American Journal of Clinical Nutrition, Vol 27, 1117-1129, Copyright © 1974 by The American Society for Clinical Nutrition, Inc.

Creatine kinase and myofibrillar proteins in hereditary muscular dystrophy and vitamin E deficiency

¹ From the Department of Biochemistry, St. Louis University School of Medicine, St. Louis, Missouri 63104

Although the myopathy of vitamin E deficiency imitates many features of hereditary muscular dystrophy, the molecular basis of these similarities remains unexplained. Unlike the water-soluble vitamins that act as coenzyme precursors in mammalian tissues, the fat-soluble vitamins appear to regulate the synthesis of specific proteins required by highly differentiated organisms. To test the hypothesis that vitamin E does regulate the synthesis of specific proteins required for normal muscle function, a series of studies has been carried out in my laboratory to examine general protein synthesis and the synthesis of creatine kinase and selected myofibrillar proteins in vitamin E deficiency and hereditary muscular dystrophy in animals. Creatine kinase was selected for a number of studies because it has served as a marker for the onset of dystrophy in a variety of animals and man. It was shown by isotope-labeling studies of the purified enzyme from muscle in vitamin E-deficient rabbits, that the turnover rate was twice as great as that for the normal enzyme. Electron-microscopic studies of muscle from vitamin E-deficient rabbits, furthermore, showed that myofibrillar degradation and synthesis was occurring in the presence of an enhanced number of ribosomes. It was found that the yield of polysomes per gram of vitamin E-deficient muscle was 4 times higher than that from corresponding controls. Total muscle RNA levels were 2 to 3 times higher with increased muscle RNase. There appeared to be no differences in the intrinsic protein synthetic activity between normal and vitamin E-deficiency ribosomes. Because of reports of abnormalities in isoenzyme distribution of creatine kinase in human dystrophy and in hereditary dystrophy in the mouse, it was decided to investigate the nature of the creatine kinase occurring in vitamin E deficiency and in hereditary muscular dystrophy in the New Hampshire Red chick. The enzyme was purified to homogeneity from each source. It was found that the essential SH groups of the enzyme from dystrophic animals was highly labile to oxidation during the isolation process of the enzyme in contrast to vitamin E-deficient and normal chicks. This lability could be prevented by addition of dithiothreitol. Enzymes from normal, vitamin E-deficient, and dystrophic animals were similar in size, shape, charge, number of essential SH groups and kinetic properties. There were, however, some differences in the nature of the tryptic peptides obtained from the dystrophic enzyme.