Isomyosins in human type 1 and type 2 skeletal muscle fibres.

Human myosin from different skeletal muscles was analysed in a non-denaturing gel system, and the isoenzyme composition correlated with the histochemical composition of the muscle. Two components (SM1 and SM2) were associated with type 1 (slow-twitch) fibres, and three (FM1, FM2 and FM3) with type 2 (fast-twitch) fibres. Light-chain analysis was performed in sodium dodecyl sulphate/polyacrylamide gels. There are three light chains (LCs1a, LCS1b and LCs2) in type 1 fibres, and three (LCf1, LCf2 and LCf3) in type 2 fibres. LCf1 and LCs1b co-migrate in sodium dodecyl sulphate gels. The ratio of LCf3/LCf2 is correlated with the distribution of the individual fast isoenzymes. These results explain apparent discrepancies in the literature concerning the light-chain distribution of human myosin.