Protein synthesis in muscles from normal and dystrophic hamsters

Ribosomal protein synthesis in cultured skin fibroblast cells obtained from patients with Duchenne muscular dystrophy

Ribosomes and ribosomal subunits were extracted from cultured skin fibroblasts from patients with Duchenne muscular dystrophy (DMD). A poly(U)-directed polyphenylalanine synthesis system was used to test 80S ribosomes from DMD cells and normal controls as well as hybrid 80S couples of subunits from DMD cells and control cells. The activity of ribosomes extracted from the patients was 38-62% lower than that of normal controls. Of the 80S hybrid ribosomes, only those consisting of 40S subunits from DMD cells and 60S subunits from the control cells, showed a similar decrease in activity. That means that the defect is exclusively based on an alteration in the small ribosomal subunit.

Phosphorylation of the sarcolemma of dystrophic and normal hamster muscle following denervation

The rapid phosphorylation at 0 degree C of sarcolemma preparations of hamster leg muscle was compared with (Na+,K+)-ATPase activity in sham-operated and 7-day denervated muscle. The phosphorylation appeared to be under the trophic influence of the sciatic nerve since the denervated preparations exhibited a markedly reduced phosphorylation. In similar studies using dystrophic hamsters the sarcolemma preparations from sham-operated and denervated leg muscle both exhibited the same degree of phosphorylation.

Increase in the amount of elongation factor 2 in chicken muscular dystrophy

The amount of elongation factor 2 (EF2) in the cytoplasm and ribosome of breast muscle cell from normal and dystrophic strains of chicken was measured. Concentration in the cytoplasm of 20-day-old embryonic dystrophic muscle was higher than that in normal muscle, but no difference in content was found in muscles of 15-day-old embryos. The amount of EF2 bound to ribosomes was identical in normal and dystrophic muscles during all stages of development. Peptide mapping patterns of partial proteolytic fragments of EF2 from normal and dystrophic chicken breast muscles were similar. The increase in cytoplasmic protein synthetic activity of dystrophic breast muscles reported previously seems to be due to the corresponding increase in the number of EF2 molecules rather than to their modification in dystrophic muscle.

Pre- and post-natal growth and protein turnover in smooth muscle, heart and slow- and fast-twitch skeletal muscles of the rat

The growth of one smooth and three individual striated muscles was studied from birth to old age (105 weeks), and where possible during the later stages of foetal life also. Developmental changes in protein turnover (measured in vivo) were related to the changing patterns of growth within each muscle, and the body as a whole. Developmental growth (i.e. protein accumulation) in all muscles involved an increasing proportion of protein per unit wet weight, as well as cellular hypertrophy. The contribution of the heart towards whole-body protein and nucleic acid contents progressively decreased from 18 days of gestation to senility. In contrast, post-natal changes in both slow-twitch (soleus) and fast-twitch (tibialis anterior) skeletal muscles remained reasonably constant with respect to whole-body values. Such age-related growth in all four muscle types was accompanied by a progressive decline in both the fractional rates of protein synthesis and breakdown, the changes in synthesis being more pronounced. Age for age, the fractional rates of synthesis were highest in the oesophageal smooth muscle, similar in both cardiac and the slow-twitch muscles, and lowest in the fast-twitch tibialis muscle. Despite these differences, the developmental fall in synthetic rates was remarkably similar in all four muscles, e.g. the rates at 105 weeks were 30-35% of their values at weaning. Such developmental changes in synthesis were largely related to diminishing ribosomal capacities within each muscle. When measured under near-steady-state conditions (i.e. 105 weeks of age), the half-lives of mixed muscle proteins were 5.1, 10.4, 12.1 and 18.3 days for the smooth, cardiac, soleus and tibialis muscles respectively. Old-age atrophy was evident in the senile animals, this being more marked in each of the four muscle types than in the animal as a whole. In each muscle of the senile rats the protein content and composition per unit wet weight, and both the fractional and total rates of synthesis, were significantly lower than in the muscles of younger, mature, animals (i.e. 44 weeks). In the soleus the decreased synthesis rate appeared to be related to a further fall in the ribosomal capacity. In contrast, the changes in synthesis in the three remaining muscles correlated with significant decreases in the synthetic rate per ribosome.(ABSTRACT TRUNCATED AT 400 WORDS)

The purification and characterization of an inhibitor of protein synthesis from the muscle of dystrophic mice and homozygous control mice

Homogenates of hindlimb muscle were obtained from homozygous (+/+) control mice and dystrophic (dy/dy) mice of the ReJ 129 strain and subjected to purification by ion exchange chromatography, gel filtration, centrifugation on sucrose gradients, and sodium dodecyl sulphate gel electrophoresis. A proteinaceous material inhibitory to protein synthesis that was detected previously in fractions from dystrophic muscle (Petryshyn and Nicholls 1978) was present at reduced levels of activity in muscle fractions from homozygous controls. Although the specific activity after the sucrose gradient step was similar in the 2 groups of animals, the activity per animal was 3 times higher in the dystrophic mice. Evidence is presented to support the view that the inhibitory material is identical in the 2 groups and also that the active protein, of an approximate molecular weight of 120000, can be denatured by heat and 2-mercaptoethanol to the less active form that was described previously, of an approximate molecular weight of 70000.

Incorporation of amino acids into soluble and membrane protein fractions of dystrophic hamsters

The incorporation of labelled leucine was measured in protein fractions of muscle in intact control and dystrophic female hamsters and also in cell-free preparations obtained from these animals. The labelling of the soluble sarcoplasmic protein fraction, the microsomal protein fraction and the sarcolemma protein fraction was increased in the dystrophic hindleg muscle. The specific radioactivities of the sarcolemma protein fraction and other fractions were increased markedly relative to that of free leucine in the dystrophic muscle. In cell-free preparations where ribonuclease effects were avoided, the dystrophic muscle exhibited an increased synthesis of peptide bonds.