The study determines the binding constants and combining weights for ATP and ADP to myosins A and B, providing fundamental biochemical insights into muscle protein interactions.
Should not inform clinical decisions on contractile proteins; leaves open translation of myosin-ATP affinities to human cardiac models.
Values for binding of ATP and ADP to myosin B and ATP to myosin A were determined from mixtures of these nucleotides and proteins by use of rapid filtration to separate bound and unbound nucleotides and by use of an ATP-regenerating system (creatine phosphate-creatine phosphokinase). Calculation of the binding curves of ATP to 105 g of myosin B by the mass law binding expression using two sets of binding sites, n1 and n2, and with binding constants, k1=40×103 and k2=1.5×103 1/mole, respectively, yielded a curve of good fit to the experimentally determined points when n1=0.4 and n2=1.2 moles per 105g. Similar calculation of data from binding of ATP to myosin A yielded a curve of best fit when n1=0.5 and n2=3.0 per 105 g with k1=5,500 and k2=550 1/mole. At 1 mM ATP, myosin A bound 50% more than myosin B. ADP at 1 mM appeared to saturate myosin B about 97%. The amounts of ADP bound to myosin B fitted a curve with one value of n which equaled 0.36. Multiplication of 105g by the factors required to convert the above n values to integers yields combining weights of 250,000 and 200,000 for myosin B and myosin A.
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Bowen et al. (1968) studied this question.
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