Abstract
1. The two isozymes of alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) detectable in human blood group O plasma have been separated from one another and isolated in a high state of purity. With p-nitrophenyl phosphate as substrate, the catalytic properties of the two isozymes appear to be the same with respect to pH optimum, 10.5; Km, 0.35–0.4 mM, and activity in the presence of EDTA, Mg2+ and Zn2+. The isozymes differ in their electrophoretic mobilities and in their reactivity in the presence of activators and inhibitors. l-Phenylalanine specifically inhibits the minor isozyme. 2. Comparison of the isozymes isolated from plasmas of individuals of different phenotype indicates that the major isozyme is the same in A, B and O. The minor isozymes of B and O appear to be identical, but they both differ from the minor isozyme detectable in A individuals. Although separable electrophoretically on acrylamide disc electrophoresis and on DEAE-cellulose columns, the minor isozyme from group A individuals appears to have the same catalytic properties as the major component from group A plasma.
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