Sreter et al. (1) observed that the Ca2+ transport function of the FSR
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was impaired in the muscles of dystrophic animals. Previous work in this laboratory (2, 3) confirmed the discovery of Sreter and further showed that the lipid composition of the FSR obtained from the dystrophic chickens was different from FSR of normal controls. In this study experimental evidence has been obtained that the Ca2+-activated ATPase enzyme in the FSR of the dystrophic chickens is also different from that of the normal control. On the other hand, no alterations were found in the activity of the natural tropomyosin (tropomyosin plus troponin) in the muscles of the dystrophic chickens.
Materials and Methods. All reagents used were of analytical grade. Chickens inflicted with genetically controlled muscular dystrophy were obtained from the Department of Avian Sciences of the University of California, Davis, CA. The FSR was prepared using the method of Martonosi and Feretos (4), and the natural tropomyosin was isolated by the method of Ebashi and Ebashi (5). The yield of natural tropomyosin from the breast muscles of both the normal and the dystrophic chicken (2 mg natural tropomyosin per g of muscle protein) was approximately the same. Troponin-free actin was prepared according to the method of Bailin and Barany (6), and myosin A and myosin B were prepared as described by Mommaerts (7). The ATPase enzyme of the FSR was solubilized by the method of Ikemoto et al. (8) except that we omitted glycerol from the mixtures. The ATPase activity was measured as described previously (3) except that the incubation time was 1 min. The composition of each assay mixture will be specified in the text.
Results. The Ca2+-activated “extra” ATPase activity was studied first using the FSR of the normal and the dystrophic chickens as the source of the enzyme.
