Department of Applied Biological Science, Tokyo Noko university, Saiwai-cho 3-5-8, Fuchu, Tokyo, 183-8509, Japan,
Cytotechnology. 2003 Nov;43(1-3):97-103. doi: 10.1023/b:cyto.0000039898.44839.90.
Effects of leucine and related compounds on protein synthesis were studied in L6 myotubes. The incorporation of [(3)H]tyrosine into cellular protein was measured as an index of protein synthesis. In leucine-depleted L6 myotubes, leucine and its keto acid, alpha-ketoisocaproic acid (KIC), stimulated protein synthesis, while D-leucine did not. Mepacrine, an inhibitor of both phospholipases A(2) and C, canceled stimulatory actions of L-leucine and KIC on protein synthesis. Neither indomethacin, an inhibitor of cyclooxygenase, nor caffeic acid, an inhibitor of lipoxygenase, diminished their stimulatory actions, suggesting no involvement of arachidonic acid metabolism. Conversely, 1-O-hexadecyl-2-O-methylglycerol, an inhibitor of proteinkinase C, significantly canceled the stimulatory actions of L-leucine and KIC on protein synthesis, suggesting an involvement of phosphatidylinositol degradation and activation of protein kinase C. L-Leucine caused a rapid activation of protein kinase C in both cytosol and membrane fractions of the cells. These results strongly suggest that both L-leucine and KIC stimulate protein synthesis in L6 myotubes through activation of phospholipase C and protein kinase C.
亮氨酸及其相关化合物对蛋白质合成的影响在 L6 肌管中进行了研究。将 [(3)H]酪氨酸掺入细胞蛋白作为蛋白质合成的指标进行测量。在亮氨酸耗尽的 L6 肌管中，亮氨酸及其酮酸，α-酮异己酸（KIC），刺激蛋白质合成，而 D-亮氨酸则没有。甲哌氯丙嗪，一种同时抑制磷脂酶 A(2)和 C 的抑制剂，取消了 L-亮氨酸和 KIC 对蛋白质合成的刺激作用。环氧化酶抑制剂吲哚美辛和脂氧合酶抑制剂咖啡酸均未减弱其刺激作用，表明花生四烯酸代谢无参与。相反，1-O-十六烷基-2-O-甲基甘油，一种蛋白激酶 C 的抑制剂，显著取消了 L-亮氨酸和 KIC 对蛋白质合成的刺激作用，表明涉及磷脂酰肌醇的降解和蛋白激酶 C 的激活。L-亮氨酸迅速激活细胞溶质和细胞膜部分的蛋白激酶 C。这些结果强烈表明，L-亮氨酸和 KIC 通过激活磷脂酶 C 和蛋白激酶 C 刺激 L6 肌管中的蛋白质合成。
