Amino acid synthetase/glutamate

The enzymes glutamate dehydrogenase, glutamine synthetase, and aminotransferases occupy central positions in amino acid biosynthesis. The combined effect of... 

In earlier studies the in vitro transition metal-catalyzed oxidation of proteins and the interaction of proteins with free radicals have been studied. In 1983, Levine [1] showed that the oxidative inactivation of enzymes and the oxidative modification of proteins resulted in the formation of protein carbonyl derivatives. These derivatives easily react with dinitrophenyl-hydrazine (DNPH) to form protein hydrazones, which were used for the detection of protein carbonyl content. Using this method and spin-trapping with PBN, it has been demonstrated [2,3] that protein oxidation and inactivation of glutamine synthetase (a key enzyme in the regulation of amino acid metabolism and the brain L-glutamate and y-aminobutyric acid levels) were sharply enhanced during ischemia- and reperfusion-induced injury in gerbil brain. 

Figure 9.44 Chromatogram of assay of asparagine synthetase. Peaks 1, o-phthaldialdehyde aspartate 2, glutamate 3, asparagine 4, glutamine. A mixture of 0.025 mAf of each amino acid was made and 20 yu.L injected. (From Unnithan et al., 1984.)...

Glutamine synthetase and glutamic acid decarboxylase catalyze the conversion of glutamic acid to glutamine and y-aminobutyric acid (GABA), respectively. Since both activities are involved in the metabolism of this amino acid, it would be useful to be able to study both simultaneously. And indeed, an HPLC method was developed to measure both activities in crude extracts. 

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