Studies on the microsomal sodium-plus-potassium ion-stimulated adenosine triphosphatase system in rat ventral prostate

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Abstract
A Mg2++Na++K+-stimulated adenosine triphosphatase (ATPase) preparation was isolated from rat ventral prostate by flotation of microsomal membranes in high-density sucrose solutions. The reaction medium for optimum Na++K+-stimulated ATPase activity was found to be: Na+, 115mm; K+, 7–10mm; Mg2+, 3mm; ATP, 3mm; tris buffer, pH7·4 at 38°, 20mm. The average ΔPi (Mg2++Na++K+ minus Mg2++Na+) was 9μmoles/mg. of protein/hr., representing a 30% increase over the Mg2++Na+-stimulated ATPase activity. At high concentrations, K+ was inhibitory to the enzyme activity. Half-maximal inhibition of Na++K+-stimulated ATPase activity was elicited by ouabain at 0·1mm. The preparation exhibited phosphatase activity towards ribonucleoside triphosphates other than ATP. However, stimulation of Pi release by Na++K+ was observed only with ATP as substrate. The apparent Km for ATP for Na++K+-stimulated activity was about 0·3×10−3m. Ca2+ inhibited only the Na++K+-stimulated ATPase activity. Mg2+ could be replaced by Ca2+ but then no Na++K+ stimulation of ATPase activity was noticed. The addition of testosterone or dihydrotestosterone (17β-hydroxy-5α-androstan-3-one) in vitro at 0·1–10μm under a variety of experimental conditions did not significantly increase the Na++K+-stimulated ATPase activity. The enzyme preparations from prostates of orchidectomized rats, however, exhibited a drastic decrease in the specific activity of Na++K+-stimulated ATPase; these changes were prevented in the orchidectomized rats by injection of testosterone propionate.