Lajtha A, Toth J, Fujimoto K, Agrawal H C
Biochem J. 1977 May 15;164(2):323-9. doi: 10.1042/bj1640323.
The incorporation of tyrosine into proteins was measured after the subcutaneous implantation of a pellet of [14C]tyrosine in mice. This method keeps the specific radioactivity of free tyrosine fairly constant and makes it possible to follow incorporation up to a 10-day period. At the end of 10 days most of the protein-bound tyrosine was replaced (i.e. most protein turned over) in lung, liver, heart, kidney and spleen; about half was replaced in brain, one-quarter in muscle. The rate of protein turnover in myelin was approx. 40% of that of whole brain proteins; at 10 days one-fifth of the myelin proteins were replaced. All protein components of myelin measured were in a dynamic state; incorporation decreased in the following order, Wolfgram greater than DM-20 greater than basic greater than proteolipid proteins. The incorporation of tyrosine into each protein fraction was greater in the 0-5-day than in the 5-10-day period, indicating heterogeneity of metabolic rates. The results show that after myelination at least a portion of each protein component of myelin is undergoing significant metabolic turnover. In the adult, myelin components are not stable, but turnover is heterogeneous, and each protein may be compartmentalized. Turnover can be influenced by a variety of factors.
在小鼠皮下植入含有[14C]酪氨酸的小球后，检测酪氨酸掺入蛋白质的情况。该方法能使游离酪氨酸的比放射性保持相当恒定，并有可能追踪长达10天的掺入情况。在10天结束时，肺、肝、心、肾和脾中大部分与蛋白质结合的酪氨酸被替换（即大部分蛋白质周转）；脑中约一半被替换，肌肉中四分之一被替换。髓鞘中蛋白质周转的速率约为全脑蛋白质的40%；在10天时，五分之一的髓鞘蛋白质被替换。所检测的髓鞘所有蛋白质成分都处于动态状态；掺入量按以下顺序降低，沃尔夫格拉姆蛋白大于DM - 20大于碱性蛋白大于蛋白脂质蛋白。酪氨酸掺入各蛋白质组分在0 - 5天比在5 - 10天期间更多，表明代谢速率存在异质性。结果表明，髓鞘形成后，髓鞘的每个蛋白质组分至少有一部分经历显著的代谢周转。在成体中，髓鞘成分不稳定，但周转是异质性的，且每种蛋白质可能被分隔开来。周转可受多种因素影响。
