EXPRESSION OF HYBRID ISOMYOSINS IN HUMAN SKELETAL-MUSCLE

Myosin of human skeletal muscles was analyzed by means of several elec trophoretic techniques. Myosin heavy chain (HC)-IIa- and HC-IIb-based isomyosins were identified by pyrophosphate-polyacrylamide gel electro phoresis (PP-PAGE). The electrophoretic mobilities of these fast-twitc h muscle isomyosins differed in the order HC-IIa triplets < HC-IIb tri plets. To determine the subunit composition of myosin molecules that f unction in intact muscle, two-dimensional electrophoresis in which the first and second dimensions were PP-PAGE and sodium dodecyl sulfate-P AGE, respectively, was also performed. Slow-twitch muscle isomyosin co ntained, in addition to slow-twitch light chain (LC) and HC-l isoforms , appreciable amounts of LC-2f, HC-IIa, and HC-IIb isoforms, and fast- twitch muscle isomyosin consisted of LC-2s and RC-I isoforms as well a s fast-twitch LC and HC isoforms. Without consideration of HC- and slo w-twitch alkali LC heterodimers, at least 31 possible isomyosins are d erived from these findings on the subunit composition of isomyosins in human skeletal muscle.