Purification and characterization of glutamic acid dehydrogenase and α-ketoglutaric acid reductase from Peptococcus aerogenes

1972 ◽  
Vol 18 (6) ◽  
pp. 881-892 ◽  
Author(s):  
W. M. Johnson ◽  
D. W. S. Westlake
Keyword(s):  
Glutamic Acid ◽  
Kinetic Data ◽  
Acid Metabolism ◽  
The Other ◽  
Keto Acid ◽  
Glutamate Metabolism ◽  
Purification And Characterization ◽  
Acid Dehydrogenase ◽  
Acid Reduction

Two NAD-dependent enzymes involved in glutamic acid metabolism have been isolated from cell-free extracts of P. aerogenes. One enzyme, glutamic acid dehydrogenase, was shown to oxidatively deaminate glutamic acid yielding α-ketoglutaric acid in the presence of NAD but not NADP. The other enzyme, an NADH-requiring α-ketoglutarate reductase, reduced the α-keto acid to α-hydroxy-glutarate. The two NAD-dependent enzymes were separated, purified, and characterized. The results indicate that glutamic acid dehydrogenase, an enzyme not frequently implicated in anaerobic glutamate metabolism, is a predominating protein in extracts of P. aerogenes grown in the presence of glutamate. Kinetic data showed that the equilibrium of the latter reaction favored the direction of keto acid reduction.

Alpha-ketoglutarate as an intermediate in glutamate metabolism by Peptococcus aerogenes

1972 ◽  
Vol 18 (6) ◽  
pp. 875-880 ◽  
Author(s):  
W. M. Johnson ◽  
D. W. S. Westlake
Keyword(s):  
Potential Energy ◽  
Glutamic Acid ◽  
Tca Cycle ◽  
The Other ◽  
Glutamate Metabolism ◽  
Fermentation Products ◽  
Acid Dehydrogenase ◽  
Specific Distribution ◽  
The Tca Cycle ◽  
Hydroxyglutaric Acid

The pathway from glutamic acid to α-hydroxyglutaric acid in Peptococcus aerogenes proceeds via α-ketoglutaric acid and is mediated by two NAD-dependent enzymes. One enzyme, an NAD-dependent glutamic acid dehydrogenase, oxidatively deaminates glutamic acid to α-ketoglutaric acid. The other enzyme, α-ketoglutaric acid reductase, reduces α-ketoglutaric acid to α-hydroxyglutaric acid in the presence of NADH. The demonstration of a very low level of α-ketoglutaric acid dehydrogenase activity in crude cell-free extracts indicates that the primary metabolic pathway for glutamic acid carbons proceeds via α-hydroxyglutaric acid and not via the TCA cycle. Potential energy-yielding mechanisms are discussed relative to the known specific distribution of glutamic acid carbon atoms in fermentation products.

scholarly journals Alteration in gene expression of branched-chain keto acid dehydrogenase kinase but not in gene expression of its substrate in the liver of clofibrate-treated rats

1996 ◽  
Vol 317 (2) ◽  
pp. 411-417 ◽  
Author(s):  
Harbhajan S. PAUL ◽  
Wei-Qun LIU ◽  
Siamak A. ADIBI
Keyword(s):  
Gene Expression ◽  
Rat Liver ◽  
Fold Increase ◽  
Branched Chain Amino Acids ◽  
The Other ◽  
Mrna Levels ◽  
Keto Acid ◽  
Protein Mass ◽  
Acid Dehydrogenase ◽  
Branched Chain

We previously showed that the oxidation of branched-chain amino acids is increased in rats treated with clofibrate [Paul and Adibi (1980) J. Clin. Invest. 65, 1285–1293]. Two subsequent studies have reported contradictory results regarding the effect of clofibrate treatment on gene expression of branched-chain keto acid dehydrogenase (BCKDH) in rat liver. Furthermore, there has been no previous study of the effect of clofibrate treatment on gene expression of BCKDH kinase, which regulates the activity of BCKDH by phosphorylation. The purpose of the present study was to investigate the above issues. Clofibrate treatment for 2 weeks resulted in (a) a 3-fold increase in the flux through BCKDH in mitochondria isolated from rat liver, and (b) a modest but significant increase in the activity of BCKDH. However, clofibrate treatment had no significant effect on the mass of E1α, E1β, and E2 subunits of BCKDH or the abundance of mRNAs encoding these subunits. On the other hand, clofibrate treatment significantly reduced the activity, the protein mass and the mRNA levels of BCKDH kinase in the liver. In contrast to the results obtained in liver, clofibrate treatment had no significant effect on any of these parameters of BCKDH kinase in the skeletal muscle. In conclusion, our results show that clofibrate treatment increases the activity of BCKDH in the liver and the mechanism of this effect is the inhibition of gene expression of the BCKDH kinase.

scholarly journals The case for regulating indispensable amino acid metabolism: the branched-chain α-keto acid dehydrogenase kinase-knockout mouse

2006 ◽  
Vol 400 (1) ◽  
Author(s):  
Susan M. Hutson
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Essential Amino Acids ◽  
The Body ◽  
Keto Acid ◽  
Acid Dehydrogenase ◽  
Indispensable Amino Acid ◽  
Branched Chain

BCAAs (branched-chain amino acids) are indispensable (essential) amino acids that are required for body protein synthesis. Indispensable amino acids cannot be synthesized by the body and must be acquired from the diet. The BCAA leucine provides hormone-like signals to tissues such as skeletal muscle, indicating overall nutrient sufficiency. BCAA metabolism provides an important transport system to move nitrogen throughout the body for the synthesis of dispensable (non-essential) amino acids, including the neurotransmitter glutamate in the central nervous system. BCAA metabolism is tightly regulated to maintain levels high enough to support these important functions, but at the same time excesses are prevented via stimulation of irreversible disposal pathways. It is well known from inborn errors of BCAA metabolism that dysregulation of the BCAA catabolic pathways that leads to excess BCAAs and their α-keto acid metabolites results in neural dysfunction. In this issue of Biochemical Journal, Joshi and colleagues have disrupted the murine BDK (branched-chain α-keto acid dehydrogenase kinase) gene. This enzyme serves as the brake on BCAA catabolism. The impaired growth and neurological abnormalities observed in this animal show conclusively the importance of tight regulation of indispensable amino acid metabolism.

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