Myosin subunit interactions. Localization of the alkali light chains.

Myosin homodimers, molecules containing either the A1 or the A2 light chain, do not exchange their light chains under conditions approximating physiological temperature and ionic strength. Myosin heterodimers, molecules containing both A1 and A2 light chains, are therefore formed at the time of synthesis rather than by a labile subunit exchange. Antibodies specific for the amino-terminal region of the alkali light chains were used to localize these subunits in myosin by immunoelectron microscopy. The close proximity of the alkali light chain to the 5,5'-dithiobis-(2-nitrobenzoic acid) light chain in the "neck" region of the myosin head is consistent with the finding that the 5,5'-dithiobis-(2-nitrobenzoic acid) light chain influences subunit interactions between the alkali light chain and heavy chain in vertebrate skeletal muscle myosin.