Separation and Properties of Three Acid Phosphatases from Human Placenta

Abstract 1. Three chromatographically and enzymatically distinct forms of acid phosphatase have been separated from extracts of human placental villus tissue by gel filtration. 2. These enzymes, termed I, II, and III, have molecular weights of g200,000, 105,000, and 35,000, respectively; and pH optima for p-nitrophenyl phosphate hydrolysis of 5.5, 4, and 5.5. 3. Enzyme II, which is probably of lysosomal origin, is 90% inhibited by 20 mm l-(+)tartrate. Enzyme III is insensitive to tartrate but is completely inhibited by 10 µm p-chloromercuribenzoate, and I displays an intermediate sensitivity to tartrate. Both I and II, but not III, are also inhibited by molybdate and fluoride. 4. Whereas enzymes I and II appear to be typical nonspecific acid phosphohydrolases, enzyme III is atypical in that most of the common phosphate esters are poor substrates. It is further distinguished by a stimulatory response to purines and an apparent allosteric type inhibition by pyridoxine 5-phosphate.