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The binding interaction between myosin subfragment 1 isozymes with immobilized nucleotide, where they show differential behavior, has been examined. By employing subfragment 1 hybrids formed by crosses between heavy and alkali light chains, it is possible to demonstrate that the differential behavior is modulated by the alkali light chain component of the protein and not by differences in the heavy chain subunits in these isozymes resulting from the proteolytic treatment used in their formation. The fact that the free alkali light chains show weak differential binding under these conditions suggests that the binding in the case of the subfragment 1 isozymes may occur at a site distinct from the ATPase site. This was substantiated by examining the behavior of subfragment 1 containing 14C MgADP noncovalently trapped in the ATPase site by the bifunctional reagent N, N-p-phenylenedimaleimide, on agarose-ATP. The data suggest that different ATP binding domains may be operating in myosin depending on the ionic conditions being employed.
Burke et al. (1981) studied this question.