Stereochemical aspects of the interaction of myosin and actomyosin with nucleotides.

The five possible analogues of ATP and the three possible analogues of ADP which contain single non-bridging sulphur atoms instead of oxygen in the polyphosphate structure have been used as probes of the interaction of nucleotides with myosin and actomyosin. Evidence is presented for the requirement of an alpha, beta, gamma-tridentate complex of magnesium and ATP as the substrate for myosin. Of the four possible tridentate MgATP diastereomers, the delta exo isomer (nomenclature of Cornelius & Cleland, 1978) appears to be the actual substrate.