title: Inhibition and complexation of activated protein C by two major inhibitors in plasma.
abstract: To determine the major physiologic inhibitors of activated protein C (APC), plasma was incubated with APC or with Protac C and subjected to immunoblotting. APC:inhibitor complexes gave two major bands reacting with antiprotein C antibodies when immunoblotted on nondenaturing gels, and additional minor bands that varied between serum and plasma. Formation of one of the two major bands of APC:inhibitor complex, but not the other, was stimulated by heparin and only this band reacted with antibodies to the previously described APC inhibitor that is here designated PCI-1. Plasma immunodepleted of PCI-1 formed complexes with APC as visualized with antiprotein C but not anti-PCI-1 antibodies, and exhibited heparin-independent inhibition of APC activity, providing evidence for the existence of a second major physiologic APC inhibitor, PCI-2. Formation of APC:PCI-2 complexes in PCI-1-depleted plasma paralleled inhibition of APC amidolytic activity. PCI-2 was separated from PCI-1 and partially purified using column chromatography. PCI-2 formed inactive complexes of approximately 110,000 molecular weight (mol wt) with APC suggesting PCI-2 has an approximate mol wt of 50,000. Thus, inhibition of APC in plasma involves two major distinct 50,000 mol wt inhibitors, the heparin-dependent PCI-1 and the heparin-independent PCI-2.
authors.affiliation: Department of Immunology, Research Institute of Scripps Clinic, La Jolla, CA 92037.
authors.forename: M J
authors.initials: MJ
authors.lastname: Heeb
authors.forename: F
authors.initials: F
authors.lastname: España
authors.forename: J H
authors.initials: JH
authors.lastname: Griffin
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D000937:Antigen-Antibody Reactions; D004789:Enzyme Activation; D006801:Humans; D015151:Immunoblotting; D008297:Male; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000097:blood* / Q000302:isolation & purification; D011480:Protease Inhibitors / Q000097:blood* / Q000502:physiology; D011486:Protein C / Q000037:antagonists & inhibitors* / Q000097:blood / Q000276:immunology; D011817:Rabbits
chemical_list: D000911:Antibodies, Monoclonal; D009097:Multienzyme Complexes; D011480:Protease Inhibitors; D011486:Protein C