The γ-aminobutyric acid shunt in germinating Sinapis alba seeds

Abstract

The metabolism of glutamic acid via the γ-aminobutyric acid (GABA) shunt was investigated during the germination of Sinapis alba by comparing the 14CO 2 evolved from germinating seeds after feeding samples with either L-[U- 14C] glutamate, [U- 14C]GABA or L-[1- 14C]glutamate. Glutamate appeared to be metabolised mainly via GABA during imbibition but was metabolised via 2-oxoglutarate during later stages of germination. Glutamate decarboxylase may be more active than other enzymes at low levels of hydration so that initially glutamate was converted to γ-aminobutyrate and was then oxidised in the Krebs tricarboxylic acid cycle via succinate. Later, at higher levels of hydration glutamate was metabolised to 2-oxoglutarate which was then oxidised, again via the Krebs tricarboxylic acid cycle.