The zinc-stimulated acid and neutral p-nitrophenyl phosphatase activities of chick liver and duodenum

Abstract

1. 1.|Some properties of the soluble Zn 2+-stimulated p-nitrophenyl phosphatases active at acid and neutral pH have been studied with (NH 4) 2SO 4-precipitated preparations from the soluble cytoplasm fraction of homogenates from chick liver, duodenum and metanephros. Analogous Zn 2+-stimulated phosphatase activity was not found in the particulate fraction from these tissues or in any fraction from homogenates of chick brain or heart muscle. 2. 2.|The pH optima of these soluble, Zn 2+-stimulated enzymes were at pH 4.9, 6.2 and 6.7, respectively, for duodenum, liver and metanephros. The enzymes responsible for the low level of soluble activity without added Zn 2+ or with added Mg 2+ showed maximal activity at pH 5.4–5.8 in all three tissues. 3. 3.|The soluble Zn 2+-stimulated p-nitrophenyl phosphatase enzymes of liver and duodenum were similar in most other properties examined. With preparations from both tissues, a marked (10- to 20-fold) stimulation of p-nitrophenyl phosphatase activity was elicited only by Zn 2+, but Mg 2+, Mn 2+ and Co 2+ caused some stimulation. The optimal concentration of Zn 2+ varied over the range 3–10 mM, depending on pH and type of buffer used. A marked and specific stimulatory effect of Zn 2+ was seen only for hydrolysis of p-nitrophenyl phosphate, of the many phosphate compounds tested. Hydrolysis of ATP by these preparations was moderately stimulated by both Mg 2+ and Zn 2+. Indirect evidence suggests that the Zn 2+-stimulated hydrolysis of p-nitrophenyl phosphate was not due to the inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1), fructose-1,6-diphosphatase (fructose-1,6-diphosphate 1-phosphohydrolase, EC 3.1.3.11), or ATPase (ATP phosphohydrolase, EC 3.6.1.3) present in these preparations.