Autocatalytic coagulation

In the extravascular pathway (right), tissue thromboplastin (factor 111), a membrane protein in the deeper layers of the vascular wall, activates coagulation factor Vll. The activated form of this (Vila) autocatalytically promotes its own synthesis and also generates the active factors IXa and Xa from their precursors. With the aid of factor Villa, PL, and Ca factor IXa produces additional Xa, which finally— with the support of Va, PL, and Ca ""—releases active thrombin. 

The rate of coagulation of night blue examined by Biltz and Steiner Zeit, Phys. Ohem, LXXili. 607, 1910) and of benzo-purpurin (Biltz and v, Vegesack, Zeit. Phys. Ghem. lxxiii. 500, 1910) likewise appear to conform reasonably closely to a reaction of the autocatalytic variety. 

Fig. 9.4 The coagulation cascade in the horseshoe crab amoebocyte lysate. In the presence of LPS, the Factor C serine protease zymogen is autocatalytically activated to an active form, Factor C , which activates the proenzyme Factor B into Factor B . This in turn activates proclotting to active clotting enzyme. Clotting enzyme then converts coagulogen into a coagulin gel clot, which traps the invading bacteria...

Chymosin is secreted by the abomasum in the form of an intially inactive precursor, prochymosin, which is converted autocatalytically to chymosin (see below, p. 176). Many reviews on the properties of the zymogen and the enzyme have been published. One of the most recent, by Foltmann (J), also contains references to earlier reviews. The action of chymosin on K-casein is primarily responsible for the milk-clotting process. The numerous studies of this reaction have been reviewed recently by Mackinlay and Wake (32). Because of the number of diflFer-ent milk proteins and the complexity of their interactions, especially in the casein micelle, the full details of the coagulation process are not yet understood. 

NovoSeven is an unusual product in that it is (a recombinant form of) human coagulation factor VII (FVII). The product is converted in an autocatalytic fashion into the active two-chain form (FVIIa) during its chromatographic purification. NovoSe-... 

Examination of the coagulation cascade has shown that it gives rise to an S-shaped curve when the rate of production of thrombin is plotted against its concentration, — the reaction is self-catalyzing or autocatalytic (Figure 9.11). The process is balanced by the rate at which thrombin is swept away from the vessel wall by mass transfer to fhe flowing blood. Because thrombin concentration in the bulk fluid, Q, is nearly constanf and low, we can wrife... 

In accordwce with the theory orthokinetic flocculation presents an autocatalytic character In the beginning when the particles are still smaU the coagulation is peri-kinetic and its rate is slow When a certain degree of aggregation has been reached orthokinetic coagulation comes into play and aggregation is accelerated very much ... 

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