The plasma membrane Ca2+ pump catalyzes the hydrolysis of ATP at low rate in the absence of Ca2+.
The plasma membrane Ca2+ ATPase catalyzed the hydrolysis of ATP in the presence of millimolar concentrations of EGTA and no added Ca2+ at a rate near 1.5% of that attained at saturating concentrations of Ca2+. Like the Ca-dependent ATPase, the Ca-independent activity was lower when the enzyme was autoinhibited, and increased when the enzyme was activated by acidic lipids or partial proteolysis. The ATP concentration dependence of the Ca2+-independent ATPase was consistent with ATP binding to the low affinity modulatory site. In this condition a small amount of hydroxylamine-sensitive phosphoenzyme was formed and rapidly decayed when chased with cold ATP. We propose that the Ca2+-independent ATP hydrolysis reflects the well known phosphatase activity which is maximal in the absence of Ca2+ and is catalyzed by E(2)-like forms of the enzyme. In agreement with this idea pNPP, a classic phosphatase substrate was a very effective inhibitor of the ATP hydrolysis.
Mazzitelli
Luciana R
LR
IQUIFIB-Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina.
Rinaldi
Débora E
DE
Corradi
Gerardo R
GR
Adamo
Hugo P
HP
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004533:Egtazic Acid / Q000378:metabolism; D004912:Erythrocytes / Q000201:enzymology; D006868:Hydrolysis; D013552:Swine
D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium