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Differences in 2-oxoglutarate dehydrogenase regulation in liver and kidney.

ABSTRACT: In response to acidosis, renal ammoniagenesis is stimulated, enhancing urinary buffering power, while hepatic ammoniagenesis and ureagenesis decrease, so as to spare bicarbonate consumed in the urea cycle. 2-Oxoglutarate (2-OG) levels can regulate ammoniagenesis in kidney and gluconeogenesis in liver and kidney. Since the activity of 2-oxoglutarate dehydrogenase (2-OGDH) has an important influence on cellular levels of 2-OG, this study evaluated the effects of pH on 2-OGDH in liver and kidney and found that: (1) the isolated enzyme from both organs has the same pH-sensitivity; (2) 2-OGDH flux measured in intact mitochondria was inhibited by increasing H+ in liver, but stimulated in kidney; (3) transport of 2-OG into the mitochondria was not rate-limiting; (4) liver mitochondrial 2-OGDH exhibited a strong preference for 2-OG generated within the mitochondria from glutamate-oxaloacetate transaminase (GOT), suggesting that channelling between GOT and 2-OGDH occurs. Since complexation between 2-OGDH and GOT occurs in vitro, we propose that the degree of complexation is higher in liver than in kidney, such that most of the 2-OGDH may be complexed to GOT in liver. In the liver the inherent H(+)-sensitivity of 2-OGDH is masked by the pH-sensitivity of GOT and the glutamate-aspartate carrier.

SUBMITTER: Smith BC

PROVIDER: S-EPMC1132613 | biostudies-other | 1992 Jun

REPOSITORIES: biostudies-other

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Project description:Inhibition of lysyl hydroxylase and prolyl 3-hydroxylase was studied with 23 selected aromatic and aliphatic structural analogues of 2-oxoglutarate and the results were compared with those previously reported for prolyl 4-hydroxylase. All the compounds inhibited the hydroxylases competitively with respect to 2-oxoglutarate and noncompetitively with respect to Fe2+ and the peptide substrate. The inhibition patterns for the three collagen hydroxylases were basically similar, but certain differences in detail emerged. One systematic difference was that lysyl hydroxylase had a higher Ki for almost all the compounds than had the two prolyl hydroxylases. Another interesting difference was that pyridine-2,4-dicarboxylate was the most potent inhibitor of lysyl hydroxylase and prolyl 3-hydroxylase, with Ki values of 50 microM and 3 microM respectively, whereas pyridine-2,5-dicarboxylate was the most potent inhibitor of prolyl 4-hydroxylase. These and other data suggest that the three collagen hydroxylases have similar but not identical 2-oxoglutarate-binding sites. Pyridine-2,4-dicarboxylate and pyridine-2,5-dicarboxylate and their corresponding benzene derivatives were also found to inhibit 2-oxoglutarate dehydrogenase, but with this enzyme, unlike the collagen hydroxylases, no distinct difference in the Ki values was found between the corresponding pyridine and benzene derivatives. This demonstrates the importance of the metal ion for the binding of various compounds at the 2-oxoglutarate-binding site of the collagen hydroxylases. 2-Oxoadipate was shown to replace 2-oxoglutarate in the lysyl hydroxylase and 2-oxoglutarate dehydrogenase reactions, as has previously been reported for prolyl 4-hydroxylase, whereas no other 2-oxo acid tested had any co-substrate activity. The 2-oxoglutarate-binding site of these enzymes is thus flexible to a certain degree, as it can accommodate molecules of different shapes and volumes. On the basis of the present data pyridine-2,5-dicarboxylate seems to be a quite specific inhibitor of prolyl 4-hydroxylase, the Ki for 2-oxoglutarate dehydrogenase being about 4000-fold higher.

Project description:Both hypoxia and inhibition of 2-oxoglutarate dehydrogenase complex (OGDHC) are known to change cellular amino acid pools, but the quantitative comparison of the metabolic and physiological outcomes has not been done. We hypothesize that OGDHC inhibition models metabolic changes caused by hypoxia, as both perturb the respiratory chain function, limiting either the NADH (OGDHC inhibition) or oxygen (hypoxia) supply. In the current study, we quantify the changes in the amino acid metabolism after OGDHC inhibition in the highly sensitive to hypoxia cerebellum and compare them to the earlier characterized changes after acute hypobaric hypoxia. In addition, the associated physiological effects are characterized and compared. A specific OGDHC inhibitor succinyl phosphonate (SP) is shown to act similar to hypoxia, increasing levels of many amino acids in the cerebellum of non-pregnant rats, without affecting those in the pregnant rats. Compared with hypoxia, stronger effects of SP in non-pregnant rats are observed on the levels of cerebellar amino acids, electrocardiography (ECG), and freezing time. In pregnant rats, hypoxia affects ECG and behavior more than SP, although none of the stressors significantly change the levels of cerebellar amino acids. The biochemical differences underlying the different physiological actions of SP and hypoxia are revealed by correlation analysis of the studied parameters. The negative correlations of cerebellar amino acids with OGDHC and/or tryptophan, shown to arise after the action of SP and hypoxia, discriminate the overall metabolic action of the stressors. More negative correlations are induced in the non-pregnant rats by hypoxia, and in the pregnant rats by SP. Thus, our findings indicate that the OGDHC inhibition mimics the action of acute hypobaric hypoxia on the cerebellar amino acid levels, but a better prediction of the physiological outcomes requires assessment of integral network changes, such as increases in the negative correlations among the amino acids, OGDHC, and/or tryptophan.

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Differences in 2-oxoglutarate dehydrogenase regulation in liver and kidney.

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