A study to see whether phosphatidylserine, partial proteolysis and EGTA substitute for calmodulin during activation of the Ca2+-ATPase from red cells by ATP

58. ROSSI J.P.F.C. Y REGA, A.F.

BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1989 vol. 996 p. 153 - 159

0005-2736

(1) The effects of treatments that mimic calmodulin in increasing the apparent affinity for Ca z+ were tested to seewhether, like calmodulin, they also change the activation of the Ca z +-ATPase from human red cell membranes by ATPat the low-affinity site. (2) Short incubations with either trypsin or acidic phospholipids such as phosphatidylserineincreased the apparent affinity for ATP at the low-affinity site. (3) Under conditions in which it increased the apparentaffinity of the CaZ+-ATPase for Ca 2+, EGTA failed to change the activation by ATP. (4) As in calmedulin-boundCaZ+-ATPase, compound 48/80 inhibited the activity of the enzyme in the presence of phosphatidylserine by loweringthe apparent affinity for ATP at the low-affinity site, leaving the maximum velocity of the enzyme unaltered. (5)Compound 48/80 also inhibited the Ca2+-ATPase after partial proteolysis, but in this case it lowered the maximumactivity, leaving the apparent affinity of the enzyme for ATP at the low-affinity site unaltered. (6) |nhibition of theCaZ+-ATPase by compound 48/80 in the absence of calmodulin suggests that the inhibitor can act directly on theenzyme.