Garber A J, Karl I E, Kipnis D M
J Biol Chem. 1976 Feb 10;251(3):836-43.
The synthesis and release of alanine and glutamine have been studied in the intact rat epitrochlaris skeletal muscle preparation. Aspartate, cysteine, leucine, valine, methionine, isoleucine, serine, theronine, and glycine increased significantly the formation and release of alanine from muscle. Cysteine, leucine, valine, methionine, isoleucine, tyrosine, lysine, and phenylalanine increased the rate of glutamine synthesis. Only ornithine, arginine, and tryptophan were without effect on the synthesis of either alanine or glutamine. Half-maximal stimulation of alanine and glutamine formation by added amino acids was observed with concentrations ranging between 0.5 and 1.0 mM. Increases in alanine and glutamine formation were not accompanied by changes in pyruvate production or glucose uptake. The progressive decline in alanine and glutamine synthesis noted on prolonged incubation was prevented by the addition of amino acids to the incubation medium. Stimulation of alanine synthesis by added amino acids was unaffected by inhibition of glycolysis with iodoacetate. Inhibition of alanine aminotransferase with aminooxyacetate significantly decreased alanine formation. Pyruvate and ammonium chloride did not increase further the rate of either alanine or glutamine formation above that produced by added amino acids. These data indicate that most amino acids are precursors for alanine and glutamine synthesis in skeletal muscle. A general mechanism is presented for the de novo formation of alanine from amino acids in skeletal muscle, and the importance of proteolysis for the supply of amino acid precursors for alanine and glutamine synthesis is discussed.
在完整的大鼠肱三头肌骨骼肌标本中，对丙氨酸和谷氨酰胺的合成与释放进行了研究。天冬氨酸、半胱氨酸、亮氨酸、缬氨酸、蛋氨酸、异亮氨酸、丝氨酸、苏氨酸和甘氨酸显著增加了肌肉中丙氨酸的形成与释放。半胱氨酸、亮氨酸、缬氨酸、蛋氨酸、异亮氨酸、酪氨酸、赖氨酸和苯丙氨酸提高了谷氨酰胺的合成速率。只有鸟氨酸、精氨酸和色氨酸对丙氨酸或谷氨酰胺的合成没有影响。添加的氨基酸对丙氨酸和谷氨酰胺形成的半最大刺激浓度范围在0.5至1.0 mM之间。丙氨酸和谷氨酰胺形成的增加并未伴随着丙酮酸生成或葡萄糖摄取的变化。通过向孵育培养基中添加氨基酸，可防止长时间孵育时丙氨酸和谷氨酰胺合成的逐渐下降。添加的氨基酸对丙氨酸合成的刺激不受碘乙酸对糖酵解抑制的影响。用氨基氧乙酸抑制丙氨酸转氨酶可显著降低丙氨酸的形成。丙酮酸和氯化铵在添加氨基酸所产生的速率之上，并未进一步提高丙氨酸或谷氨酰胺的形成速率。这些数据表明，大多数氨基酸是骨骼肌中丙氨酸和谷氨酰胺合成的前体。本文提出了骨骼肌中由氨基酸从头合成丙氨酸的一般机制，并讨论了蛋白水解对丙氨酸和谷氨酰胺合成中氨基酸前体供应的重要性。
