Role of calcium ion in the generation of factor XIII activity

The involvement of calcium ion in the activation of both plasma factor XIII (alpha 2 beta 2) and platelet factor XIII (alpha 2) was investigated. The second-order dependence of the rate constant for exposure of the active-site thiol group of alpha-thrombin-cleaved plasma factor XIII (alpha 2'be...

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Bibliographic Details
Published in:Biochemistry (Easton) 1991-06, Vol.30 (25), p.6175-6182
Main Authors: Hornyak, Thomas J, Shafer, Jules A
Format: Article
Language:English
Subjects:
Allosteric Regulation
Binding Sites
Biological and medical sciences
Blood Coagulation
Blood coagulation. Blood cells
Calcium - blood
coagulation factor XIII
Coagulation factors
Factor XIII - metabolism
Fundamental and applied biological sciences. Psychology
Humans
Iodoacetamide - metabolism
Kinetics
Models, Molecular
Molecular and cellular biology
Platelet Activation
Sulfhydryl Compounds - blood
Thrombin - metabolism
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Summary:The involvement of calcium ion in the activation of both plasma factor XIII (alpha 2 beta 2) and platelet factor XIII (alpha 2) was investigated. The second-order dependence of the rate constant for exposure of the active-site thiol group of alpha-thrombin-cleaved plasma factor XIII (alpha 2'beta 2) on the concentration of calcium ion suggested that the binding of two calcium ions is required for transformation of the alpha 2'beta 2 tetramer to enzymatically active factor XIIIa. Fibrinogen, previously reported to lower the calcium ion concentration required for efficient activation of alpha 2'beta 2 [Credo, R. B., Curtis, C. G., & Lorand, L. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 4234-4237], was found in the present study to increase the rate of exposure of the active-site thiol group. Whereas calcium ion is required for exposure of the active-site thiol group in cleaved plasma factor XIII (alpha 2'beta 2), exposure of an active-site thiol group in cleaved platelet factor XIII (alpha 2') occurs in the absence of calcium ion. The rate constant (2.2 x 10(5) M-1 s-1) for alpha-thrombin-catalyed exposure of the active-site thiol group of platelet factor XIII zymogen (alpha 2) in the presence of calcium ion was greater than the rate constant (0.7 x 10(5) M-1 s-1) determined in the absence of calcium ion.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi00239a014