Calmodulin stimulates both adenosine 5'-triphosphate hydrolysis and synthesis catalyzed by a cardiac calcium ion dependent adenosinetriphosphatase.
A Ca2+-dependent ATPase purified from a rabbit heart membrane preparation was compared to the Ca2+-dependent ATPase purified from skeletal muscle sarcoplasmic reticulum. The two ATPases display an identical electrophoretic pattern and an identical Ca2+-concentration dependence. However, only the cardiac preparation exhibits a 2-3-fold activation by calmodulin. This effect is best observed when the molar concentrations of calmodulin and ATPase are equivalent and in the presence of high Ca2+ (approximately 10(-5) M) and ATP (approximately 10(-3) M) concentrations. It is demonstrated for the first time that calmodulin stimulates the rate of ATP synthesis, as revealed by an increased production of Pi and a faster ATP in equilibrium Pi exchange, as well as the rate of ATP hydrolysis. It is also demonstrated that calmodulin activation is expressed with purified and detergent-solubilized enzyme in addition to membrane-bound systems. These findings indicate that the effect of calmodulin is an acceleration of the enzyme turnover, due to direct interaction of calmodulin with the enzyme.
D000255:Adenosine Triphosphate / Q000096:biosynthesis / Q000378:metabolism*; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology*; D006868:Hydrolysis; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D014268:Trifluoperazine / Q000494:pharmacology
D002147:Calmodulin; D014268:Trifluoperazine; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases