At present, microbial fermentation is the mainstream method for the production of L-Arg. Mutation breeding is a traditional method to obtain industrial fermentation strains, but this method is blind and random, time-consuming and laborious, and it is often difficult to obtain stable high-yielding strains. In order to overcome the shortcomings of mutation breeding, researchers have proposed a variety of molecular breeding methods with the help of gene cloning and expression technology, including increasing the expression of genes related to the L-Arg biosynthesis pathway, reducing or removing the feedback of the final product to key enzymes Inhibit and release the feedback repression of the repressor protein to its biosynthetic genes and replace the expression regulatory elements, etc., in order to achieve the purpose of increasing the production of L-Arg. probioticseverything.com
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L-Arg biosynthesis pathway
In order to improve the production of arginine by molecular breeding, the biosynthetic pathway of arginine should be identified first. There are three main ways for microorganisms to metabolize and synthesize L-Arg, all of which use L-glutamate as a substrate, but through different enzymatic reactions, L-Arg is finally generated. According to the different ways of participating in the acetyl group, the biosynthetic pathways of L-Arg are divided into: probioticseverything.com
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probiotics empty stomach
1.Linear approach
(Pathway I): In microorganisms such as Escherichiacoli, L-glutamic acid is sequentially catalyzed by the corresponding enzymes encoded by argA, argB, argC, etc. to generate L-ornithine, L-citrulline and other metabolites, and finally L-glutamic acid is produced. -Arg. Among them, the acetylglutamate synthase (NAGS) encoded by argA is the key rate-limiting enzyme of this pathway, which is feedback-inhibited by L-Arg. probioticseverything.com
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probiotics empty stomach
2. The economic cycle pathway (pathway II): This pathway mainly exists in microorganisms such as corynebacterium, yeast, etc., such as Corynebacterium glutamicum, Corynebacterium crenatum, Bacillusthermophilus, Saccharom. Compared with pathway I, this pathway introduces ornithine acetyltransferase (OAT), which can not only catalyze the production of N-acetylornithine.
The deacetylation reaction generates ornithine, and its acetyl group can also be transferred to L-glutamic acid to form N-acetylglutamic acid, thereby replacing the acetyl-ornithine enzyme encoded by argA and argE in pathway I In this pathway, N-acetylglutamate kinase (N-acetylglutamate kinase, NAGK) encoded by argB is the key rate-limiting enzyme, which is feedback-inhibited by L-Arg. probioticseverything.com
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3. Special Pathway (Pathway III): In Xanthomonas.
A special arginine synthesis pathway was found in sp. Among them, N-acetylornithine does not generate L-ornithine through deacetylation, but acetylornithine carbamoyltransferase (acetylornithine) encoded by argF. Carbamyltransferase, AOCT) catalyzes the production of N-acetylcitrulline, which is catalyzed by argE-encoded acetylornithase to catalyze the deacetylation of the deacetylated group to L-citrulline, and then to L-arginine succinate to finally synthesize L-Arg. probioticseverything.com
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probiotics empty stomach
