Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.4.1.2 (glutamate dehydrogenase)
 4,380 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hyperthermophilic archaeon (formerly archaebacterium) Thermococcus litoralis grows at temperatures up to 98 degrees C using peptides and proteins as the sole sources of carbon and nitrogen. Cell-free extracts of the organism contained two distinct types of aromatic aminotransferases (EC 2.6.1.57) which were separated and purified to electrophoretic homogeneity. Both enzymes are homodimers with subunit masses of approximately 47 kDa and 45 kDa. Using 2-oxoglutarate as the amino acceptor, each catalyzed the pyridoxal-5'-phosphate-dependent transamination of the three aromatic amino acids but showed virtually no activity towards aspartic acid, alanine, valine or isoleucine. From the determination of Km and kcat values using 2-oxoglutarate, phenylalanine, tyrosine and tryptophan as substrates, both enzymes were shown to be highly efficient at transaminating phenylalanine (kcat/Km approximately 400 s-1 mM-1); the 47-kDa enzyme showed more activity towards tyrosine and tryptophan compared to the 45-kDa one. Kinetic analyses indicated a two-step mechanism with a pyridoxamine intermediate. Both enzymes were virtually inactive at 30 degrees C and exhibited maximal activity between 95-100 degrees C. They showed no N-terminal sequence similarity with each other (approximately 30 residues), nor with the complete amino acid sequences of aromatic aminotransferases from Escherichia coli and rat liver. The catalytic properties of the two enzymes are distinct from bacterial aminotransferases, which have broad substrate specificities, but are analogous to two aromatic aminotransferases which play a biosynthetic role in a methanogenic archaeon. In contrast, it is proposed that one or both play a catabolic role in proteolytic T. litoralis in which they generate glutamate and an arylpyruvate. These serve as substrates for glutamate dehydrogenase and indolepyruvate ferredoxin oxidoreductase in a novel pathway for the utilization of aromatic amino acids.
 ...
PMID:Characterization of aromatic aminotransferases from the hyperthermophilic archaeon Thermococcus litoralis. 812 13

Pyrococcus furiosus is a strictly anaerobic archaeon that grows optimally at 100 degrees C by a fermentative-type metabolism in which complex peptide mixtures such as yeast extract and Tryptone, and also certain sugars, are oxidized to organic acids, H2 and CO2. Enzymes involved in the utilization of peptides such as proteases, aromatic amino transferases, and glutamate dehydrogenase have been previously purified from this organism. It is shown here that P. furiosus also contains significant cytoplasmic concentrations of a new enzyme termed indolepyruvate ferredoxin oxidoreductase (IOR). This catalyzes the oxidative decarboxylation of aryl pyruvates, which are generated by the transamination of aromatic amino acids, to the corresponding aryl acetyl-CoA. IOR is a tetramer (alpha 2 beta 2) of two identical subunits (66,000 and 23,000 Da) with a molecular weight of 180,000. The enzyme contains one molecule of thiamine pyrophosphate and four [4Fe-4S]2+,1+ and one [3Fe-4S]0,1+ cluster, as determined by iron analyses and EPR spectroscopy. Significant amounts of other metals such as copper and zinc were not detected. IOR was virtually inactive at 25 degrees C and exhibited optimal activity above 90 degrees C (at pH 8.0) and at pH 8.5-10.5 (at 80 degrees C). The enzyme was sensitive to inactivation by O2, losing 50% of its activity after exposure to air for 20 min at 23 degrees C, and was quite thermostable, with a half-life of activity at 80 degrees C (under anaerobic conditions) of about 80 min. The Km values (in microM) for indolepyruvate, p-hydroxyphenylpyruvate, phenylpyruvate, CoASH, and P. furiosus ferredoxin, the physiological electron carrier, were 250, 110, 90, 17, and 48, respectively. IOR was inhibited by KCN (apparent Ki = 7.5 mM), but not by CO (1 atm). An enzyme analogous to IOR has not been reported previously. Curiously, it has few properties in common with the pyruvate ferredoxin oxidoreductase of P. furiosus, even though the two enzymes catalyze virtually identical reactions. In fact, of known ketoacid oxidoreductases, the catalytic mechanism of IOR appears to be most similar to that of the pyruvate ferredoxin oxidoreductase from the hyperthermophilic bacterium Thermotoga maritima.
 ...
PMID:Indolepyruvate ferredoxin oxidoreductase from the hyperthermophilic archaeon Pyrococcus furiosus. A new enzyme involved in peptide fermentation. 820 94