MYOSIN HEAVY-CHAIN CONCENTRATION, SYNTHESIS RATE AND DEGRADATION RATE IN NORMAL AND DYSTROPHIC CHICKEN MUSCLE-CELLS IN CULTURE

Abstract

Myosin H chain concentrations, synthesis rates and degradation rates were studied in muscle cell cultures prepared from the breast muscle of 13-day normal (white leghorn) and dystrophic (line 307) chicken embryos. Muscle cells were studied after 7 days in culture, at which time they had reached a steady state with respect to myofibrillar protein synthesis and degradation. The quantity of myosin H chain was 10.5 .+-. 0.9 .mu.g/culture (n = 32) in normal cells and 8.10 .+-. 1.2 .mu.g/culture (n = 31) in dystrophic cells. The myosin H chain synthesis rate was 23,500 molecules/min per nucleus in normal cells and 39,900 molecules/min per nucleus in dystrophic cells, as determined by pulse labeling with [3H]Leu and measurement of the specific radioactivity of tRNA precursor pools. Myosin H chain half-lives rates were calculated to be 30.6 h in normal cells and 15.6 h in dystrophic cells when corrections were made for reutilization of [3H]Leu. Dystrophic muscle cultures accumulate less myosin H chain, despite their faster synthesis rate, because of faster degradation of myosin H chain.