Thrombin Formation in Purified Systems

Abstract

SummaryStudy of the kinetic behavior of purified human clotting factors suggests that formation of prothrombin activator from platelets, plasma thromboplastin component (PTC), antihemophilic factor (AHF), Factor V and calcium proceeds by a sequence of reactions. The earliest detectable reaction is slow and involves platelets, PTC and calcium; an intermediate activated PTC is obtained which is free of platelet contamination and is characterized by its kinetic behavior. Platelets are also requisite at a later step in the sequence, possibly in an intermediate formed between activated PTC, AHF, platelets and calcium. Variations in platelets, AHF and PTC result in characteristic responses in the kinetics of thrombin formation.

Thromboplastin Formation

“…Fisch & Duckert (50), in 1959, concluded from the formation rate and yield of Product I in various mixtures, that Factors VIII and IX behave as substrates, and Factor X as an enzyme. The report of Surgenor et al (41) in the same year did not deal with Factor X, a new entity at that time, but it concluded that analy sis of the reactions leading to thrombin formation identified AHG as a sub strate, but Factor IX as behaving "in a distinctly different way." Biggs & Macfarlane [(2) p. 82] had doubts about Fisch & Duckert's selection of a substrate role for Factor IX; they pointed out that this factor is not con sumed during the coagulation process and so it is hard to view it as a sub strate.…”