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Abstract:
The 18O exchange reaction which labeled Pi 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 Pi, is concerned. In addition, the same seems to hold for the rate constant k−2, which describes the binding step of free Pi, 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.
