Effect of nutrition on protein turnover in skeletal muscle
Millward, D.J.; Waterlow, J.C.
Federation Proceedings 37(9): 2283-2290
1978
ISSN/ISBN: 0014-9446 PMID: 350634 Document Number: 132961
The effects of nutrition on the developmental changes in muscle protein turnover were studied in relation to the growth of the size and number of DNA-units in muscle. The developmental fall in the fractional synthesis rate is estimated by the increase in DNA-unit size and the way in which the synthesis rate per DNA-unit, expressed as protein in g/g DNA daily, varies during development. Malnutrition reduces the rate of production and the total number of DNA-units. The synthesis rate per DNA-unit is only affected in malnourished rats, and not in well-fed rats. Ultimate DNA-unit size is not affected by malnutrition but is related to the function of the muscle and the protein breakdown rate. This may be determined by function. As rates of synthesis per DNA-unit are similar in different muscles, DNA-unit size may be regulated by the fractional rate of protein breakdown (FBR). The way in which the FBR varies with the growth rate seems to be affected by strain differences as well as nutrition. Treatments that stop growth entirely depress both the fractional rate of protein synthesis (FSR) and the FBR to varying degrees according to the severity and duration of the treatment. The FSR falls as a result of decreases in ribosome number and activity, and in addition the relative synthesis rates of protein fractions alter. Protein breakdown does not exhibit acute increases, rising after prolonged starvation only. While the nature of the changes in breakdown is unclear, changes in protein synthesis seem to reflect the hormonal response to the nutritional state rather than substrate supply.