The presence of two protein kinase (ATP:protein phosphotransferase, EC 188.8.131.52) activities has been demonstrated in human seminal fluid, utilizing partially dephosphorylated phosvitin and lysine-rich histones as model acceptor substrates. Both kinase activities were maximal in the presenee of MgCl2 and a sulfhydryl-protecting agent such as dithiothreitol; however, the histone kinase was stimulated to a greater extent by the latter. The histone kinase displayed a broad shoulder of activity at pH values of 7.1 to 7.6 with optimal activity at pH 8.0, and was inhibited by increased ionic strength (53% at 160 mM NaCl) and by the cyclic AMP-dependent protein kinase inhibitor from rabbit muscle. The kinase activity towards phosvitin exhibited a broad pH profile with maximal activity at pH 7.2, was slightly stimulated by NaCl (20% at 160 mM), and was unaffected by the cyclic AMP-dependent protein kinase inhibitor. Kinetic studies revealed more than one apparent Km for the protein substrates and ATP. These differences in enzymic properties of kinase activities towards phosvitin and lysine-rich histones strongly indicate the presence of multiple enzymes. It appears that the histone kinase activity is attributable to the free catalyfic subunit of a cyclic AMP-dependent enzyme. The protein kinase activities of seminal fluids from vasectomized men were 12-20% of those round for seminal fluids of normal men. This suggests that sperm may be a major source of protein kinase activities in seminal fluid.
|Original language||English (US)|
|Number of pages||7|
|Journal||Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular|
|State||Published - Jan 18 1982|
Bibliographical noteFunding Information:
We gratefully acknowledge the discussion and critical evaluation of Dr. Khalil Ahmed in the preparation of this manuscript, as well as the excellent technical assistance of Mr. Roger Salem. This work was supported in part by the General Medical Research Funds of the Veterans Administration and the Minnesota Medical Foundation Grant CRF-48-81.
- (Human semen)
- Protein kinase