title: Myosin isozyme distribution in rodent hindlimb skeletal muscle.
abstract: The purpose of this study was to examine the distribution of myosin isozymes in rodent (Rattus norvegicus) hindlimb skeletal muscles and regions of muscle known to have contrasting fiber-type composition. Muscle samples were analyzed for Ca2+-regulated myofibril adenosine triphosphatase (ATPase) activity, Ca2+-activated myosin ATPase activity, myosin isozyme profile, and myosin light chain profile. Four isozymes of myosin were identified based on native protein and light chain electrophoresis patterns: one associated primarily with slow-twitch muscle (SM) and three associated primarily with fast-twitch muscle (FM). Multiple linear regression analysis of Ca2+-regulated myofibril ATPase activity (pCA 4) vs. measured isozyme profile was used to estimate the myofibril ATPase activities of the individual isozymes (FM1 = 0.86, FM2 = 0.52, FM3 = 0.31, and SM = 0.15 mumol Pi formed . mg myofibril protein-1 . min-1 at 25 degrees C, n = 180, P less than 0.001). Differences in the native isozyme profiles and myofibril ATPase activities between muscles and muscle regions of similar fiber type composition indicate that a given fiber type may not necessarily express a single isozyme profile. These data are consistent with the hypothesis that, among rodent hindlimb skeletal muscles and inherently their motor units, a range of myosin isozyme profiles exists that may provide a broad range of mechanical expression.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D005260:Female; D006614:Hindlimb; D007527:Isoenzymes / Q000378:metabolism*; D009132:Muscles / Q000201:enzymology*; D009210:Myofibrils / Q000201:enzymology; D009218:Myosins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D014018:Tissue Distribution
chemical_list: D007527:Isoenzymes; D000251:Adenosine Triphosphatases; D009218:Myosins