HISTOCHEMICAL STUDIES ON THE EFFECT OF ANIONS ON ALKALINE PHOSPHOMONOESTERASE ACTIVITY

Pretreatment of cryostat sections of dog kidney with sodium salts of various anions in acetate buffer at pH 4.0 for periods of time ranging up to 6 hours produces differential inhibition of non-specific alkaline phosphatase activity as determined by the Gomori method. The degree of anionic effect is dependent on the nature of the anion and modified by the cation present. The effect also varies directly with the anionic concentration, duration of exposure and temperature of the pretreatment buffer and inversely with the pH. On the basis of the differential suppression of enzymatic activity by the various anions, and the conditions under which these effects were evident, distinctive inhibition profiles were established for the several phosphomonoesterases tested, including the renal and intestinal alkaline phosphatases and the smooth muscle 5'-nucleotidases of several species. The similarity of the results obtained in various biochemical studies on other enzymes reported in the literature and those obtained histochemically in these experiments suggests a common mechanism of action; this is presumed to be a differential effect of anions on the dissociation of apoenzyme and coenzyme. The method described provides a simple and effective means of differentiating, under histochemical conditions, closely related and even apparently identical enzymes.