Wu G Y, Thompson J R, Baracos V E
Department of Animal Science, University of Alberta, Edmonton, Canada.
Biochem J. 1991 Mar 15;274 ( Pt 3)(Pt 3):769-74. doi: 10.1042/bj2740769.
Oxidative decarboxylation of L-[1-14C]glutamine was studied in isolated chick and rat skeletal muscles incubated in the presence of glucose, insulin and plasma concentrations of amino acids. (1) The rate of oxidative decarboxylation of L-[1-14C]glutamine was high, and exceeded that of L-[1-14C]leucine in all muscles. (2) The rate of oxidative decarboxylation of L-[1-14C]glutamine increased with increasing intracellular concentrations of glutamine. (3) The activities of glutamine aminotransferases K and L were more than 10-fold greater in rat than in chick skeletal muscles. (4) Mitochondrial phosphate-activated glutaminase activity was approx. 10-fold greater in chick than in rat skeletal muscles and increased with increasing glutamine concentrations. (5) An inhibitor of glutaminase, 6-diazo-5-oxo-L-norleucine, inhibited the rate of glutamine decarboxylation in chick, but not in rat, skeletal muscle. These findings suggest that glutamine degradation in skeletal muscle may be substantial and may make an important contribution to the regulation of intramuscular glutamine concentrations. A species difference in the pathways and the subcellular location for the conversion of glutamine into 2-oxoglutarate in rat and chick skeletal muscles is implied by the relative activities of glutamine-degrading enzymes.
在存在葡萄糖、胰岛素和血浆氨基酸浓度的条件下，对分离的鸡和大鼠骨骼肌中L-[1-¹⁴C]谷氨酰胺的氧化脱羧作用进行了研究。（1）L-[1-¹⁴C]谷氨酰胺的氧化脱羧速率很高，且在所有肌肉中均超过L-[1-¹⁴C]亮氨酸的氧化脱羧速率。（2）L-[1-¹⁴C]谷氨酰胺的氧化脱羧速率随细胞内谷氨酰胺浓度的增加而增加。（3）大鼠骨骼肌中谷氨酰胺转氨酶K和L的活性比鸡骨骼肌中的活性高10倍以上。（4）鸡骨骼肌中线粒体磷酸激活的谷氨酰胺酶活性比大鼠骨骼肌中的活性高约10倍，且随谷氨酰胺浓度的增加而增加。（5）谷氨酰胺酶抑制剂6-重氮-5-氧代-L-正亮氨酸抑制鸡骨骼肌中谷氨酰胺的脱羧速率，但不抑制大鼠骨骼肌中的脱羧速率。这些发现表明，骨骼肌中谷氨酰胺的降解可能相当可观，并且可能对肌肉内谷氨酰胺浓度的调节做出重要贡献。谷氨酰胺降解酶的相对活性暗示了大鼠和鸡骨骼肌中谷氨酰胺转化为2-氧代戊二酸的途径和亚细胞定位存在种属差异。
