Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.4 (trypsin)
 42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Factor D (C3 proactivator convertase) of human serum has been shown to be absolutely necessary for alternative pathway function, for activation of the C3/C5 convertase of that pathway and not to be a subunit of this enzyme. Factor D was found to be present in human plasma in active form only, at a concentration of 2 microgram/ml, and not to be controlled by plasma protease inhibitors or by spontaneous decay. Unlike trypsin, factor D cleaves and activates factor B only when it is in Mg++-dependent complex with C3b, has no esterolytic activity, and is unable to cleave the B chain of insulin. The alleged functional and antigenic relationship of factor D to alpha-thrombin could not be verified. The results of this study led to the description of the mechanism of action of factor D in terms of the cryptic site hypothesis.
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PMID:Mechanism of action of factor D of the alternative complement pathway. 8 4

An active C3 cleaving enzyme is generated when properdin factor B (glycine-rich beta-glycoprotein, GBG) is activated (GBG is cleaved) by factor D in the presence of C3b and Mg++. Factor D can be replaced by trypsin in this reaction but even then C3b and Mg++ are required. In the absence of C3b and/or Mg++ trypsin does not generate C3 cleaving activity from GBG although it cleaves GBG and releases its GGG fragment (B) under these conditions as well. Addition of C3b to GGG immediately after its release does not yield a C3 cleaving enzyme. These findings indicate that C3b, GBG and Mg++ interact, and that only in association with C3b can GBG be cleaved in a way that its enzyme activity, residing in a C3b, GGG complex, is expressed. The complex is labile (half-life at 20 degrees C: 9 minutes); Mg++ does not affect its stability nor is it essential for the activity. It was possible to sequentially fix on agarose the essential components of the C3 cleaving enzyme and thus to elucidate the single steps and the order of its formation. C3 was activated and the resulting C3b fragment fixed on agarose by incubating C3 with trypsin covalently bound to the agarose. The agarose-C3b intermediate was capable of binding GBG provided Mg++ was present. GBG could then be cleaved by factor D or trypsin added in solution; the solid-phase-fixed complex obtained had C3 cleaving activity, in the presence as well as absence of Mg++. Omission of any of these steps or components, or changes in the sequence did not give rise to an active enzyme. Mixtures of C3b, GBG and Mg++ have weak C3 cleaving activity by themselves. C3 cleavage in such incubation mixtures proceeds slowly for hours and is not accompanied by cleavage of GBG. There is thus complete analogy between the CVF-dependent and C3b-dependent C3 cleaving systems. C3b and CVF act in the same way, they form a reversible, weakly active C3 cleaving complex with GBG and Mg++, the activity of which is markedly enhanced but becomes subject to decay when GBG is cleaved by trypsin-like enzymes while bound to CVF or C3b.
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PMID:Formation and composition of the C3 activating enzyme complex of the properdin system. Sequential assembly of its components on solid-phase trypsin-agarose. 12 76

Complexes formed of Cobra venom factor (CVF) and activated factor B (B) by interaction of CVF and B with trypsin or factor D are capable of activating the third and fifth complement component. When incubated with sheep or guinea pig red cells and guinea pig serum in the presence of EDTA, these CVFB complexes produce "indirect lysis". Addition of a human serum factor, earlier designated as factor E (6), greatly enhances the efficiency of this lytic system. The component with this activity has been purified to homogeneity (disc and immunoelectrophoresis). In chromatographic fractionations it was inseparable from the fifth complement component, it was inactivated by and reacted with several anti-C5 antisera, and kinetics of inactivation by heat (56 degrees C) and trypsin were the same for factor E and hemolytic C5 activities. It is concluded that factor E is the fifth component of human complement. Guinea pig C5 is not capable of supporting indirect lysis in a comparable manner, for as yet unknown reasons. Some possible explanations are discussed.
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PMID:Purification of a human serum protein ("factor E") which enhances cobra venom factor-induced indirect lysis. Identification with the fifth component of complement. 13 30

Fibrinolytic activity of normal plasma and blood has been measured by 125l-fibrin solid phase assay. Activity of plasma is not affected by removal of plasminogenplasmin by affinity chromatography. Activities of euglobulin and pseudoglobulin fractions are approximately equal. epsilon-aminocaproic acid (EACA) (10 mM), tranexamic acid (10 mM), diisopropylfluorophosphate (DFP, 50 mM), and soybean and lima bean trypsin inhibitors (100 mug/ml) do not inhibit plasma activity at concentrations that inhibit pure plasmin and urokinase-activated plasma. Activity is not affected by glass contact and is not inhibited by inhibitors of contact or enzymatic activation of Hageman factor (hexadimethrine bromide, 100 mug/ml; cytochrome C, 250 mug/ml; spermidine, 2 mM; phenylmethylsulfonylfluoride, 1 mM). It is inhibited partially (30%-40%) by heating (56 degrees C, 30 min) and by zymosan (2.5 mg/ml; 40%-90% inhibition), and is increased by hydrazine (20 mM), salicylaldoxime (20 mM), DFP (50 mM), and tosyl-L-arginine methyl ester (TAMe, 10 mM)-the latter two at concentrations known to inhibit Cls of the classic, and factor D of the alternate complement pathways. Increase fibrinolytic activity with TAMe is associated with reciprocal decrease in classic and alternate complement pathway activity. It is concluded that normal plasma fibrinolytic activity is relatively independent of plasmin as the ultimate fibrinolytic enzyme, that Hageman factor-dependent pathways are of minor importance, and that significant heat-stable and heat-labile nonplasmin fibrinolytic activities are operative. These may include proteinases involved in complement activation, and in common control of classic and alternate complement pathways, as well as other nonplasmin proteinases.
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PMID:Fibrinolysis in normal plasma and blood: evidence for significant mechanisms independent of the plasminogen-plasmin system. 13 51

