Comparison of structures of various human fibrinogens and a derivative thereof by a study of the kinetics of release of fibrinopeptides

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Abstract
The kinetics of the thrombin-induced release of fibrinopeptides from several variants of human fibrinogen, and from the plasmin digestion fragment E thereof, were studied by using an HPLC [high performance liquid chromatography] technique to separate the reaction products. The data were analyzed in terms of a Michaelis-Menten mechanism in which the A.alpha. and B.beta. chains compete for thrombin. Phosphorylation of Ser-3 of the A.alpha. chain appears to increase the rate of release of the corresponding phosphorylated peptide A from fibrinogen, due to enhanced binding of thrombin (lower value of the Km). However, phosphorylation does not affect the rate of release of the unphosphorylated A or B peptides. Increase in the length of the .gamma. chain (at the C-terminus) does not affect the rate of release of any of the fibrinopeptides. The rate of release of the A peptide from fragment E (which is devoid of the B peptide) is similar to that for the the complete fibrinogen molecule. These results are in agreement with an earlier conclusion that the A.alpha. and B.beta. chains behave independently in their competition for thrombin; i.e., the hydrolyzable Arg-Gly bonds of the A.alpha. and B.beta. chains are both accessible to thrombin.
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