CADMIUM ION IS A NONCOMPETITIVE INHIBITOR OF RED-CELL CA2-ATPASE ACTIVITY()

In the presence as well as in the absence of calmodulin, Cd2+ inhibits the human erythrocyte plasma membrane Ca2+-ATPase activity non-compet itively with K(i) = 2 nM, whereas ATP-dependent Ca2+-transport across the red cell membrane was found to be inhibited competitively by Cd2(Verbost, P.M., Flik, G., Pang, P.K.T., Lock, R.A.C. and Wendelaar Bon ga, S.E. (1989) J. Biol. Chem. 264, 5613-5615). In this study it will be argued that Cd2+ also inhibits Ca2+-transport non-competitively, an d that the discrepancy with previous conclusions most probably relies on use of an incorrect computer program that calculates the free conce ntrations of Ca2+ and Cd2+ at the experimental conditions applied for measurement of Ca2+ uptake.