A protein that specifically enhances up to 13-fold the rate of copying of poly(dT) template by DNA polymerase alpha was partially purified from chromatin of regenerating mouse liver cells. This stimulatory protein, designated herein factor D, also increases 2-3-fold the activity of polymerase alpha with heat-denatured DNA and with primed, circular single-stranded phi X174 DNA. However, factor D has no detectable effect on the copying by polymerase alpha of poly(dG), poly(dA), and poly(dC) templates. Activity of mouse DNA polymerase beta is not affected by factor D with all the tested templates. In contrast to polymerase alpha, factor D is resistant to inactivation by N-ethylmaleimide and calcium ions, but it is readily heat-inactivated at 46 degrees C and is inactivated by trypsin digestion. Partially purified factor D is not associated with detectable activities of DNA polymerase, DNA primase, deoxyribonucleotidyl terminal transferase, and endo- or exodeoxyribonuclease.
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PMID:A DNA template recognition protein: partial purification from mouse liver and stimulation of DNA polymerase alpha. 409 24

The activity of properdin factor D was measured by the generation of the hemolytically active cellular intermediate, EAC43B(D), bearing the C3b-dependent alternate pathway C3 convertase. Treatment of factor D with DFP prevented formation of EAC43B(D); thus, a serine esterase is essential for the generation of the alternate pathway C3 convertase, a situation analogous to the role of C1 in the formation of the classical C3 convertase, C42. The definition of factor D as a serine esterase prompted a search for its proenzyme form, and resulted in the chromatographic isolation from plasma of a single peak of trypsin-inducible factor D activity, distinct from activated factor D. Analytical gel filtration indicated an apparent mol wt of 25,000. This protein from which trypsin elaborated factor D activity, as assessed by the formation of EAC43B(D), the generation of the CoVF-dependent C3 convertase, and the cleavage of factor B in the presence of C3b, was designated "precursor factor D." The DFP resistance of precursor factor D, and the susceptibility of its trypsin-activated form to inactivation by DFP is analogous to the behavior of other plasma serine esterases, including C1.
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PMID:Properdin factor D: characterization of its active site and isolation of the precursor form. 485 53

The amino acid sequence of human factor D is proposed from the analysis of the peptides produced by treatment of the factor D with cyanogen bromide, iodosobenzoic acid, trypsin and V-8 protease. Comparison of the proposed sequence with the sequences of other serine esterases indicated that factor D, although it is a plasma serine esterase, is more closely related to certain proteases not found in the plasma than to other plasma serine esterases of the complement system. For example, 36% and 32% identity in amino acid sequence was found on comparison of factor D with elastase and group-specific protease, respectively. Whereas only 27% and 18% identity was observed between factor D and the other complement serine esterases, Clr and factor B, respectively.
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PMID:Amino acid sequence of human factor D of the complement system. Similarity in sequence between factor D and proteases of non-plasma origin. 636 33

An adult twin with recurrent bacterial infections was found to have a partial functional deficiency of complement factor D. Full restoration of alternative pathway activity and zymosan- or cobra venom factor-induced consumption of C3 and B was found after reconstitution of patient's serum with purified D. Family studies revealed normal D levels in the mother, a brother and another sister. After gel filtration of patient's sera only little D activity could be detected in the fractions, and trypsin activation of the fractions also did not uncover detectable precursor D activity.
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PMID:Functional deficiency of complement factor D in a monozygous twin. 656 50

Hexapeptides mimicking the partial amino acid sequence of factor B surrounding the bond that is cleaved by factor D have been synthesized. These peptides have been assessed for their ability to inhibit factor D enzymatic activity and for their susceptibility to serine proteases. The synthetic peptides were cleaved by bovine trypsin and C1s but not by alpha-thrombin and factor D. The peptides inhibited factor B cleavage and fluid-phase or cell-bound alternative pathway C3 convertase activation by factor D. Altogether, these results suggest that peptides analogous to factor B specifically inhibit factor D enzymatic activity. Thus, they constitute an interesting tool for study of alternative pathway activation and can be of use when attempting to manipulate this pathway, since factor D is an essential component for alternative pathway initiation and amplification.
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PMID:Inhibition of alternative pathway factor D by factor B-related synthetic hexapeptides. 692 Feb 99

Human factor D purified to homogeneity by a modified procedure was subjected to NH2-terminal amino acid sequence analysis by using a modified automated Beckman sequencer. We identified 48 of the first 57 NH2-terminal amino acids in a single sequencer run, using microgram quantities of factor D. The deduced amino acid sequence represents approximately 25% of the primary structure of factor D. This extended NH2-terminal amino acid sequence of factor D was compared to that of other trypsin-related serine proteases. By visual inspection, strong homologies (33--50% identity) were observed with all the serine proteases included in the comparison. Interestingly, factor D showed a higher degree of homology to serine proteases of pancreatic origin than to those of serum origin.
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PMID:Partial amino acid sequence of human factor D:homology with serine proteases. 698 65


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