The calmodulin-binding domain as an endogenous inhibitor of the p-nitrophenylphosphatase activity of the Ca2+ pump from human red cells¨

23. CARIDE, A.J., PENNISTON, J.T. AND ROSSI J.P.F.C

BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1991 vol. 1069 p. 94 - 98

0005-2736

Digestion of red cell membranes with chymotrypsin elicited p-nitrophenylphosphatase activity. During digestion,the p-nitrophenylphosphatase appeared in parallel with the activation of the Ca2+.ATPase (in the absence of¢almodulin). The chymotrypsin-activated p-nitrophenyiphosphatase was inhibited by C20W, a 20 amino acidpeptide modelled after the sequlnce of the caimodulin.binding site of the red cell Ca 2+ pump (Vorherr et ai. (1990)Biochemistry 29, 355-36$). On the contrary, the (ATP + Ca2+).dependent p-nitrophenyiphosphatase activity ofintact red cell membranes was not affected by C20W. Ca 2+ inhibited the chymotuosin-induced p.nitrophenylphosphatase (K i for Ca 2+- 2 ~tM). In the absence of ATP, C20W and Ca 2+ did not interact inapparent affinity as inhibitors of this activity. On the other hand, in the presence of 2 mM ATP, Ca z + antagonizedthe inhibition produced by C20W. The results are consistent with the idea that the calmodulin.binding site is an'autoinhibitory domain' of the Ca 2+ pump, and that removal of this domain by proteolysis, or ~ts modification bycaimodulin binding is the reason for the activation of both the ATPase and the p-nitrophenyiphosphatase activity ofthe pump. The results presented in this paper give new informatio~ about the mechanism of the two kinds ofp-nitrophenylphosphatase and about the nature of the apparent competition between C20W and Ca z +.