Millward D J, Garlick P J, Stewart R J, Nnanyelugo D O, Waterlow J C
Biochem J. 1975 Aug;150(2):235-43. doi: 10.1042/bj1500235.
Because of turnover, protein synthesis and breakdown can each be involved in the regulation of the growth of tissue protein. To investigate the regulation of skeletal-muscle-protein growth we measured rates of protein synthesis and breakdown in growing rats during development on a good diet, during development on a marginally low-protein diet and during rehabilitation on a good diet after a period of severe protein deficiency. Rates of protein synthesis were measured in vivo with a constant intravenous infusion of [14C]tyrosine. The growth rate of muscle protein was measured and the rate of breakdown calculated as breakdown rate=synthesis rate-growth rate. These measurements showed that during development on a good diet there was a fall with age in the rate of protein synthesis resulting from a fall in capacity (RNA concentration) and activity (synthesis rate per unit of RNA). There was a fall with age in the breakdown rate so that the rate was highest in the weaning rats, with a half-life of 3 days. There was a direct correlation between the fractional growth and breakdown rates. During rehabilitation on the good diet, rapid growth was also accompanied by high rates of protein breakdown. During growth on the inadequate diet protein synthesis rates were lesss than in controls, but growth occurred because of decreased rates of protein breakdown. This compression was not complete, however, since ultimate muscle size was only one-half that of controls. It is suggested that increased rates of protein breakdown are a necessary accompaniment to muscle growth and may result from the way in which myofibrils proliferate.
由于蛋白质周转，蛋白质合成与分解均可能参与组织蛋白生长的调节。为了研究骨骼肌蛋白生长的调节机制，我们测定了生长大鼠在以下三个阶段的蛋白质合成与分解速率：正常饮食发育阶段、轻度低蛋白饮食发育阶段以及严重蛋白质缺乏一段时间后恢复正常饮食阶段。通过持续静脉输注[14C]酪氨酸在体内测定蛋白质合成速率。测定肌肉蛋白的生长速率，并将分解速率计算为：分解速率 = 合成速率 - 生长速率。这些测量结果表明，在正常饮食发育阶段，由于能力（RNA浓度）和活性（每单位RNA的合成速率）下降，蛋白质合成速率随年龄增长而降低。分解速率也随年龄下降，因此断奶大鼠的分解速率最高，半衰期为3天。生长分数与分解速率之间存在直接相关性。在恢复正常饮食阶段，快速生长也伴随着高蛋白分解速率。在低蛋白饮食生长阶段，蛋白质合成速率低于对照组，但由于蛋白质分解速率降低仍有生长。然而，这种压缩并不完全，因为最终肌肉大小仅为对照组的一半。有人提出，高蛋白分解速率是肌肉生长的必要伴随现象，可能是由肌原纤维增殖的方式导致的。
