Effect of nucleotide binding on the proximity of the essential sulfhydryl groups of myosin. Chemical probing of movement of residues during conformational transitions
The reaction of myosin with 3 bifunctional sulfhydryl reagents of differing cross-linking span is reported. In the absence of nucleotide only p-N,N''-phenylenedimaleimide with a cross-linking span of 12-14 .ANG. can bridge between the 2 essential sulfhydryls of myosin. The other 2 reagents, 2,4-dinitro-1,5-difluorobenzene and 4,4''-difluoro-3,3''-dinitrodiphenyl sulfone with cross-linking spans of 3-5 and 7-10 .ANG., respectively, react under identical conditions with the SH1 sulfhydryl but do not bridge to the SH2 group. In the presence of MgADP, both p-N,N''-phenylenedimaleimide and 4,4''-difluoro-3,3''-dinitrodiphenyl sulfone bridge across the SH1 and SH2 groups indicating a closer proximity of these 2 sulfhydryls in the presence of bound nucleotide. These results are discussed in relation to the conformational change induced in myosin by binding of the nucleotide.