Biochemical characterization of partially purified gaba : pyruvate transaminase from Nicotiana tabacum

Pyruvate-dependent 4-aminobutyrate transaminase (EC 2.6.1.19) activity in c rude extracts or lysed mitochondrial preparations from tobacco (Nicotiana t abacum L. cv Samsun N.N.) leaf was separated from 2-oxoglutarate-dependent GABA-T activity by FPLC anion exchange chromatography. Pyruvate-dependent G ABA-T was partially purified 1530-fold by a combination of mitochondrial is olation and FPLC anion-exchange chromatography. This enzyme preparation had an apparent K-m of 1.2 +/- 0.2 mM for GABA and 0.24 +/- 0.05 mM for pyruva te. Two-oxoglutarate-dependent GABA-T activity was not detected in the part ially purified preparation. Our data indicate the existence of a pyruvate-s pecific mitochondrial GABA-T. (C) 1999 Elsevier Science Ltd. All rights res erved.