Studies on the Alkali Light Chains of Vertebrate Skeletal Muscle Myosin

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Abstract
The structures of the alkali L chain subunits A1 and A2 were studied by examining the effect of the conformationally sensitive reagent tetranitromethane, which reacts specifically with tyrosyl residues. Whereas reaction in the presence of 6 M guanidine hydrochloride results in modification of the 3 tyrosyl residues of both these L chains, only 2 tyrosyl residues are exposed to the reagent in the native conformations of these proteins. By gel chromatography of the CNBr-cleaved chains, it was demonstrated that the 2 reactive tyrosyls are those located in the CB-1 and CB-3 segments and that these tyrosyl residues are modified simultaneously and not sequentially. The unreactive tyrosyl residue is in the CB-6 segment and is separated by 2 residues from the single cysteinyl residue of these chains. The modified L chains cannot be made to reassociate with the H chains by the NH4Cl hybridization procedure or by the thermal hybridization procedure. Reduction of the nitrotyrosyl groups to aminotyrosyl residues by sodium dithionite does not restore this effect. Regions of the L chains at CB-1 and CB-3 are involved in the association to the H chains.