AJP - Gastrointestinal and Liver Physiology, Vol 238, Issue 1 3-G9, Copyright © 1980 by American Physiological Society

ARTICLES

Anion-stimulated phosphohydrolase activity of intestinal alkaline phosphatase

M. H. Humphreys, G. A. Kaysen, L. Y. Chou and J. B. Watson

Phosphohydrolase activity of a highly enriched commercial preparation of calf intestinal alkaline phosphatase was stimulated in the presence of HCO3. SO4, Cl, SCN, and acetate did not stimulate hydrolysis, whereas SO3 exhibited a bimodal effect, stimulating at low (25mM) concentration but inhibiting at high (100 mM) concentration. The pH optimum of this stimulation by HCO3 or SO3 was 8.5--9.0 and was maximal at a Mg concentration of 0.5 mM. HCO3 increased the Vmax of the reaction without changing the Km for ATP. ATP, GTP, UTP, and xanthosine triphosphate were equally effective as substrates, whereas AMP and p-nitrophenyl phosphate were much less effective. Alkaline phosphatase activity was inhibited by L-cysteine and L-phenylalanine, compounds that also inhibited the HCO3-ATPase activity of the preparation. Passage of the commercial preparation through an anion-exchange column yielded a fraction with enriched alkaline phosphatase and HCO3-ATPase activities; this fraction proved to be a single protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, on isoelectric focusing, and by immunologic techniques. These studies strongly suggest that alkaline phosphatase and anion-stimulated phosphohydrolase activities are properties of the same protein in small intestine. It is possible that alkaline phosphatase may function as a HCO3-ATPase involved in intestinal absorption and secretion.

This article has been cited by other articles:

				Y. Akiba, M. Mizumori, P. H. Guth, E. Engel, and J. D. Kaunitz Duodenal brush border intestinal alkaline phosphatase activity affects bicarbonate secretion in rats Am J Physiol Gastrointest Liver Physiol, December 1, 2007; 293(6): G1223 - G1233. [Abstract] [Full Text] [PDF]