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BLOOD COAGULATION FACTORS AT PHOSPHOLIPID SURFACES
Author(s) -
Hemker H. C.,
Lindhout M. J.,
Vermeer C.
Publication year - 1977
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.1977.tb41758.x
Subject(s) - citation , library science , medicine , computer science
Two features characterize this scheme: 1. The cascade sequence: the product of one reaction is (part of) the enzyme in the next.3$ * 2 . The complex enzymes. Both the factor X-activating enzyme (“tenase”) and the thrombin-forming enzyme (“prothrombinase”) consist of two proteins (clotting factors) adsorbed to a phospholipid. The activated forms of factor IX and factor X are serine proteases.5--X As such, they have hardly any tenase or prothrombinase To obtain this activity two other components are necessary: another protein (factor VIII or factor V, respectively) and a phospholipid, or rather, a micelle composed of a mixture of phospholipids. The prevailing model of prothrombinase is the following: at the surface of a phospholipid micelle, factor X, and factor V adsorb next to each other. At the same interphase the substrate, prothrombin, adsorbs. The active site in factor X:, attacks the vulnerable sites in prothrombin and so generates thrombin. The evidence leading to this model is the following: 1) The proteins can be shown to adsorb onto the micelles. Activity generates when both adsorb onto the same micelle. Ca+’ is necessary for the adsorption of factor X, but counteracts the adsorption of factor V. Optimal activity is found when about equimolar quantities of both factor adsorb.lO~ ll. 14-~0 The dependence of the activity on the concentrations of the constituent moieties is in accordance with the following reaction scheme: 21, 2 2 X, + Cat+ + ph.lip s Xi, Ca ph.lip. V + ph.lip. $ V ph.lip. V + X, Ca ph.lip. $ prothrombinase X, + Ca+t + V ph.lip. e prothrombinase