title: A study to see whether phosphatidylserine, partial proteolysis and EGTA substitute for calmodulin during activation of the Ca2+-ATPase from red cell membranes by ATP.
abstract: (1) The effects of treatments that mimic calmodulin in increasing the apparent affinity for Ca2+ were tested to see whether, like calmodulin, they also change the activation of the Ca2+-ATPase from human red cell membranes by ATP at the low-affinity site. (2) Short incubations with either trypsin or acidic phospholipids such as phosphatidylserine increased the apparent affinity for ATP at the low-affinity site. (3) Under conditions in which it increased the apparent affinity of the Ca2+-ATPase for Ca2+, EGTA failed to change the activation by ATP. (4) As in calmodulin-bound Ca2+-ATPase, compound 48/80 inhibited the activity of the enzyme in the presence of phosphatidylserine by lowering the 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 maximum activity, leaving the apparent affinity of the enzyme for ATP at the low-affinity site unaltered. (6) Inhibition of the Ca2+-ATPase by compound 48/80 in the absence of calmodulin suggests that the inhibitor can act directly on the enzyme.
authors.affiliation: Instituto de Química y Fisicoquímica Biológicas (UBA-CONICET), Facultad de Farmacia y Bioquímica, Junín Buenos Aires, Argentina.
authors.forename: J P
authors.initials: JP
authors.lastname: Rossi
authors.forename: A F
authors.initials: AF
authors.lastname: Rega
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology; D000328:Adult; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000097:blood*; D002147:Calmodulin / Q000502:physiology*; D004533:Egtazic Acid / Q000494:pharmacology*; D004789:Enzyme Activation; D004910:Erythrocyte Membrane / Q000201:enzymology*; D006801:Humans; D010718:Phosphatidylserines / Q000494:pharmacology*; D014357:Trypsin / Q000378:metabolism*; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D010718:Phosphatidylserines; D003189:p-Methoxy-N-methylphenethylamine; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D014357:Trypsin; D000252:Calcium-Transporting ATPases