Fern E B, Waterlow J C
Experientia Suppl. 1983;44:89-106. doi: 10.1007/978-3-0348-6540-1_7.
Not many studies have been done on protein turnover during recovery from malnutrition. Some relevant information can, however, be obtained from measurements on normal growing animals, since rehabilitation and normal growth have in common a rapid rate of net protein synthesis. The key question is the extent to which net gain in protein results from an increase in synthesis or a decrease in breakdown or both. Different studies have used different methods, and all methods for measuring protein turnover have some disadvantages and sources of error. It is important to bear this in mind in evaluating the results. Consequently, part of this paper will be devoted to questions of methodology. Whole body protein turnover has been measured in children recovering from severe malnutrition. During the phase of rapid catch-up growth the rate of protein synthesis is increased. As might be expected, it increases linearly with the rate of weight gain. At the same time there is a smaller increase in the rate of protein breakdown. The resultant of these two processes is that, over and above the basal rate of protein synthesis, 1.4 grams of protein have to be synthesized for 1 gram to be laid down. Very similar results have been obtained in rapidly growing young pigs. Experimental studies on muscle growth in general confirm the conclusion that, at least in muscle, rapid growth is associated with rapid rates of protein breakdown as well as of synthesis. This has been shown in muscles of young growing rats, as well as in muscles in which hypertrophy has been induced by stretch or other stimuli. In contrast, the evidence suggests that rapid growth involves a fall in the rate of protein degradation. The magnitude of the nitrogen balance under any conditions is determined by the difference between synthesis and breakdown. In the absence of any storage of amino acids, this must be the same as the difference between intake and excretion (S - B = I - E). A question of great interest is whether, at a given intake, the extent of N balance is determined primarily by regulation of synthesis and breakdown or by regulation of amino acid oxidation. Clearly, a reduction in amino acid degradation is equivalent to an increase in amino acid intake. An interesting subject for future research is the extent to which the amino acid degrading enzymes adapt to the requirements imposed by growth and rehabilitation.
关于营养不良恢复过程中的蛋白质周转，所做的研究并不多。不过，一些相关信息可以从对正常生长动物的测量中获得，因为康复和正常生长都有快速的净蛋白质合成速率这一共同点。关键问题是蛋白质净增加在多大程度上是由合成增加、分解减少或两者共同作用导致的。不同的研究使用了不同的方法，而且所有测量蛋白质周转的方法都有一些缺点和误差来源。在评估结果时牢记这一点很重要。因此，本文的一部分将专门讨论方法学问题。已经对从严重营养不良中恢复的儿童进行了全身蛋白质周转的测量。在快速追赶生长阶段，蛋白质合成速率增加。正如预期的那样，它与体重增加速率呈线性增加。同时，蛋白质分解速率的增加幅度较小。这两个过程的结果是，除了蛋白质合成的基础速率外，每沉积1克蛋白质必须额外合成1.4克蛋白质。在快速生长的幼猪中也得到了非常相似的结果。一般来说，关于肌肉生长的实验研究证实了这样的结论，即至少在肌肉中，快速生长与蛋白质分解以及合成的快速速率相关。这已在幼年生长大鼠的肌肉中以及通过拉伸或其他刺激诱导肥大的肌肉中得到证明。相比之下，有证据表明快速生长涉及蛋白质降解速率的下降。在任何条件下，氮平衡的大小由合成与分解之间的差异决定。在没有氨基酸储存的情况下，这必须与摄入和排泄之间的差异相同（S - B = I - E）。一个非常有趣的问题是，在给定摄入量的情况下，氮平衡的程度主要是由合成和分解的调节还是由氨基酸氧化的调节决定的。显然，氨基酸降解的减少等同于氨基酸摄入量的增加。一个未来研究的有趣课题是氨基酸降解酶在多大程度上适应生长和康复所带来的需求。
