Regulatory system of guinea-pig complement C3b: two factor I-cofactor proteins on guinea-pig peritoneal granulocytes.
Complement factor I is a plasma protease serving for proteolytic inactivation of C3b together with its cofactor. We have identified two factor I-cofactor activities in solubilized extracts of guinea-pig peritoneal granulocytes using guinea-pig factor I (Igp) and fluorescent-labeled methylamine-treated guinea-pig C3 (f-C3(MA)gp). One of these eluted from a chromatofocusing column between pH 7.6-7.1, and the other at about pH 5.7. These two cofactor fractions both interacted with Igp and, to a lesser degree, with human factor I (Ihu) on C3(MA)gp cleaving it into an inactive C3bi analogue, but did not cleave methylamine-treated human C3 (C3(MA)hu) together with Igp or Ihu. These factors are therefore species specific. The neutral and acidic fractions with cofactor activity contained C3(MA)gp-binding proteins with a doublet of 55 kDa and 42 kDa, and a singlet of 160 kDa, respectively, on SDS-PAGE. These proteins may be membrane cofactor protein (MCP) and C3b/C4b receptor (CR1) of guinea-pigs.
Seya
T
T
Department of Immunology, Center for Adult Diseases, Osaka, Japan.
Okada
M
M
Hazeki
K
K
Nagasawa
S
S
D000818:Animals; D001202:Ascitic Fluid / Q000166:cytology; D002845:Chromatography; D003167:Complement Activation; D003179:Complement C3b; D017244:Complement Factor I; D005456:Fluorescent Dyes; D006098:Granulocytes / Q000378:metabolism*; D006168:Guinea Pigs; D006801:Humans; D008744:Methylamines; D012697:Serine Endopeptidases / Q000378:metabolism*; D013329:Structure-Activity Relationship
D005456:Fluorescent Dyes; D008744:Methylamines; D003179:Complement C3b; C027451:methylamine; D012697:Serine Endopeptidases; D017244:Complement Factor I