Abstract
THE present view of the molecular mechanism of muscle contraction1 does not explain why myosin has two structurally similar globular heads2. Each of these heads can interact with actin and with ATP, and each seems to hydrolyse ATP at about the same rate3. To investigate possible functional differences between the two heads of myosin, we have compared the rates of intermediate oxygen exchange4–6 catalysed by heavy meromyosin (HMM), which has two heads, and subfragment 1(S1), which has one head, at different levels of actin activation. This oxygen exchange occurs between water and the γ-phosphoryl groups of two enzyme–nucleoside phosphate intermediates along the pathway of coupled ATP hydrolysis7. Thus, measurements of oxygen exchange can be used to probe the kinetics of intermediate steps in the hydrolytic and contractile mechanism. Any difference in the rate of oxygen exchange indicates either a difference in the lifetimes of the exchanging intermediates, or in the kinetic constants of the exchange reaction itself4–6,8.
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SHUKLA, K., LEVY, H. Evidence from oxygen exchange measurements for a cooperative interaction between the two heads of myosin. Nature 266, 190–191 (1977). https://doi.org/10.1038/266190a0
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DOI: https://doi.org/10.1038/266190a0
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