The expression of glycogen phosphorylase in normal and dystrophic muscle.

Specific cofactor labelling was employed to determine the degradation rate of glycogen phosphorylase in normal adult C57BL/6J mice and their dystrophic counterparts (C57BL/6Jdy/dy). The rate constant for the decay of phosphorylase-bound label was 0.125 day-1 in normal muscle and 0.49 day-1 in dystrophic muscle, i.e. a lower rate of catabolism of phosphorylase in dystrophic muscle. Quantitative Northern-blot analyses of total RNA isolated from normal and dystrophic muscle indicated that the abundance of phosphorylase mRNA as a percentage of total RNA was approx. 40% lower in dystrophic muscle. The specific activity of phosphorylase in dystrophic muscle is approx. 60% lower than in normal muscle, and is elicited by a lower rate of turnover of the enzyme, i.e. both synthesis and degradation are decreased.