Protein phosphokinase activity endogenous to rat ventral prostate chromatin was assayed by using dephosphophosvitin as an exogenous substrate. For maximal activity of the kinase reaction, the presence of 200 mM NaCl, 5 mM MgCl2, and 1 mM dithiothreitol was essential. Two apparent pH optima were observed, a broad one between pH 7 and 7.4, and one at pH 7.89. At pH 7.4 the apparent K(m) for 31% dephosphophosvitin was 0.3 mg per ml. With respect to ATP, 2 apparent K(m) values (0.04 and 0.41 mM) were found. The kinase activity was minimal toward exogenous histones when used as substrates (3% for lysine rich and 0.3% for arginine rich (f3) histones, compared with dephosphophosvitin controls). The protein phosphokinases were not significantly stimulated by cyclic adenosine 3':5' monophosphate (cyclic AMP) when histones were used as substrate. With dephosphophosvitin as substrate, cyclic AMP produced a small inhibition (5 to 15%). Orchiectomy of adult rats resulted in a rapid decline in the chromatin associated protein phosphokinase activity assayed using optimal experimental conditions described above. At 9 hr postorchiectomy, a 30% decline in the activity was observed; this was further reduced to about 50% of the control by 18 hr. This decrease in the kinase activity (e.g. at 9 hr postorchiectomy) appears to precede measurable changes in the protein and RNA complements of chromatin. Testosterone replacement following orchiectomy abolished this decline in the chromatin associated activity. The chromatin associated protein phosphokinase activity toward lysine rich and arginine rich histones was also sensitive to androgenic status of the animals and declined rapidly postorchiectomy. The results suggest the presence of multiple and androgen sensitive protein phosphokinases associated with rat ventral prostate chromatin, which may modulate the phosphorylation of nuclear nonhistone phosphoproteins.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|State||Published - 1975|