Functional regions in the essential light chain of smooth muscle myosin asrevealed by the mutagenesis approach

The endogenous essential light chain (LC17) of myosin from intestine smooth muscle was replaced with mutated essential light chains prepared using rec ombinant techniques. Complete exchange was observed with histidine-tagged d erivatives of LC17a, LC17b and E122A-LC17a (LC17a and LC17b are the usual c onstituants of smooth muscle myosin), with small changes in the ATPase acti vity of reconstituted myosins. Much less exchange was observed with the lig ht-chain derivative lacking the last 12 amino acid residues, demonstrating the importance of this segment, which may act as one arm of a pair of pince rs to bind the myosin heavy chain.