Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.1 (chymotrypsin)
 10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The formation of EAC 4b2a is a two step reaction: first, the temperature- and time-independent binding of C2 to EAC4b2a resulting in EAC4b2 , secondly, the enzymatically triggered conversion of EAC4b2 to EAC4b2a . In the classical cascade of complement activation, the generation of C3 convertase activity is triggered by the C1 esterase, C1-s, which is part of C-1. Evidence is presented that the enzymes trypsin, chymotrypsin, plasmin, and pronase are also able to activate EAC4b2 to EAC4b2a . Kinetic studies showed that the formation of C3 convertase by these enzymes was dependent on concentration, temperature, and time. The optimal conditions were found as follows: trypsin, 2 micrograms/ml (final conc.) for 8 min at 23 degrees C; chymotrypsin 165 micrograms/ml for 18 min at 23 degrees C; plasmin 0.8 units/ml for 15 min at 23 degrees C; pronase 1.25 microgram/ml for 15 min at 23 degrees C. Even under optimal (tmax) conditions the number of generated EAC4b2a differed from enzyme to enzyme: trypsin (= 100%), pronase (58.3%), chymotrypsin (47.9%), and plasmin (12.9%). The enzymes were also able to generate C3 convertase activity from C2 which was adsorbed to EAC1i4b , a C1 inactivator treated and therefore hemolytically inactive intermediate ( EAC1i4b2 ). These findings underline the biological importance of C1 esterase replacing enzymes.
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PMID:Generation of the classical pathway C3 convertase (EAC4b2a) by proteolytic enzymes. 637 57

The primary structure of human D, the serine protease activating the C3 convertase of the alternative complement pathway, has been deduced by sequencing peptides derived from various chemical (CNBr and o-iodosobenzoic acid) and enzymatic (trypsin, lysine protease, Staphylococcus aureus V8 protease, and chymotrypsin) cleavages. Carboxypeptidase A was also used to confirm the COOH-terminal sequence. The peptides were purified by high-pressure liquid chromatography. The proposed sequence of human D contains 222 amino acids and has a calculated molecular weight of 23 748. It exhibits a high degree of homology with other serine proteases, especially around the NH2-terminus as well as the three residues corresponding to the active-site His-57, Asp-102, and Ser-195 (chymotrypsinogen numbering). This sequence homology is highest (40%) with plasmin, intermediate (35%) with pancreatic serine proteases, such as elastase, trypsin, chymotrypsin, and kallikrein, and least (30%) with the serum enzymes thrombin and factor X. D, however, exhibits only minimal amino acid homology with the other sequenced complement serine proteases, Clr (25%) and Bb (20%). The substitution of a basic lysine for a neutral amino acid three residues NH2-terminal to the active-site serine as well as a small serine residue for a bulky aromatic amino acid at position 215 (chymotrypsinogen numbering) in the binding pocket may be important in determining the exquisite substrate specificity of D. The presence of His-40 which interacts with Asp-194 (chymotrypsinogen numbering) to stabilize other serine protease zymogens [Freer, S. T., Kraut, J., Robertus, J. D., Wright, H. T., & Xuong, N. H. (1970) Biochemistry 9, 1997] argues in favor of such a D precursor molecule.
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PMID:Amino acid sequence of human D of the alternative complement pathway. 638 66

The entire amino acid sequence of complement factor B has been established combining both protein and DNA sequencing strategies. The zymogen consists of 739 amino acids, has four asparagine-linked carbohydrate sites, and has independently disulfide-bonded NH2- and COOH-terminal regions. The catalytic subunit, Bb, is a unique serine protease containing 259 amino acids that are not integral to any of the classical serine proteases. It is proposed that this region of the Bb fragment functions as a cofactor-binding domain for C3b. The Ba fragment was found to contain three regions of internal sequence homology which were unrelated to the "kringle" regions of prothrombin and plasminogen and which suggest an independent evolution for the B genome. Sequence alignment of the active site of B to the serine proteases was made using the three-dimensional structures of chymotrypsin and trypsin as molecular models. Three stretches within the hypothetical model for B contrast markedly with all known serine proteases in both amino acid sequences and predicted configuration. It is suggested that these "altered" regions contribute at least in part to the formation of the catalytic region of the C3 convertase.
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PMID:Complete primary structure for the zymogen of human complement factor B. 654 54

