Alkaline phosphatase and ATPases in brush-border membranes of rat jejunum: Distinct effects of divalent cations and of some inhibitors

Abstract

The effects of divalent cations and of some inhibitors on the activities of alkaline phosphatase and ATPase were examined in rat jejunal brush-border membranes (BBM) isolated by tha Ca(2+)-(BBMCa) or the Mg(2+)-precipitation method (BBMMg). Similar results were found in BBMCa and BBMMg though generally higher in BBMCa. Alkaline phosphatase activity was stimulated by 5 mM MgCl2 (30% to 44%), but not by 5 mM CaCl2 or 0.1 mM ZnCl2, at pH 9.5 or 7.4. ATPase activity was equally stimulated by 5 mM MgCl2 and by 5 mM CaCI2 (about 150%). Alkaline phosphatase activity was significantly inhibited by 1 mM vanadate, 5 mM diamox, 5.0 mM L-leucine and 1 mM theophylline. In contrast, Ca(2+)-ATPase and Mg(2+)-ATPase activities were not depressed by those alkaline phosphatase inhibitors, but were inhibited by 0.1 mM trifluoperazine (more than 70%). 0.1 mM ZnCl2 also appeared to be inhibitory to Ca(2+)-ATPase and Mg(2+)-ATPase, but not to alkaline phosphatase activity even in the presence of Ca2+ and Mg2+. These results suggest that Ca(2+)-ATPase and Mg(2+)-ATPase activities of the rat jejunal BBM are not merely manifestations of alkaline phosphatase, but rather belong to (a) distinct enzyme(s).

Identification of thiamine monophosphate hydrolyzing enzymes in chicken liver

“…Хотя, как известно, ЩФ -это цинксодержащий энзим, для полного проявления его активно-сти необходимо присутствие ионов Mg 2+ [17]. Стимулирующий эффект Mg 2+ был установлен для препаратов ЩФ из различных источников [28][29][30][31]. В каталитическом механизме ЩФ E. coli роль катионов Mg 2+ состоит в координации мо-лекулы воды, обеспечивающей протонирование/ депротонирование остатка Ser-102 [32].…”

“…В каталитическом механизме ЩФ E. coli роль катионов Mg 2+ состоит в координации мо-лекулы воды, обеспечивающей протонирование/ депротонирование остатка Ser-102 [32]. В то же время ионы Ca 2+ не влияют на активность ЩФ [28,33]. Аналогичные закономерности наблюда-ются при гидролизе TMP при рН 9,0 (рис.…”

Effects of Concanavalin A on intestinal brush border enzyme activity in broiler chickens

“…Alkaline phosphate (EC 3.1.3.1) activity was assayed by a modification of the method of Wang and Gilles-Baillien (1992). BBMV (20 ml) were incubated in the presence of 270 ml of 100 mM glycine pH 9Á5, 10 mM MgCl 2 , 0Á2 mM ZnCl 2 and 20 mM p-nitrophenylphosphate as substrate.…”

Evidence for P2-purinoceptor-mediated uptake of Ca2+ across a fish (Oreochromis mossambicus) intestinal brush border membrane

“…Because ATPase activity has been localized to the apical membrane mammalian intestinal cells [22][23][24][25][26][27], an investigation of the involvement of an ATPase in the uptake of Ca# + was warranted.…”