| properdin | <protein> Component of the alternative pathway for complement activation: complexes with C3b and stabilises the alternative pathway C3 convertase (C3bBbP) that cleaves C3. (18 Nov 1997) |
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| properdin factor A | A component of the properdin system; a hydrazine-sensitive b1-globulin (mw about 180,000), now known to be C3 (third component of complement). (05 Mar 2000) |
| properdin factor b | <enzyme> A glycine-rich, heat-labile beta-glycoprotein found in blood. It is a proactivator of complement 3 in the alternate pathway of complement activation. Factor b is converted by factor d to c3 convertase. Registry number: EC 3.4.21.47 (12 Dec 1998) |
| properdin factor d | <enzyme> A serum protein which during the alternate pathway of complement activation converts the inactive properdin factor b to c3 convertase. Registry number: EC 3.4.21.46 (12 Dec 1998) |
| properdin factor E | A serum protein (mw 160,000) required for activation of C3 (third component of complement) by cobra venom factor. See: properdin system. (05 Mar 2000) |
| properdin system | An immunological system that is the alternative pathway for complement, composed of several distinct proteins that react in a serial manner and activate C3 (third component of complement), seemingly without utilizing components C1, C4, and C2; in addition to properdin, the system includes properdin factors A (native C3), B (C3 proactivator), D (C3 proactivator convertase), and perhaps at least one other, E; the system can be activated, in the absence of specific antibody, by bacterial endotoxins, by a variety of polysaccharides and lipopolysaccharides, and by a component of cobra venom. (05 Mar 2000) |