Finally the present results indicate that polyphloretin phosphate, polyphlorrhizin phosphate and polyhesperidin phosphate as well as polyoestradiol phosphate inhibit seminal acid phosphatase. These polymeric phosphates inhibit other enzymes as well (Diczfalusy et at. 1953, Ferno et al. 1953, 1958. It is thus very likely that the inhibition of acid phosphatase by these compounds is just an example of a widespread and non-specific action of high molecular-weight polyelectrolytes on several enzymes, as suggested by Spensley & Rogers (1954). The reversibility of the enzyme inhibition also suggests a macro-anion-macro-cation interrelationship similar to that postulated by these authors for the interaction between polyphloretin phosphate and protamine on hyaluronidase or between heparin and polylysine on pepsin. SUMMARY 1. The hydrolysis of monophenyl phosphate by unpurified human seminal acid phosphatase has been investigated.2. The optimum pH was found to lie between 5*4 and 5X7 and was not influenced by the substrate concentration.3. The Michaelis constant was estimated at several pH values. At the optimum pH a Km value of 0 18 mm was repeatedly found. High substrate concentrations did not inhibit the enzyme activity.4. Polyoestradiol phosphate was found to be a powerful, non-competitive inhibitor of seminal acid phosphatase. The inhibitory effect was strongest on the acid side of the pH optimum. The inhibition could be reversed by small amounts of protamine sulphate.5. The enzyme was also inhibited by polymeric phosphates of phloretin, phlorrhizin and hesperidin.The inhibition by polyphloretin phosphate was non-competitive.6. The trypanocide suramine proved to be a non-competitive inhibitor of seminal acid phosphatase.We are indebted to Dr E. Nordlander, Head of the Division of Fertility at the Department of Women's Diseases, for his helpful co-operation in obtaining semen specimens. Thanks are also tendered to AB Leo, Halsingborg, for a generous gift of polyphosphate analogues.
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