The effect of calmodulin on the phosphoprotein intermediate of Mg2+-dependent Ca2+-stimulated adenosine triphosphatase in human erythrocyte membranes
- 14 February 1981
- journal article
- research article
- Published by Portland Press Ltd. in Biochemical Journal
- Vol. 194 (2) , 481-486
- https://doi.org/10.1042/bj1940481
Abstract
The effect of calmodulin on the formation and decomposition of the Ca2+-dependent phosphoprotein intermediate of the (Mg2+ + Ca2+)-dependent ATPase in erythrocyte membranes was investigated. In the presence of 60 .mu.M-Ca2+ and 25 .mu.M-MgCl2, calmodulin (0.5-1.5 .mu.g) did not alter the steady-state concentration of the phosphoprotein but increased its rate of decomposition. Higher calmodulin concentrations significantly decreased the steady-state concentration of phosphoprotein. Calmodulin (0.5-1.7 .mu.g) increased Ca2+-transport ATPase activity by increasing the turnover rate of its phosphoprotein intermediate. Increasing the MgCl2 concentration from 25 .mu.M to 250 .mu.M increased the (Mg2+ + Ca2+)-dependent ATPase activity but decreased the concentration of the phosphoprotein intermediate. Similarly to calmodulin, MgCl2 increased the turnover rate of the Ca2+-transport ATPase complex (about 3-fold). At the higher MgCl2 concentration calmodulin did not further affect the decompositon of the phosphoprotein intermediate. Apparently, calmodulin and MgCl2 increase the turnover of the Ca2+-pump by enhancing the decomposition of the Ca2+-dependent phosphoprotein intermediate.This publication has 23 references indexed in Scilit:
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