Comparison of the protein-synthesizing machinery in the skeletal muscle of normal and dystrophic Bar Harbor mice

Abstract

1. Although the total weight of leg muscle increased with the age of a normal mouse the DNA and RNA content per leg did not change significantly. 2. The weight of leg muscle from a dystrophic mouse was only about 45% of that from a normal mouse but the DNA and RNA contents were the same and hence similar DNA/RNA ratios were obtained. 3. The total ribosome contents of normal and dystrophic mice were the same on a whole-leg basis, and for both the free ribosomes were about 60% of the total. However, comparison with similar data from liver suggested that some loss of ribosomes occurred during the isolation procedure. 4. The polyribosome patterns obtained by density-gradient centrifugation were the same for normal and dystrophic muscle, and comparable polyribosome fractions of different sizes obtained from such gradients had similar capacities for the incorporation of radioactive amino acids in a standard protein-synthesizing system. 5. By using a standard protein-synthesizing system with normal polyribosomes similar extents of incorporation were found with normal- or dystrophic-muscle pH5 fraction or partially purified transfer RNA preparation. 6. It is concluded that there is no absolute difference between the protein-synthesizing systems of normal and dystrophic mouse muscle and that the observed apparent differences result from concentration differences caused by changes in muscle volume. 7. A possible cause of the failure of dystrophic muscle to resynthesize myofibrils is also suggested.

Protein Synthesis in the Myocardiopathy and Muscular Dystrophy of the Syrian Hamster

“…Watts & Reid (1969) reported that dystrophy in the mouse does not result from any general defect in the protein-synthesizing system and the increase in protein-synthesizing ability of dystrophic muscle was attributed to a decrease in cell size and, concomitantly, wet weight. In this study, however, the rate of incorporation of isotopic amino acids was expressed in terms of the muscle protein content, and the increase reported represents a real increment.…”

The expression of glycogen phosphorylase in normal and dystrophic muscle

“…Both the initial rate and the extent of amino acid incorporation were higher in cell-free systems containing polyribosomes isolated from dystrophic muscles (Srivastava, 1969;Nwagwu, 1975). Differences in the protein-synthetic capacity between normal and dystrophic muscle were abolished when the extent of incorporation was normalized to the precursor amino acid pool size (Watts & Reid, 1969;Kitchen & Watts, 1973), although the initial rate of amino acid incorporation into both total and soluble protein pools was much faster in dystrophic (129dYldY) mice.…”

Protein synthesis in chicken muscular dystrophy

“…From the data now available, it must be concluded that the muscular dystrophies of chickens, mice, and men differ substantially at the molecular level; it is possible that the muscular dystrophies, although pathologically similar, may result from different molecular lesions. Alterations in protein synthetic activity have been identified in chicken and human dystrophic muscle (this report; Weinstock et al 1969;Ionasescu et a!., 1971), but the most reliable data on mouse dystrophy suggest that there is no change in the rate of protein synthesis in dystrophic mouse muscle as compared to normal (Watts and Reid, 1969). Furthermore, the increased protein synthetic activity observed with ribosomes from human dystrophic muscle seems associated with increased collagen synthesis (Ionasescu et al, 1971); we have shown that the increased activity of dystrophic chicken muscle ribosomes was not associated with collagen synthesis.…”