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| http://purl.uniprot.org/citations/15210795 | http://www.w3.org/2000/01/rdf-schema#comment | "Complement factor I (fI) plays a major role in the regulation of the complement system. It circulates in an active form and has very restricted specificity, cleaving only C3b or C4b in the presence of a cofactor such as factor H (fH), complement receptor type 1, membrane cofactor protein, or C4-binding protein. Using peptide-7-amino-4-methylcoumarin derivatives, we investigated the substrate specificity of fI. There is no previous report of synthetic substrate cleavage by fI, but five substrates were found in this study. A survey of 15 substrates and a range of inhibitors showed that fI has specificity similar to that of thrombin, but with much lower catalytic activity than that of thrombin. fI amidolytic activity has a pH optimum of 8.25, typical of serine proteases and is insensitive to ionic strength. This is in contrast to its proteolytic activity within the fI-C3b-fH reaction, in which the pH optimum for C3b cleavage is <5.5 and the reaction rate is highly dependent on ionic strength. The rate of cleavage of tripeptide 7-amino-4-methylcoumarins by fI is unaffected by the presence of fH or C3(NH(3)). The amidolytic activity is inhibited by the synthetic thrombin inhibitor Z-D-Phe-Pro-methoxypropylboroglycinepinanediol ester, consistent with previous reports, and by benzenesulfonyl fluorides such as Pefabloc SC. Suramin inhibits fI directly at concentration of 1 mM. Within a range of metal ions tested, only Cr(2+) and Fe(3+) were found to inhibit both the proteolytic and amidolytic activity of fI."xsd:string |
| http://purl.uniprot.org/citations/15210795 | http://purl.org/dc/terms/identifier | "doi:10.4049/jimmunol.173.1.367"xsd:string |
| http://purl.uniprot.org/citations/15210795 | http://purl.uniprot.org/core/author | "Sim R.B."xsd:string |
| http://purl.uniprot.org/citations/15210795 | http://purl.uniprot.org/core/author | "Tsiftsoglou S.A."xsd:string |
| http://purl.uniprot.org/citations/15210795 | http://purl.uniprot.org/core/date | "2004"xsd:gYear |
| http://purl.uniprot.org/citations/15210795 | http://purl.uniprot.org/core/name | "J Immunol"xsd:string |
| http://purl.uniprot.org/citations/15210795 | http://purl.uniprot.org/core/pages | "367-375"xsd:string |
| http://purl.uniprot.org/citations/15210795 | http://purl.uniprot.org/core/title | "Human complement factor I does not require cofactors for cleavage of synthetic substrates."xsd:string |
| http://purl.uniprot.org/citations/15210795 | http://purl.uniprot.org/core/volume | "173"xsd:string |
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