Abstract
Isotope-exchange reactions (H2(18)O in equilibrium with KH2PO4) during ATP hydrolysis catalyzed by myosin and its subfragment 1 from rabbit, dog, and human cardiac muscle were studied. All preparations of myosin and subfragment 1 in the presence of Mg2+ catalyzed two types of 18O-exchange reactions similar to those of skeletal muscle: intermediate and direct 18O exchange. The dependences of both reactions on divalent metals and nucleotides were studied. Data on 18O exchange of subfragment 1 from rabbit, dog, and human cardiac muscle were obtained for the first time. They indicate the similarity of molecular mechanisms of ATP energy use in cardiac and skeletal muscle contraction.
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