Wadoux P, Welbourne T C
Can J Biochem. 1975 Aug;53(8):930-3. doi: 10.1139/o75-129.
The contribution of D-glutamyltransferase (D-GT) (EC 2.3.2.1) to total renal ammonia production was determined by employing DL-methionine-DL-sulfoximine (MSO) as an inhibitor of D-GT. Rat kidney homogenates were assayed for NH3-liberating activity under optimal D-GT or gamma-glutamyltranspeptidase (gamma-GTP) (EC 2.3.2.2) conditions. MSO inhibits only D-GT activity. The contribution of D-GT to total renal ammonia production was then evaluated in the isolated perfused rat kidney employing identical substrate (5 mM L-glutamine) and inhibitor (15 mM MSO) concentrations as employed in the homogenate study. Under these conditions, MSO inhibits 70 percent of the total ammonia production by the normal kidney; in addition, the ratio of ammonia produced per glutamine taken up rose from 1.0 to 1.8. In kidneys from chronically acidotic rats, MSO reduced total ammonia production only 35 percent while the NH3/glutamine ratio rose from 1.0 to 1.8. D-GT appears to be the predominant source of NH3 production in the normal rat kidney; gamma-GTP does not contribute significantly. The rise in the NH3/glutamine ratio after D-GT inhibition is consistent with glutamine utilization via the activated mitochondrial glutaminase (EC 3.5.1.2)-glutamate dehydrogenase (EC 1.4.1.2) pathway.
通过使用DL-蛋氨酸-DL-亚砜亚胺（MSO）作为D-谷氨酰胺转移酶（D-GT，EC 2.3.2.1）的抑制剂，来确定其对肾脏总氨生成的贡献。在最佳D-GT或γ-谷氨酰转肽酶（γ-GTP，EC 2.3.2.2）条件下，对大鼠肾脏匀浆进行氨释放活性测定。MSO仅抑制D-GT活性。然后，在分离灌注的大鼠肾脏中，采用与匀浆研究相同的底物（5 mM L-谷氨酰胺）和抑制剂（15 mM MSO）浓度，评估D-GT对肾脏总氨生成的贡献。在这些条件下，MSO抑制正常肾脏总氨生成的70%；此外，每摄取一分子谷氨酰胺所产生的氨的比例从1.0升至1.8。在慢性酸中毒大鼠的肾脏中，MSO仅使总氨生成减少35%，而氨/谷氨酰胺比例从1.0升至1.8。D-GT似乎是正常大鼠肾脏中氨生成的主要来源；γ-GTP的贡献不显著。D-GT被抑制后氨/谷氨酰胺比例的升高，与通过活化的线粒体谷氨酰胺酶（EC 3.5.1.2）-谷氨酸脱氢酶（EC 1.4.1.2）途径利用谷氨酰胺一致。
