Characterization of a protein kinase from human seminal plasma

Tissue sources of protein kinase activities in human seminal fluid: studies of normal, oligozoospermic, and vasectomized men

Protein kinase activities in seminal fluids of normo-, hypo-, and oligozoospermic and vasectomized men were measured using lysine-rich histones and partially dephosphorylated phosvitin as acceptor substrates. There was a significant relationship of histone kinase but not phosvitin kinase activities with the number of spermatozoa originally present in the semen. Histone kinase and phosvitin kinase activities were diminished 88% and 62%, respectively, in vasectomy seminal fluid. The sex accessory gland sources of seminal fluid protein kinase activities not associated with spermatozoa were examined in split ejaculates of vasectomized men. Histone kinase activity was greater in the first fractions, suggesting that the prostate is its predominant contributor; whereas the distribution of phosvitin kinase activity did not indicate any preferential accessory gland source of this enzyme.

In vitro specific phosphorylation of the human seminal proteins

A condition for active phosphorylation of the human seminal proteins was achieved by addition of 0% triton X-100 which inhibited the active ATPase. Analysis of the phosphorylated products by SDS-PAGE revealed that the products at 3 min after ejaculation were consisted mainly of the 72K, 70K, and 50K which changed to 25K, 18K and 17.5K at 30 min. There was massive degradation of the seminal plasma proteins during the first 30 min after the ejaculation, resulting in a generation of smaller molecular weight proteins. Comparison of the protein staining pattern and the autoradiographic pattern suggested that the phosphorylation was protein specific and preferentially occurred on larger molecular weight proteins which were subsequently broken down to those of smaller molecular weight. The protein specific phosphorylation was further demonstrated by the result from a two dimensional gel electrophoresis. The specific phosphorylation suggests that side-chain modification of the seminal proteins may regulate a physiological function of the semen.

Presence and characterization of two protein kinase activities in human seminal fluid

The presence of two protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) 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 presence 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 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 catalytic subunit of a cyclic AMP-dependent enzyme. The protein kinase activities of seminal fluids from vasectomized men were 12-20% of those found for seminal fluids of normal men. This suggests that sperm may be a major source of protein kinase activities in seminal fluid.

A simple method to measure the liquefaction rate of human semen

The centrifugation method has been developed to measure the rate of liquefaction in normal human semen. This method is very simple, reliable and convenient. Evidence is presented here to show that the liquefaction rate at ice-bath temperature is much slower than the rate at room temperature.

The apparent inhibitor of the protein kinase in the human seminal plasma: an explanation

The protein kinase in the human seminal plasma, as assayed by its ability to catalyze the transfer of phosphate from [gama-32P]ATP to the protamine, was found to linearly increase with dilution of the seminal plasma. Extrapolation of the enzyme activity to the undiluted seminal plasma indicated that te 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. However, the linear increase of the protein kinase activity could also be obtained by increasing ATP concentration. In addition, a high Mg+2-dependent ATPase activity was found in the seminal plasma, its activity exhibited inverse relationship with the activity of the protein kinase. The results suggested that the apparent inhibitor of the protein kinase in the human seminal plasma was the destruction of ATP by the ATPase.

Enzymic characteristics of an ecto-cyclic AMP-dependent protein kinase in rat epididymal spermatozoa

Intact spermatozoa from rat cauda epididymides possess an ecto-(cyclic AMP-dependent protein kinase) activity that causes the transfer of the terminal phosphate group of ATP to the serine residues of all the histone fractions. The enzyme showed a high degree of substrate specificity for the phosphorylation of histones rather than protamine, casein and phosvitin. The cell-external-surface protein kinase requires Mg2+ for activity, and other bivalent cations such as Mn2+ and Co2+ can substitute partially for Mg2+, whereas Ca2+ and Zn2+ are potent inhibitors of the enzyme. The enzyme has markedly higher affinity for cyclic AMP than for other cyclic nucleotides for its activation, with an apparent Km value for cyclic AmP of 80 nM. Spermatozoal ecto-kinase activity is not due to contamination of broken cells or any possible cell damage during incubation and isolation of spermatozoa. There was no loss of kinase activity from the cells when washed with 2 mM-EDTA, and the histones phosphorylated by intact spermatozoa were located outside the cells. Protein kinase activity of intact cells was strongly inhibited (approx. 90%) by p-chloromercuribenzenesulphonic acid (10 microM), which is believed not to enter the cells. These data provide further support for the localization of a protein kinase on the external surface of spermatozoa.

Prostatic origin of pyruvate kinase activity in human seminal plasma

Pyruvate kinase activity is found in normozoospermic, oligozoospermic, azoospermic and vasectomised human seminal plasma. The split ejaculate technique was used to determine the origin of this enzyme. Sperm number, acid phosphatase activity and fructose concentrations were the control parameters to ensure proper collection. Evidence is presented that the prostate is the major source of pyruvate kinase in human seminal plasma.