A method for measuring the catalytic activity of small intestine type alkaline phosphatase using L-phenylalanine as an inhibitor

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Electrophoresis with cellulose-acetate membrane has been used as a convenient method to detect isozymes of alkaline phosphatase (ALP) such as small intestine-type ALP (SI-ALP) and bone type ALP. It is, however, desirable to develop a quantitative method in which ALP types can distinctively be detected. We developed a method for measuring the catalytic activity of SI-ALP by an inhibiting method using L-phenylalanine.<BR>Using a reagent recommende d by the JSCC transferable method for ALP, the catalytic activities of both liver and bone type ALPs were inhibited by 53% in the presence of 50mmol/l of L-phenylalanine at the final concentration, whereas the activity of SI-ALP was inhibited by 95%, indicating the degree of inhibition for SI-ALP was higher than liver and bone type ALPs. When we tested the recombinant ALP of human liver type, "TraceCalib, Kanto Chemical Co., Inc., Tokyo" which is a calibrator for the transferable method, similar results to those of liver and bone type ALPs were obtained. These results indicate that the inhibiting assay method using L-phenylalanine is useful for evaluating SI-ALP activity, which mostly corresponded to the activities inhibited by the presence of L-phenylalanine out of the total ALP activity of an assay sample. We believe that our method is convenient for measuring the catalytic activity of SI-ALP and excellent regarding its quantitativeness, ease of manipulation, and general usefulness.