Does calmodulin regulate the affinity of the human red cell Ca2+-pump for ATP?

55. CARIDE, A.J., ROSSI J.P.F.C., GARRAHAN, P.J AND REGA, A.F.

BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1990 vol. 1027 p. 21 - 24

0005-2736

(1) We have reexamined the effects of calmodulin and of the calmodulin antagonist, compound 48/80 on theinteraction of ATP at its low-affinity site in the Ca? -ATPase from human red cells. (2) At variance with our earlierproposal (Biochim. Biophys. Acta (1985) 816, 379-386) calmodulin increased the maximum effect of ATP withoutchanging the apparent affinity for ATP at the low-affinity site. Accordingly, ATP increased the maximum activation bycalmodulin without altering the apparent affinity of the Ca*+ -ATPase for calmodulin. (3) Confirming our previousobservation (Biochim. Biophys. Acta (1985) 816, 379-386) compound 48/M lowered the apparent affinity of theCa?+-ATPase for ATP at the low-affinity site. This has to be attributed to a direct effect of this compound on theenzyme rather than to its effect as calmodulin antagonist.