Amino Acid Production
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Amino Acid Production HIDEHIKO KUMAGAI
Introduction The water extract of a marine algae “kelp” (Laminaria japonica) has been used in a number of Japanese recipes as a kind of soup to flavor cooking. The tasty (“Umami” in Japanese) factor in the marine algae was identified as monosodium glutamate by Prof. Kikunae Ikeda in 1908. Soon thereafter, Ajinomoto Co. Ltd. started to produce monosodium glutamate by extraction from wheat protein after hydrolysis with hydrochloric acid. In 1956, Kyowa Hakko Kogyo Co. Ltd. succeeded in producing sodium glutamate by using a bacterium (Corynebacter glutamicum). Then, production using microbial methods of various amino acids (including of L-alanine, Laspartic acid, L-arginine, L-citrulline, L-cysteine, L-DOPA [3,4-dihydroxyphenylalanine], Lglutamic acid, L-glutamine, glutathione, L-histidine, D-hydroxyphenylglycine, L-hydroxyproline, L-isoleucine, L-lysine, L-ornithine, Lphenylalanine, D-phenylglycine, L-polylysine, Lproline, L-serine, L-threonine, L-tryptophan, and L-tyrosine) was investigated and successfully manufactured on an industrial scale. Glycine is produced by chemical methods because the molecule has no chiral center, and methionine is also produced by chemical methods in its racemic form because the main use of the amino acid is as feedstuff. D-Methionine is metabolized in animals by the action of D-amino acid oxidase. These amino acids were useful as sources of medicines, food additives, feedstuffs, and starting materials for chemical synthesis. The microbial methods for the production of amino acids are either fermentative or enzymatic. Fermentation methods use cheap carbon and nitrogen sources as the starting materials to produce rather large amounts of amino acids. These starting materials are metabolized by a number of enzymatic reaction steps and the product accumulates in the culture medium during cell growth. Enzymatic methods require substrates that are generally expensive because they usually are produced by chemical synthesis. So this method is suitable for rather expensive, small-scale produc-
tion. Figure 1 shows the difference between fermentative and enzymatic methods. This chapter describes the microbial production of some amino acids including the producing strains, production method, product usage, and industrial production.
L-Alanine The annual world production of L-alanine is about 500 tons. This amino acid is useful as an enteral and parenteral nutrient and as a food additive, which has a sweet taste and bacteriostatic properties. L-Alanine is produced from L-aspartate by a one-step enzymatic method using aspartate βdecarboxylase (Chibata et al., 1986). L-Alanine production by fermentation is difficult because bacteria usually have an alanine racemase to racemize the product. Fermentative production of L-alanine with racemase-deficient strains of Corynebacterium glutamicum, Brevibacterium flavum and Arthrobacter oxydans (Hashimoto and Katsumata, 1999) has been investigated and good yields have been report
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