Biochemistry of Amino Acids - A. Majster 1961

General Biochemistry and Physiology of Amino Acid Metabolism
Transamination
Transamination reactions between monocarboxylic amino and keto acids

Until recently, it was widely accepted that glutamic acid or a-ketoglutaric acid was an obligatory participant in all Transamination reactions. Evidence contradicting this view first emerged with the discovery of transamination between glutamine and a-keto acids. The notion that glutamic acid must be involved in every transamination reaction lacks theoretical foundation. However, because transamination reactions involving glutamic acid are so widespread in nature, proving the existence of transamination between monocarboxylic Amino Acids and monocarboxylic keto acids is no easy task. For instance, The transfer of the NH₂ group from valine to Pyruvate can occur either directly or through the coupling of reactions between valine and ketoglutarate and between glutamic acid and pyruvate.

While studying the transaminases of Escherichia coli, an enzyme catalyzing the reversible transamination reaction between Alanine and a-ketoisovaleric acid was discovered and isolated in purified form [272]. This transaminase, which catalyzes the valine ⇄ alanine and valine ⇄ a-aminobutyric acid transamination reactions, was successfully separated from E. coli glutamate transaminases. The detection of this reaction in an E. coli mutant lacking glutamate-valine transaminase, combined with observations showing that the enzyme preparation from E. coli does not catalyze transamination between glutamic acid and alanine, confirms the existence of direct amino group transfer between monocarboxylic amino and a-keto acids. Furthermore, other transaminases mediating reactions between various monocarboxylic amino and a-keto acids have been identified in E. coli (p. 231). Cell extracts of Brucella abortus catalyze several transamination reactions between pyruvate and amino acids, with evidence reported for the partial resolution of leucine-glutamate and leucine-alanine transaminases [295].

Transamination reactions between pyruvate and Amino acids have also been detected in the Liver, although the relative rates of transamination involving glutamic acid versus Other Amino Acids have not been determined [296]. An enzyme catalyzing transamination between Serine and pyruvate has been found in The Liver and Kidneys of certain animals [297]; the reverse reaction between alanine and ß-hydroxypyruvate has also been observed. When alanine is replaced by glutamic acid, aspartic acid, or other amino acids, this enzyme is inactive.

Several other transamination reactions involving monocarboxylic amino and a-keto acids are listed below (see p. 228). Recent data suggest that A wide variety of such reactions exist. Earlier studies likely failed to detect these reactions, partly due to a lack of suitable Methods for assaying the corresponding amino and keto acids, and perhaps also because the a-keto acid analogs of many amino acids were unavailable.