|Maitra, U.; Dekker, E.
|Purification of rat liver gamma-hydroxyglutamate transaminase and its probable identity with glutamate-aspartate transaminase.
|Biochim Biophys Acta
|1. An enzyme which catalyzes the transamination of gamma-hydroxyglutamate has been purified over 300-fold from rat-liver homogenates.
2. The following observations strongly suggest that gamma-hydroxyglutamate transminase is identical with glutamate-aspartate transaminase (-aspartate: 2-oxo-glutarate aminotransferase, EC 18.104.22.168): a, at all stages of purification from either rat-liver or pig-heart extracts, the glutamate to gamma-hydroxyglutamate transminase ratios are not significantly different; b, transaminase activity for both substrates declines at the same rate during controlled heat denaturation of the purified rat-liver enzyme; c, transamination of gamma-hydroxyglutamate is strongly inhibited by either -glutamate or -aspartate; d, glutarate and maleate function as competitive inhibitors for either glutamate or γ-hydroxyglutamate and determined K1 values for a given inhibitor are the same for either amino acid; and e, the purified rat-liver enzyme has the same pH-activity curve for both substrates.
3. The erythro- and threo-isomers of gamma-hydroxy--glutamate serve as substrates for both isozymes of the rat-liver enzyme as well as for the pig-heart enzyme, although the former isomer is a somewhat better substrate. The corresponding -diastereo-isomers are enzymically inactive.
4. With gamma-hydroxyglutamate, only gamma-ketoglutarate and oxaloacetate serve as amino group acceptors; pyruvate, alpha-ketobutyrate, and beta-phenylpyruvate are inactive.
5. Other gamma-substituted forms of glutamic acid, including gamma-methyleneglutamic acid and gamma-hydroxy-gamma-methylglutamic acid, are also active with the purified enzymes.