Studies in Amino Acid Biogenesis: the Synthesis of Alanine from Pyruvate and Ammonia

Abstract

SUMMARY:Washed suspensions of certain bacteria can synthesize alanine from pyruvate and ammonia. This has been studied in detail in Bacillus subtilis. Several other amino acids can be formed from the corresponding keto-acids, but synthesis was most rapid in the case of alanine. Notably, glutamic acid is formed from ketoglutarate relatively slowly, whilst oxalacetate fails to give aspartate. Pyruvate can accept an amino group from a number of amino acids by transamination (but aspartic and glutamic acids are less effective than ammonia itself). It is possible that the reductive amination of pyruvate may proceed directly rather than through transamination from some other primary amino-acceptor.The last step in the synthesis of an amino acid is often the exchange of the carbonyl group of the appropriate keto acid for an amino group. When the ultimate source of the latter is ammonia we can refer to the reaction as

Amino Acid Requirements for Formation of the Reductive Amination System in Bacillus subtilis

“…BacilZus subtilis 4 (Fairhurst et al 1956), maintained on nutrient agar slopes, was used throughout.…”

“…1~ total phosphate. Choice of incubation time was important since Fairhurst et al (1956) found that reductive amination activity decreased very sharply towards the end of the logarithmic phase of growth. The use of a constant incubation-time with different media giving rise to different rates of growth might therefore produce changes in enzyme activity arising solely from differences in the ' physiological age' of the cultures when harvested.…”

“…Measurement of enzyme activity (Fairhurst et al 1956) : buffered bacterial suspension (2 ml. ), 0-5 M-sodium pyruvate (1 ml.)…”

“…The development of the reductive amination system may depend critically on a number of factors, some of which are not known (cf. Fairhurst et al 1956), and the interpretation of the effects of various additions to the medium requires great caution.…”

Optical Activity of Amino Acids Formed by Reductive Amination in Bacillus subtilis

“…When leucine and valine are formed from the analogous keto acids, only the L-isomer is found. Since B. subtilis has a racemase active for alanine but not for valine or leucine, it is possible that the L-alanine may be the primary product and which is then racemized.Suspensions of Bacillus subtilis and of some other organisms can synthesize certain amino acids from ammonia and the corresponding keto-acids (Fairhurst, King & Sewell, 1956). When alanine is formed from pyruvate by B. subtilis, the racemic DL-mixture is produced.…”