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. 1972 Apr;49(4):579–584. doi: 10.1104/pp.49.4.579

In Vivo and In Vitro Studies on γ-Aminobutyric Acid Metabolism with the Radish Plant (Raphanus sativus, L.)

John G Streeter a,1, John F Thompson a
PMCID: PMC366009  PMID: 16658005

Abstract

Labeled glutamate was rapidly converted to γ-aminobutyrate in intact, excised radish (Raphanus sativus L., var. Champion) leaves. Labeled γ-aminobutyrate was metabolized via succinate and the Krebs cycle and was not carboxylated to form glutamate. Administration of carbon-14 and tritium-labeled succinate indicated that less than 10% of the γ-aminobutyrate formation occurs by amination of succinic semialdehyde. Therefore, most γ-aminobutyrate formation must be via glutamate decarboxylation.

Radish leaf extracts were more active in catalyzing transamination between γ-aminobutyrate and pyruvate than that between γ-aminobutyrate and α-ketoglutarate. Glutamate decarboxylase was approximately 20 times more active than γ-aminobutyrate: pyruvate transaminase. Succinic semialdehyde dehydrogenase was found in the extracts, and NAD was much more active as a hydrogen acceptor than NADP. No reduction of succinate to succinic semialdehyde by the NAD-linked dehydrogenase could be demonstrated. The following pH optima were determined: glutamate decarboxylase, 5.9; γ-aminobutyrate: pyruvate transaminase, 8.9; succinic semialdehyde: NAD dehydrogenase, about 9.0.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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