Human C4b-binding protein (C4BP), which is a regulator of the classical complement pathway C3 convertase, forms high affinity complexes with anticoagulant protein S and with the pentraxin serum amyloid P component (SAP). SAP is a plasma protein present in all amyloid deposits. Recently, SAP was shown to inhibit the complement regulatory functions of C4BP. In this investigation, we have studied the structural requirements for the C4BP-SAP interaction. C4BP was subjected to chymotrypsin digestion, which yielded two major fragments corresponding to the central core (160 kDa) and to the cleaved-off tentacles (48 kDa). SAP-Sepharose specifically bound the 160-kDa fragment, suggesting that the central core of C4BP contains the binding site for SAP. In a quantitative affinity chromatography assay, the dissociation constants for binding of intact C4BP and of the 160-kDa central core fragment to SAP were found to be 30 and 70 nM, respectively. Recombinant C4BP composed of only alpha-chains bound SAP with similar affinity (Kd = 22 nM), whereas nonglycosylated recombinant alpha-chain C4BP (synthesized in the presence of tunicamycin) bound SAP with lower affinity (Kd = 126 nM). This suggests that the carbohydrate moiety of the central core of C4BP is important for binding of C4BP to SAP in contrast to the C4BP beta-chain, which is not required. EDTA, heparin, and phosphorylethanolamine as well as a peptide comprising amino acids 27-39 of SAP were found to completely displace C4BP from the SAP matrix. Moreover, the immobilized SAP peptide bound C4BP in a reaction that, in contrast to the C4BP-SAP interaction, was not dependent on calcium.
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PMID:Serum amyloid P component binding to C4b-binding protein. 759 41

Previous studies have shown that the domestic mites Dennatophagoides pteronyssinus and D. farinae contain allergens with serine protease activity. These proteolytic allergens include trypsin, chymotrypsin, elastase, kallikrein, and C3/C5 convertase. However, it is not known whether the domestic mite Blomia tropicalis shares with other mite species the serine protease activities. The enzymatic activity present in extracts obtained from food-free B. tropicalis was investigated using specific substrates and inhibitors. Based upon the concentration response and inhibition profiles, and the digestion of specific substrates our data demonstrate that extracts from B. tropicalis exhibit several serine-protease-like activities. The enzyme activities detected in the B. tropicalis extracts are trypsin, elastase, chymotrypsin, kallikrein, C3/C5 convertase, and mast cell protease. Our results also demonstrate that kallikrein and C3/C5 convertase-like activities were not significantly affected by the alpha1-antiprotease, a naturally occurring serine protease inhibitor which protects lung mucosa from the enzymatic action. These data strongly suggest that the Echymyopodidae mite B. tropicalis shares at least five serine proteases with members of other mite families, the Glycyphagidae and Pyroglyphidae. In addition, our data demonstrate the potential use of biochemical methods to detect serine proteases for evaluation of mite growth in viitro, or to detect environmental exposures to these enzymes.
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PMID:Detection of serine proteases in extracts of the domestic mite Blomia tropicalis. 1247 79

The C1s protease of the classical complement pathway propagates the initial activation of this pathway of the system by cleaving and thereby activating the C4 and C2 complement components. This facilitates the formation of the classical pathway C3 convertase (C4bC2a). C1s has a Lys residue located at position 628 (192 in chymotrypsin numbering) of the SP domain that has the potential to partially occlude the S2-S2' positions of the active site. The 192 residue of serine proteases generally plays an important role in interactions with substrates. We therefore investigated the role of Lys628 (192) in interactions with C4 by altering the Lys residue to either a Gln (found in many other serine proteases) or an Ala residue. The mutant enzymes had altered specificity profiles for a combinatorial peptide substrate library, suggesting that this residue does influence the active site specificity of the protease. Generally, the K628Q mutant had greater activity than wild type enzyme against peptide substrates, while the K628A residue had lowered activity, although this was not always the case. Against peptide substrates containing physiological substrate sequences, the K628Q mutant once again had generally higher activity, but the activity of the wild type and mutant enzymes against a C4 P4-P4' substrate were similar. Interestingly, alteration of the K628 residue in C1s had a marked effect on the cleavage of C4, reducing cleavage efficiency for both mutants about fivefold. This indicates that this residue plays a different role in cleaving protein versus peptide substrates and that the Lys residue found in the wild type enzyme plays an important role in interacting with the C4 substrate. Understanding the basis of the interaction between C1s and its physiological substrates is likely to lead to insights that can be used to design efficient inhibitors of the enzyme for use in treating diseases caused by inflammation as result of over-activity of the classical complement pathway.
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PMID:The role of the lys628 (192) residue of the complement protease, c1s, in interacting with Peptide and protein substrates. 2527 39