The Ca2+-pumping ATPase of heart sarcolemma. Characterization, calmodulin dependence, and partial purification.
The (Ca2+ + Mg2+) ATPase of dog heart sarcolemma (Caroni, P., and Carafoli, E. (1980) Nature 283, 765-767) has been characterized. The enzyme possesses an apparent Km (Ca2+) of 0.3 +/- 02 microM, a Vmax of Ca2+ transport of 31 nmol of Ca2+/mg of protein/min, and an apparent Km (ATP) of 30 microM. It is only slightly influenced by monovalent cations and is highly sensitive to orthovanadate (Ki = 0.5 +/- 0.1 microM). The high vanadate sensitivity has been used to distinguish the sarcolemmal and the contaminating sarcoplasmic reticulum Ca2+-dependent ATPase in heart microsomal fractions. Calmodulin has been shown to be present in heart sarcolemma. Its depletion results in the transition of the Ca2+-pumping ATPase to a low Ca2+ affinity; readdition of calmodulin reverses this effect. The Na+/Ca2+ exchange system was not affected by calmodulin. The results of calmodulin extraction can be duplicated by using the calmodulin antagonist trifluoperazine. The calmodulin-depleted Ca2+-ATPase has been solubilized from the sarcolemmal membrane and "purified" on a calmodulin affinity chromatography column. One major (Mr = 150,000) and 3 minor protein bands could be eluted from the column with ethylene glycol bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid (EGTA). The major protein band (72%) has Ca2+-dependent ATPase activity and can be phosphorylated by [gamma]32P]ATP in a Ca2+-dependent reaction.
D000818:Animals; D001921:Brain; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000302:isolation & purification / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology*; D002417:Cattle; D004285:Dogs; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D012508:Sarcolemma / Q000201:enzymology*; D014639:Vanadium / Q000494:pharmacology
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D014639:Vanadium; D000252:Calcium-Transporting ATPases