Studies on the regulation of tissue protein sythesis in chickens given various nutrients

测定了不同营养条件下雏鸡肝脏和肌肉中蛋白质合成速率和mRNA水平。用大剂量L-[4-_3H]苯丙氨酸注射法测定蛋白质合成分数（FSR）。用poly（U）-Sepharose 4 B亲和层析法提取Poly（A）+RNA作为mRNA，研究了不同蛋白质水平（0 ~ 60%）的影响。肝脏和肌肉蛋白质的FSR随日粮蛋白质水平从0增加到20%（蛋白质需要量）而增加，而当日粮蛋白质水平从20%增加到40%时，这两个速率都显著下降。肝脏FSR的变化由RNA浓度（RAN：蛋白质比率）和肝脏mRNA含量的变化来解释。肌肉FSR对低于需要量的蛋白质水平的反应部分受RNA合成蛋白质效率变化的调节，而高于需要量的反应不仅受RNA效率的调节，而且受RNA：mRNA比例的调节（相对于mRNA的核糖体数量），mRNA：DNA比率（mRNA利用率）和DNA：蛋白质比值（DNA浓度）。其次，测定了强饲后再饲雏鸡肝脏和肌肉蛋白质合成及mRNA含量的时程变化。再次投喂后30 min，肝脏和肌肉的FSR显著高于未投喂组。第三，在禁食2 d后，对含蛋白质、碳水化合物和脂肪的试验日粮进行强制投喂，未观察到肝脏FSR的变化。但肌肉FSR在各营养素摄入后0.5h恢复到对照水平。肌肉蛋白质合成的增加可以用RNA合成蛋白质的效率的变化来解释。

The protein synthesis rate and mRNA levels were measured in the liver and muscle of chicks under various nutritional conditions. Fractional synthesis rate (FSR) of protein was measured using a large dose injection of L-[4-_3H] phenylalanine. Poly (A)+RNA was extracted as mRNA using poly (U)-Sepharose 4B affinity chromatograpy.The influence of varying dietary protein levels (0 to 60%) was examined. The FSRs of both liver and muscle protein incereased with increasing dietary protein levels from 0 to 20% (the protein requirement), whereas when dietary protein increased from 20 to 40%, both rates decreased significantly. The change in liver FSR was accounted for by changes in RNA concentration (RAN : protein ratio) and hepatic mRNA content. The response of muscle FSR to varying dietary protein levels below the requirement is partially regulated by the change in the efficiency of RNA in synthesizing protein, whereas above the requirement by not only the efficiency of RNA but also RNA : mRNA ratio (ribosome number relative to mRNA), mRNA : DNA ratio (mRNA availability) and DNA : protein ratio (DNA concentration).Secondly, the time course changes in liver and muscle protein synthesis and mRNA contents were measured in force-fed chicks followed by refeeding. Liver and muscle FSRs were significantly greater 30 min after refeeding compared to that of unfed chicks.Thirdly, experimental diets containing individual nutrients (protein, carbohydrate, lipid) were force-fed to chicks after 2 d food-deprivation, and no changes in liver FSR were observed. However, muscle FSR returned to the control level 0.5h after consumption of each nutrient. The increase in muscle protein synthesis was explained by the change in the efficiency of RNA in synthesizing protein.