Malaisse W J, Sener A, Carpinelli A R, Anjaneyulu K, Lebrun P, Herchuelz A, Christophe J
Mol Cell Endocrinol. 1980 Nov;20(2):171-89. doi: 10.1016/0303-7207(80)90080-5.
Exogenous L-glutamine is actively metabolized in rat pancreatic islets. The rate of L-glutamine deamidation largely exceeds the rate of glutamate conversion to gamma-aminobutyrate and alpha-ketoglutarate. The latter conversion occurs in part by oxidative deamination, and in part by transamination reactions coupled with the conversion of 2-keto acids (pyruvate, oxaloacetate), themselves derived from the metabolism of glutamine, to their corresponding amino acids (alanine, aspartate). An important fraction of malate formed from alpha-ketoglutarate leaves the Krebs cycle and is converted to pyruvate, the process being apparently associated with the induction of a more reduced state in cytosolic redox couples. L-Glutamine abolishes the oxidation of endogenous nutrients is documented by the fact that the glutamine-induced increase in O2 consumption is much lower than expected from the rate of 14CO2 output from islets exposed to L-[U-14C]glutamine, L-Glutamine, although decreasing K+ conductance, fails to stimulate insulin release both in the absence and presence of D-glucose. It is proposed that L-glutamine represents a major fuel for pancreatic islets under physiological conditions.
外源性L-谷氨酰胺在大鼠胰岛中被积极代谢。L-谷氨酰胺脱酰胺的速率大大超过谷氨酸转化为γ-氨基丁酸和α-酮戊二酸的速率。后者的转化部分通过氧化脱氨发生，部分通过转氨反应与2-酮酸（丙酮酸、草酰乙酸）的转化偶联，这些2-酮酸本身源自谷氨酰胺的代谢，转化为它们相应的氨基酸（丙氨酸、天冬氨酸）。由α-酮戊二酸形成的苹果酸的一大部分离开三羧酸循环并转化为丙酮酸，该过程显然与细胞溶质氧化还原对中更还原状态的诱导有关。L-谷氨酰胺消除内源性营养物质的氧化这一点由以下事实证明：谷氨酰胺诱导的氧气消耗增加远低于暴露于L-[U-14C]谷氨酰胺的胰岛中14CO2输出速率所预期的值，L-谷氨酰胺虽然降低钾离子电导，但在不存在和存在D-葡萄糖的情况下均未能刺激胰岛素释放。有人提出，在生理条件下，L-谷氨酰胺是胰岛的主要燃料。
