Participation of a proton-translocating plasma membrane ATPase, acid phosphatase and alkaline phosphatase in ATP degradation by Aspergillus niger extracts.

Extracts of A. niger could catalyze sequential hydrolysis of the three phosphate moieties of the ATP molecule optimally at pH 2 and at pH 8. At pH 2 the hydrolysis was effected by an ATPase followed by acid phosphatase while at pH 8 alkaline phosphatase was the only involved enzyme. Separation of these three phosphate-hydrolyzing enzymes was achieved by Sephadex G-100 column chromatography. The A. niger ATPase seems to have two unique features. First, it was easily solubilized in distilled water and second it had optimum activity at pH 2. The activity of this enzyme was not affected on addition of Na+, K+ or Ca2+ to the assay reaction mixture. It was neither inhibited by sodium azide nor by potassium nitrate but inhibited by orthovanadate, DES, DCCD, Mg2+ and Pi. The substrate concentration-activity relationship was of the hyperbolic type. The enzyme had high specificity for ATP, was inert with ADP and its activity with GTP represented about 6% only of that obtained with equimolar amount of ATP.