Pardridge W M, Davidson M B
Biochim Biophys Acta. 1979 Jun 1;585(1):34-42. doi: 10.1016/0304-4165(79)90322-2.
Alanine production by skeletal muscle in tissue culture was studied using an established myogenic line (L6) of rat skeletal muscle cells. Correlation analyses were performed on rates of metabolism of alanine, glucose, lactate and pyruvate over incubation periods up to 96 h. Alanine production did not correlate significantly with glucose utilization (r = 0.24, P less than 0.20). Alanine production, however, did correlate with lactate production (r = 0.72, P less than 0.0005) as well as medium (r = 0.50, P less than 0.025) and intracellular (r = 0.85, P less than 0.0005) pyruvate concentrations. The intercepts of the latter two correlation analyses indicated that when medium or cell pyruvate fell below 0.28 mM or 1 nmol/mg protein, respectively, net alanine consumption occurred. Alanine synthesis also correlated (r = 0.71, P less than 0.0005) with the percent change in the cell mass action ratio for the sum of the alanine and aspartate aminotransferase reactions, i.e., [alanine] [malate]/[aspartate] [lactate]. These results suggest that alanine production is not necessarily linked to the rate of glucose utilization but rater to pyruvate overflow above a critical intracellular level; under conditions of pyruvate overflow, alanine synthesis is driven by the tendency to establish equilibrium between metabolites of the linked amino acid transaminases in skeletal muscle.
利用已建立的大鼠骨骼肌细胞成肌细胞系（L6），研究了组织培养中骨骼肌产生丙氨酸的情况。对长达96小时的孵育期内丙氨酸、葡萄糖、乳酸和丙酮酸的代谢速率进行了相关性分析。丙氨酸的产生与葡萄糖利用无显著相关性（r = 0.24，P < 0.20）。然而，丙氨酸的产生与乳酸的产生（r = 0.72，P < 0.0005）以及培养基（r = 0.50，P < 0.025）和细胞内（r = 0.85，P < 0.0005）丙酮酸浓度相关。后两个相关性分析的截距表明，当培养基或细胞丙酮酸分别降至0.28 mM或1 nmol/mg蛋白质以下时，会发生丙氨酸的净消耗。丙氨酸合成也与丙氨酸和天冬氨酸转氨酶反应总和的细胞质量作用比的变化百分比相关（r = 0.71，P < 0.0005），即[丙氨酸][苹果酸]/[天冬氨酸][乳酸]。这些结果表明，丙氨酸的产生不一定与葡萄糖利用速率相关，而是与丙酮酸在临界细胞内水平以上的溢出速率相关；在丙酮酸溢出的情况下，丙氨酸的合成是由骨骼肌中相关氨基酸转氨酶代谢物之间建立平衡的趋势驱动的。
