- Protein synthesis was studied in contracting muscles of the perfused rat hindlimb, in skeletal muscles from diabetic rats, in livers from rats deprived of food and in livers perfused with media deficient in methionine or tryptophan. Rates of protein synthesis were markedly inhibited in response to muscle contractions in tibialis anterior, gastrocnemius and plantaris muscles, but were unaffected in soleus. Rates of synthesis returned toward those observed in the resting condition during the recovery period following contractile activity. The changes in protein synthetic rates were positively correlated with tissue contents of ATP, ATP/ADP ratio, creatine phosphate, and inversely proportional to tissue lactate concentration. Protein synthesis was preferentially inhibited at the initiation step of translation by amino acid deprivation in perfused livers, in livers of rats deprived of food for 24 hr, and in diabetic skeletal muscles. The goal was to determine whether the tRNA(,i)('met) was rate-limiting for protein synthesis. The extent to which tRNA(,i)('met) esterified to methionine was not altered by any of the physiological conditions imposed in either muscle or liver. Approximately 80, 70 and 65 percent of tRNA(,i)('met) was aminoacylated in unperfused livers from either fed or starved rats, livers perfused with either supplemented or amino acid deficient media and hindlimb muscles from either diabetic or control rats, respectively. Based on a cellular concentration of 2 (mu)M for total tRNA(,i)('met), the concentration of uncharged and charged tRNA(,i)('met) was 0.7 (mu)M and 1.3 (mu)M, respectively. The methionyl-tRNA synthetase is a non-equilibrium reaction based on an estimate of the mass-action ratio of 0.012 in control livers, and therefore, may be a flux-generating step in the initiation pathway. The cellular concentration of binary complex eIF-2(.)GTP is estimated at 0.10 (mu)M which is 10-fold less than met-tRNA(,i) concentration. Therefore, a 80 to 90% decrease in tRNA(,i)('met) charging would be necessary to diminish ternary complex formation.
- Dissertation Note:
- Ph.D. The Pennsylvania State University 1985.
- Source: Dissertation Abstracts International, Volume: 46-06, Section: B, page: 1835.
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