The interaction of myosine S1 with phosphorothioates of ADP: An 18O exchange study by 31P NMR

The ¹⁸O exchange reaction which labeled P_i undergoes in the presence of complexes of myosin subfragment 1, MgCl₂, and the different phosphorothioates of ADP has been observed by ³¹P NMR. From these experiments it can be concluded that ADP and ADP (α-S) (A) on the one hand and ADP (β-S) and ADP (α-S) (B) on the other hand form similar complexes as far as the number of reversals of the nucleoside triphosphate formation step from the nucleoside diphosphate and P_i, is concerned. In addition, the same seems to hold for the rate constant k_?2, which describes the binding step of free P_i, to the subfragment 1 nucleoside diphosphate complex. These observations support former kinetic experiments which yielded the same similarities for the rate parameters describing association and dissociation of the subfragment 1 nucleotide complexes.