteinases; 195 residues occupy topologically equivalent positions with residues in bovine trypsin and 190 with those in bovine chymotrypsin with a root-mean-square (r.m.s.) deviation of 0.8 A for their alpha-carbon atoms. Most of the inserted residues constitute novel surface loops. A chymotrypsinogen numbering is suggested for thrombin based on the topological equivalences. The thrombin A-chain is arranged in a boomeranglike shape against the B-chain globule opposite to the active site; it resembles somewhat the propeptide of chymotrypsin(ogen) and is similarly not involved in substrate and inhibitor binding. Thrombin possesses an exceptionally large proportion of charged residues. The negatively and positively charged residues are not distributed uniformly over the whole molecule, but are clustered to form a sandwichlike electrostatic potential; in particular, two extended patches of mainly positively charged residues occur close to the carboxy-terminal B-chain helix (forming the presumed heparin-binding site) and on the surface of loop segment 70-80 (the fibrin[ogen] secondary binding exosite), respectively; the negatively charged residues are more clustered in the ringlike region between both poles, particularly around the active site. Several of the charged residues are involved in salt bridges; most are on the surface, but 10 charged protein groups form completely buried salt bridges and clusters. These electrostatic interactions play a particularly important role in the intrachain stabilization of the A-chain, in the coherence between the A- and the B-chain, and in the surface structure of the fibrin(ogen) secondary binding exosite (loop segment 67-80).(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:The refined 1.9-A X-ray crystal structure of D-Phe-Pro-Arg chloromethylketone-inhibited human alpha-thrombin: structure analysis, overall structure, electrostatic properties, detailed active-site geometry, and structure-function relationships. 130 49


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---