AMINO ACID AND PROTEIN METABOLISM OF THE BRAIN—I
AMINO ACID AND PROTEIN METABOLISM OF THE BRAIN—I
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大脑的氨基酸和蛋白质代谢——I
DOI：
10.1111/j.1471-4159.1957.tb12084.x
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发表时间：
1957
期刊：
影响因子：
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通讯作者：
H. Waelsch
中科院分区：
文献类型：
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作者：
A. Lajtha;S. Furst;A. Gerstein;H. Waelsch
自从Schoenheimer等人（1939）对代谢进行经典研究以来，在双标记L-亮氨酸的研究中，首次估计了肝脏蛋白质的半衰期，借助标记氨基酸，特别是甘氨酸和甲硫氨酸，测定了许多器官蛋白质的周转率（BORSOOK，1950年）。大多数蛋白质周转率的估计是基于相对较长时间的实验结果，其中标记的氨基酸在蛋白质中的出现或从蛋白质中的消失被跟踪。然而，在这样的实验中，将主要测量相对缓慢代谢的蛋白质的平均半衰期;快速代谢的a B o m器官蛋白质的周转率必须根据活性时间曲线的上升部分计算。在长期的实验中，半衰期短的蛋白质会失去部分标记，这些标记会被体内的游离氨基酸稀释。蛋白质周转值的早期测定也受到缺乏测定器官蛋白质来源的游离氨基酸的浓度和同位素含量的方法的阻碍。由于这种情况，周转率的估计必须基于对同位素库的性质和动态的假设，标记蛋白质成分就是从同位素库中提取的。尽管存在这些局限性，但研究清楚地表明，器官或组织（如肝、肾或肠粘膜）的蛋白质周转率相对较高;另一方面，器官（如脑或肌肉）的蛋白质周转率存在疑问或被认为非常低。估计内脏（脾、心脏、肾、肠和睾丸）蛋白的半衰期与肝脏蛋白的半衰期（7天）接近;假设皮肤、肌肉、骨、肺和脑的半衰期等于158天（S m N和RIITENBERG，1944; SPRINSON和RITTENBERG，1949）。在这样的估计中，任何具有快速代谢蛋白质的小器官当然不会决定性地改变慢代谢蛋白质半衰期的平均值。
SINCE the classical study of SCHOENHEIMER and associates (1939) on the metabolism . of doubly-labelled L-leucine, a study which provided the first estimate of the halflife time of liver protein, the turnover rates of the proteins of many organs have been determined with the aid of labelled amino acids, in particular glycine and methionine (BORSOOK, 1950). Most of the estimates of protein turnover were based on the results of experiments of relatively long duration in which the appearance of the labelled amino acid in or the disappearance from the proteins was followed. However, in such experiments the average half-lifetime of mainly the relatively slowly metabolized protein will be measured; the turnover rates of the rapidly m e t a b o m organ proteins would have to be calculated from the ascending portion of activitytime curves. During long-term experiments, proteins with a short half-lifetime lose part of their label, which is diluted out by the free amino acids of the body. The earlier determinations of turnover values of proteins suffered also from the handicap of the lack of methods for the determination of the concentration and isotope content of the free amino acids from which the organ proteins are derived. Owing to this situation, the estimate of turnover rates had to be based on assumptions as to the nature and dynamics of the isotope pool from which the labelled protein constituents were drawn. Despite these limitations, the investigations demonstrated clearly the relatively high turnover rates of the proteins of organs or tissues such as liver, kidney, or intestinal mucosa; on the other hand, the turnover rates of the proteins of organs such as brain or muscle were in doubt or considered very low. The half-lifetimes of the proteins of the internal organs (spleen, heart, kidney, intestine, and testes) were estimated as close to that of liver proteins (7 days); those of skin, muscle, bone, lung, and brain were assumed to equal 158 days ( S m N and RIITENBERG, 1944; SPRINSON and RITTENBERG, 1949). In such an estimate any small organ with rapidly metabolized protein would, of course, not decisively change the average values derived for the half-lifetime of the slowly metabolized proteins.