The study demonstrates a correlation between the biochemical O18 exchange reaction and the contractile process in myosin, suggesting shared active site amino acids.
Heavy meromyosin (H-meromyosin) in the presence of Mg/sup ++/ catalyzes the incorporation of O/sup 18/ from solvent water into the P/sub i/ released from adenosine triphosphate (ATP), dATP, and cytidine, inosine, uridine, and guanosine triphosphates. Tripolyphosphate under the same conditions does not undergo the O/ sup 18/ exchange reaction with either myosin or H-meromyosin. The H-meromyosin catalyzed O/sup 18/ exchange with Mg/sup ++/ ATP is independent of hydrogen ion concentration between pH 5.5 and pH 9.3. The ATPasedependence of H-meromyosin on divalent metal ion radius and on pH has been found to correspond to that of myosin systems. A rough correlation was found between the divalent metal ions required for contraction, for optimal O/sup 18/ exchange, and for strong complexing with ATP/sup -4/. A parallelism exists between the substrates giving the maximal amount of tension and those giving the maximal amount of exchange. It is suggested that some amino acids at the active site of myosin are common to the exchange reaction and the contractile process. (auth)
Yount et al. (Wed,) studied this question.