Zabłocki K, Bryła J
Institute of Biochemistry, University of Warsaw, Poland.
FEBS Lett. 1989 Dec 18;259(1):144-8. doi: 10.1016/0014-5793(89)81514-5.
In kidney cortex tubules isolated from fed rabbits L-alanine is not utilized as glucose precursor, when added as a sole substrate. However, this amino acid decreases gluconeogenesis from low (up to 1 mM) 2-oxoglutarate concentrations and stimulates this process at higher (2.5-10 mM) ketoacid contents in the suspension medium. Aminooxyacetate, an inhibitor of aminotransferases, abolishes both inhibitory and stimulatory effects of L-alanine on glucose formation. The addition of 2-oxoglutarate increases the incorporation of L-[U-14C]alanine to glucose from 8- to 123-fold, depending upon the ketoacid and alanine concentrations used. In contrast, nonlabelled L-alanine decreases the incorporation of low [U-14C)2-oxoglutarate concentrations into glucose, while it does not affect contribution of 5 mM ketoacid to gluconeogenesis. The data indicate that (i) in the presence of 2-oxoglutarate L-alanine is utilized as glucose precursor in rabbit renal tubules and (ii) this amino acid may decrease the contribution of low extracellular concentrations of the ketoacid to gluconeogenesis.
在从喂食后的兔子分离出的肾皮质小管中，当单独添加L-丙氨酸作为底物时，它不会被用作葡萄糖前体。然而，这种氨基酸在悬浮培养基中低浓度（高达1 mM）的2-氧代戊二酸时会降低糖异生作用，而在较高浓度（2.5 - 10 mM）的酮酸时会刺激这一过程。氨基氧乙酸，一种转氨酶抑制剂，消除了L-丙氨酸对葡萄糖生成的抑制和刺激作用。添加2-氧代戊二酸会使L-[U-¹⁴C]丙氨酸掺入葡萄糖的量增加8至123倍，这取决于所使用的酮酸和丙氨酸浓度。相反，未标记的L-丙氨酸会降低低浓度[U-¹⁴C]2-氧代戊二酸掺入葡萄糖的量，而它不影响5 mM酮酸对糖异生作用的贡献。数据表明：（i）在2-氧代戊二酸存在的情况下，L-丙氨酸在兔肾小管中被用作葡萄糖前体；（ii）这种氨基酸可能会降低细胞外低浓度酮酸对糖异生作用的贡献。
