Aorta caldesmon inhibits actin activation of thiophosphorylated heavy meromyosin Mg2+-ATPase activity by slowing the rate of product release.
Activation of aorta thiophosphorylated heavy meromyosin (HMM[SP]) Mg2+-ATPase activity by aorta actin and the fraction of HMM[SP]-substrate intermediate complexes bound to actin were measured simultaneously. At 25 degrees C the Km for ATPase activation and the dissociation constant for the binding reaction were similar, irrespective of the presence or absence of tropomyosin. Aorta caldesmon (0.1 mol/mol actin) inhibited ATPase activation by 80-90% but did not alter the binding of HMM[SP]-product intermediates to actin. It is concluded that caldesmon inhibits by slowing the rate-limiting release of products from the actin-HMM[SP].ADP.Pi complex.
Marston
S
S
Cardiac Medicine, Cardiothoracic Institute, London, England.
D000199:Actins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001011:Aorta / Q000378:metabolism*; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism*; D010766:Phosphorylation; D012756:Sheep
D000199:Actins; D002148:Calmodulin-Binding Proteins; D015879:Myosin Subfragments; D017301:Ca(2+) Mg(2+)-ATPase