Abstract
Protein kinase in human seminal plasma, as assayed by its ability to catalyze the transfer of phosphate from [.gamma.-32P]ATP to protamine, linearly increased with dilution of the seminal plasma. Extrapolation of the enzyme activity to the undiluted seminal plasma indicated that protein kinase existed in the ejaculate as the inactive enzyme. An inhibitor of the protein kinase was postulated and the results suggested that the inhibitor was a heat-labile macromolecule. The linear increase of the protein kinase activity could also be obtained by increasing ATP concentration. In addition, a high Mg2+-dependent ATPase activity was found in the seminal plasma; its activity exhibited an inverse relationship with the activity of the protein kinase. The apparent inhibitor of protein kinase in the human seminal plasma was the destruction of ATP by the ATPase.

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