Characterization of Intermediate-Molecular-Weight Acid Phosphatase from Bovine Kidney Cortex

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Abstract
The distribution of acid phosphatases of intermediate molecular weight was determined in various mammalian tissues. The intermediate-molecular-weight acid phosphatases (designated P-II-1 and 2) comprised about 25%of the p-nitrophenyl phosphatase activity in the supernatant of bovine kidney cortex homogenate. The P-II-1 and 2 purified 2, 000 fold showed the pI values of 5.9 and 5.7, respectively, on isoelectric focusing. Apparent molecular weights of both P-II-1 and 2 were estimated to be 42, 000 by Sephadex G-100 gel filtration and 44, 000 by SDS-polyacrylamide disc gel electrophoresis. Both the enzymes catalyzed the hydrolysis of a wide variety of natural phosphomonoesters, except for the phosphoproteins phosphoserine and o-phosphocholine. The enzymes showed a high activity on pyridoxal phosphate, β-glycerophosphate, and 2′-AMP. The optimum activity pH was near 5 with p-itrophenyl phosphate, but was shifted to the neutral range when pyridoxal phosphate was the substrate. The cations Hg2+and Ag+had a marked inhibitory effect. Neither enzyme was inhibited significantly by L-(+)-tartrate or pCMB. The two other types of acid phosphatases, the high-molecular-weight (designated P-I) and low-molecular-weight (designated P-III, were also purified to homogeneity from bovine kidney cortex, and were compared with P-II from several aspects including substrate specificity and susceptibility to various compounds.