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. 1967 Mar;102(3):917-21.
doi: 10.1042/bj1020917.

Inhibition of the orthophosphatase and pyrophosphatase activities of human alkaline-phosphatase preparations

R H Eaton  1 , D W Moss
Affiliations

Inhibition of the orthophosphatase and pyrophosphatase activities of human alkaline-phosphatase preparations

R H Eaton et al. Biochem J. 1967 Mar.

Abstract

1. Inhibition of the pyrophosphatase and orthophosphatase activities of human liver and small-intestinal alkaline-phosphatase preparations by different classes of inhibitors has been studied. 2. Each type of substrate, pyrophosphate or orthophosphate, is a competitive inhibitor of hydrolysis of the other type. 3. l-Phenylalanine is a non-competitive inhibitor of both types of activity of the intestinal preparation, but inhibits neither activity of the liver enzyme. Arsenate is a competitive inhibitor of both activities of both preparations. For a given inhibitor, the values of K(i) are independent of the type of substrate used when measurements are made at the same pH. 4. Mg(2+) ions activate orthophosphatase but inhibit pyrophosphatase, except in very low concentrations. 5. These results are compatible with the presence in each tissue preparation of a single enzyme with one type of active centre, possessing both orthophosphatase and pyrophosphatase activities.

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