摘要：

A chromatographic procedure has been developed for the separation and purification of bovine α- and β-thrombin. α-Thrombin has a specific activity of 2400–3000 NIH U/mg while β-thrombin has only approximately 100 NIH U/mg. When assayed with an ester substrate, the two forms have equivalent activity while β-thrombin has only 30% of the activity of α-thrombin toward an anilide substrate. Previous studies have suggested that the degradation of α-thrombin produces a species in which a peptide fragment containing a disulfide bridge is lost. The amino acid composition determined in the present study indicates that the content of cysteine is identical in the two forms of the enzyme thus permitting the proposal of a structure for β-thrombin which differs from that currently in the literature. It is suggested that changes in the environment of the active site histidine residue in the two species is largely responsible for the observed changes in the catalytic activity.

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