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Clinical Chemistry, Vol 38, 377-380, Copyright © 1992 by American Association for Clinical Chemistry
GY Han, XH Fan, XB Jin and DP Wang
Jinan Institute of Military Medicine, ShanDong, People's Republic of China.
An enzyme capable of hydrolyzing 4-methylumbelliferyl phenylphosphonate to 4-methylumbelliferone and phenylphosphonic acid has been detected in human serum. It has a Km value of 1.72 x 10(-4) mol/L, has an optimum pH of 8.8-9.1 in Tris buffer, and shows maximum activity at 60 degrees C (30 min). The enzymic activity can be inhibited by Na3PO4, EDTA, and cysteine. We saw no effect of CuSO4, adenosine, thymidine, NaN3, diethyl p-nitrophenyl phosphate, p-chloromercuribenzoate, isopropyl fluorophosphate, or eserine on the enzymic activity. The enzyme cannot hydrolyze substrates of phosphodiesterase I or alkaline phosphatase. The enzyme is considered a phosphonate esterase.
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