Dahlmann B, Kuehn L
Diabetes Forschungsinstitut, Düsseldorf, Germany.
Mol Biol Rep. 1995;21(1):57-62. doi: 10.1007/BF00990972.
Similar to all other eukaryotic cells and tissues muscle tissue contains the proteolytic system of 20S/26S proteasomes with the 20S proteasome existing predominantly in a latent state. Unlike with the mammalian enzyme in vitro transition from the latent to the activated state of the 20S proteasomes isolated from muscle of several fish species and from lobster can be achieved by heat shock. It is very likely that the activated state of the 20S proteasome corresponds to the physiologically active form of the enzyme since only that one is able to attack sarcoplasmic and myofibrillar proteins to any significant extent. As perfusion of rat hindquarters with presumptive low molecular mass activators like free fatty acids does not result in an activation of the muscle proteasome other--possibly protein activators--may serve this purpose in vivo. The 26S proteasome complex may be regarded as such a proteasome/activator complex. The 26S proteasome complex has the ability to degrade protein (-ubiquitin-conjugates) by an ATP-consuming reaction. Since increased amounts of ubiquitinated proteins as well as an enhanced activity of the ATP (-ubiquitin)-dependent proteolytic system have been measured in rat muscle tissue during various catabolic conditions, it is not unlikely that this pathway is responsible for catalysis of muscle protein breakdown.
与所有其他真核细胞和组织相似，肌肉组织含有20S/26S蛋白酶体的蛋白水解系统，其中20S蛋白酶体主要以潜伏状态存在。与哺乳动物酶不同，在体外，从几种鱼类肌肉和龙虾中分离出的20S蛋白酶体从潜伏状态转变为激活状态可通过热休克实现。20S蛋白酶体的激活状态很可能对应于该酶的生理活性形式，因为只有激活状态的蛋白酶体才能在很大程度上攻击肌浆蛋白和肌原纤维蛋白。由于用游离脂肪酸等假定的低分子量激活剂灌注大鼠后肢并不会导致肌肉蛋白酶体的激活，其他物质——可能是蛋白质激活剂——可能在体内起到这一作用。26S蛋白酶体复合物可被视为这样一种蛋白酶体/激活剂复合物。26S蛋白酶体复合物能够通过消耗ATP的反应降解蛋白质（-泛素缀合物）。由于在各种分解代谢条件下，在大鼠肌肉组织中已检测到泛素化蛋白质的量增加以及ATP（-泛素）依赖性蛋白水解系统的活性增强，因此这条途径很可能负责催化肌肉蛋白质的分解。
