Calcium effects on prothrombin and its reaction with bifunctional alkylating reagents

Monodisperse bovine prothrombin was prepared and its molecular states under several conditions examined. The protein showed no tendency to self-associate in the absence of calcium. Calcium (4 mM) caused small increases in the apparent molecular weight of the protein which may or may not represent protein dimerization with very low affinity. The allowed conclusion was that calcium-induced prothrombin dimerization is minimal up to protein concentrations of many mg/ml. Calcium-induced protein shape changes did not measurably alter the protein diffusion constant. A bifunctional alkylating reagent did produce extensive calcium-dependent prothrombin crosslinking. Prothrombin dimers formed by the crosslinking agent were not a measure of the state of native prothrombin.