Effect of Duchenne muscular dystrophy on enzymes of energy metabolism in individual muscle fibers.

Individual muscle fibers from patients with Duchenne muscular dystrophy at an early stage in their disease, and from apparently normal boys of similar age, were analyzed for 13 enzymes of energy metabolism. This approach avoided the serious problems with muscle homogenate assays from increases in nonparenchymal components and permitted assessment of disease changes in different fiber types. Some enzymes of glycogenolysis (phosphorylase, phosphoglucomutase, and pyruvate kinase) were decreased in dystrophic fibers of all types. Phosphofructokinase was decreased in presumptive type II fibers. Lactate dehydrogenase was increased in type I fibers and essentially unchanged in type II. Phosphoglucoisomerase was near normal. Two enzymes of glucose metabolism not involved in glycogenolysis, hexokinase and glycogen synthase, were near normal, but a third, fructose bisphosphatase, was sharply reduced. Two enzymes of oxidative metabolism, citrate synthase, and beta-hydroxyacyl CoA dehydrogenase, were unchanged or increased. Two enzymes of high energy phosphate transfer, creatine kinase and adenylokinase, were only marginally affected. The net result is to leave the type II fibers, which normally exert the greatest force, with a severe deficit in the glycogenolytic enzyme machinery to maintain that force.