Abstract: | The reaction of myosin with three 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 A can bridge between the two essential sulfhydryls of myosin. The other two 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 A, 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 two 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. |