Hasselgren P O, Hall-Angerås M, Angerås U, Benson D, James J H, Fischer J E
Department of Surgery, University of Cincinnati Medical Center, OH 45267.
Biochem J. 1990 Apr 1;267(1):37-44. doi: 10.1042/bj2670037.
The present study characterized total and myofibrillar protein breakdown rates in a muscle preparation frequently used in vitro, i.e. incubated extensor digitorum longus (EDL) and soleus (SOL) muscles of young rats. Total and myofibrillar protein breakdown rates were assessed by determining net production by the incubated muscles of tyrosine and 3-methylhistidine (3-MH) respectively. Both amino acids were determined by h.p.l.c. Both total and myofibrillar protein breakdown rates were higher in SOL than in EDL muscles and were decreased by incubating the muscles maintained at resting length, rather than flaccid. After fasting for 72 h, total protein breakdown (i.e. tyrosine release) was increased by 73% and 138% in EDL muscles incubated flaccid and at resting length respectively. Net production of tyrosine by SOL muscle was not significantly altered by fasting. In contrast, myofibrillar protein degradation (i.e. 3-MH release) was markedly increased by fasting in both muscles. When tissue was incubated in the presence of 1 munit of insulin/ml, total protein breakdown rate was inhibited by 17-20%, and the response to the hormone was similar in muscles incubated flaccid or at resting length. In contrast, myofibrillar protein breakdown rate was not altered by insulin in any of the muscle preparations. The results support the concepts of individual regulation of myofibrillar and non-myofibrillar proteins and of different effects of various conditions on protein breakdown in different types of skeletal muscle. Thus determination of both tyrosine and 3-MH production in red and white muscle is important for a more complete understanding of protein regulation in skeletal muscle.
本研究对体外常用的一种肌肉制剂（即幼鼠的孵育伸趾长肌（EDL）和比目鱼肌（SOL））中的总蛋白和肌原纤维蛋白分解率进行了表征。通过分别测定孵育肌肉中酪氨酸和3-甲基组氨酸（3-MH）的净生成量来评估总蛋白和肌原纤维蛋白分解率。两种氨基酸均通过高效液相色谱法测定。SOL肌肉中的总蛋白和肌原纤维蛋白分解率均高于EDL肌肉，并且通过将肌肉保持在静息长度而非松弛状态下孵育，分解率会降低。禁食72小时后，松弛状态下孵育的EDL肌肉和静息长度下孵育的EDL肌肉中的总蛋白分解（即酪氨酸释放）分别增加了73%和138%。禁食对SOL肌肉中酪氨酸的净生成量没有显著影响。相反，禁食使两种肌肉中的肌原纤维蛋白降解（即3-MH释放）显著增加。当组织在每毫升含有1个胰岛素单位的条件下孵育时，总蛋白分解率受到17%-20%的抑制，并且在松弛或静息长度下孵育的肌肉中对该激素的反应相似。相比之下，胰岛素对任何一种肌肉制剂中的肌原纤维蛋白分解率均无影响。这些结果支持了肌原纤维蛋白和非肌原纤维蛋白的个体调节概念，以及各种条件对不同类型骨骼肌中蛋白分解的不同影响。因此，测定红肌和白肌中酪氨酸和3-MH的生成量对于更全面地了解骨骼肌中的蛋白质调节非常重要。
