The proteasome inhibitors are used as research tools to study of the ATP-dependent ubiquitin-proteasome system. Some of them are at present undergoing clinical trials to be used as therapeutic agents for cancer or inflammation. These diseases are often accompanied by muscle wasting. We herein demonstrate findings about new proteasome inhibitors, belactosin A and C, and their direct effect on protein metabolism in rat skeletal muscle. M. soleus (SOL) and m. extensor digitorum longus (EDL) were dissected from both legs of male rats (40–60g) and incubated in a buffer containing belactosin A or C (30 μM) or no inhibitor. The release of amino acids into the medium was estimated using high performance liquid chromatography to calculate total and myofibrillar proteolysis. Chymotrypsin-like activity (CTLA) of proteasome and cathepsin B, L activity were determined by fluorometric assay. Protein synthesis and leucine oxidation were detected using specific activity of L-[1-¹⁴C] leucine added to medium. Inhibited and control muscles from the same rat were compared using paired t-test. The results indicate that after incubation with both belactosin A and C total proteolysis and CTLA of proteasome decreased while cathepsin B, L activity did not change in both SOL and EDL. Leucine oxidation was significantly enhanced in SOL, protein synthesis decreased in EDL. Myofibrillar proteolysis was reduced in both muscles in the presence of belactosin A only. In summary, belactosin A and C affected basic parameters of protein metabolism in rat skeletal muscle. The response was both muscle- and belactosin-type-dependent.

中文翻译：

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新的蛋白酶体抑制剂，belactosin A 和 C，对离体大鼠骨骼肌蛋白质代谢的影响。

蛋白酶体抑制剂被用作研究工具来研究依赖于 ATP 的泛素-蛋白酶体系统。其中一些目前正在进行临床试验，以用作癌症或炎症的治疗剂。这些疾病通常伴随着肌肉萎缩。我们在此展示了关于新蛋白酶体抑制剂、belactosin A 和 C 的发现，以及它们对大鼠骨骼肌蛋白质代谢的直接影响。M. 比目鱼 (SOL) 和 m。从雄性大鼠（40-60g）的双腿切下趾长伸肌（EDL），并在含有 belactosin A 或 C（30 μM）或不含抑制剂的缓冲液中孵育。使用高效液相色谱法来估计氨基酸释放到培养基中以计算总蛋白水解和肌原纤维蛋白水解。蛋白酶体和组织蛋白酶 B 的糜蛋白酶样活性 (CTLA)，L活性通过荧光测定法测定。使用 L-[1-¹⁴ C] 亮氨酸添加到培养基中。使用配对 t 检验比较来自同一只大鼠的抑制肌肉和对照肌肉。结果表明，与belactosin A 和C 孵育后，蛋白酶体的总蛋白水解和CTLA 降低，而组织蛋白酶B、L 活性在SOL 和EDL 中均未发生变化。SOL中亮氨酸氧化显着增强，EDL中蛋白质合成减少。仅在 belactosin A 存在的情况下，两块肌肉中的肌原纤维蛋白水解均减少。总之，belactosin A 和 C 影响大鼠骨骼肌蛋白质代谢的基本参数。反应是肌肉和 belactosin 类型依赖。