Aminotransferases Bacteria

Racemization. A proton can be added back to the original alpha position but without stereospecificity. A racemase which does this is important to bacteria. They must synthesize D-alanine and D-glu-tamic acid from the corresponding L-isomers for use in formation of their peptidoglycan envelopes.153-1543 The combined actions of alanine racemase plus D-alanine aminotransferase, which produces D-glutamate as a product, provide bacteria with both d amino acids. 

Bacteria, gut micToflora, 142, 143, 147-150 Bactemdes, 14 , 149 Banana, starch content, 139 BarorEceptor , 712 Basal level of transcription, 5 5 Basal metabolic rate (BMR), 302, 735-736 BCAA aminotransferase, 209, 430,433,434, 343... 

Lysine is formed in bacteria by decarboxylation of meso-diamino-pimelic acid (Fig. 24-14). Glycine is decarboxylated oxidatively in mitochondria in a sequence requiring lipoic acid and tetrahydrofolate as well as PLP (Fig. 15-20). A methionine decarboxylase has been isolated in pure form from a fem. ° The bacterial dialkylglycine decarboxylase is both a decarboxylase and an aminotransferase which uses pyruvate as its second substrate forming a ketone and L-alanine as products (See Eq. 

The reductant can be NADH, NADPH (in yeast and bacteria), or reduced ferredoxin (in plants). The enzyme that catalyzes this reaction is glutamate synthase it is also known as glutamate oxoglutarate aminotransferase (GOGAT). A GS/GOGAT complex exists in plants and allows them to cope with conditions of limited nitrogen availability. Enzymes that catalyze transamination reactions require pyridoxal phosphate as a coenzyme (Figure 23.8). We discussed this compound in Section 7.8 as a typical example of a coenzyme, and here we can see its mode of action in context. 

Fig. 5. Pretyrosine pathway. An alternate route for synthesis of phenylalanine and tyrosine described in bacteria and fungi. Enzymes labeled (a), (b), and (c) denote prephenate aminotransferase, pretyrosine dehydratase, and pretyrosine dehydrogenase, respectively.

The potential of biotransformations with genetically modified microorganisms can be illustrated by the following example, where the chain of added-value to amino acid products is also recognisable The Mercian Company (Japan) uses a recombinant E. coli strain to prepare (S)-piperidine-2-car-boxylic acid from (L)-lysine. In this strain, the (L)-lysine-permease transport system is overexpressed, so that in this pathway lysine is produced efficiently in the cells. The bacteria possess additionally a (L)-lysine-aminotransferase from Flavobacterium lutescens, which brings about the deamination of lysine. The thus generated aldehyde is in equilibrium with its intramolecular imine, which, in presence of the E. co/i-specific pyrroline-5-carboxylate reductase, is reduced with NADPH to (S)-piperidine-2-carboxylic acid. The turnover... 

Although it is widely held that glutamate semialdehyde is the substrate of the final step (with di-aminovalerate as a possible enzyme-bound intermediate), some authorities claim that 4,5-dioxo-valerate is an intermediate, and that this is converted into 5-aminolevulinate by 4,5-dioxovale-rate aminotransferase. The latter enzyme is present in plants and bacteria, but does not always display high activity. 

Figure 2 Lysine metabolism and its relationship to a aminoadipic acid production in bacteria atnl fungi. Abbreviation LAT, lysine e aminotransferase.

L-Phenylalanine aminotransferases (classified as tyrosine aminotransferase, E.C. 2.6.1.5 which also acts on phenylalanine) are enzymes useful in L-phenylalanine synthesis, as mentioned above, and have been studied in various thermophilic bacteria by Schutten et al. [185]. These workers looked at several Bacillus isolates... 

Pedraza RO, Ramirez-Mata A, Xiqui ML, Baca BE (2004) Aromatic amino acid aminotransferase activity and indole-3-acetic acid production by associative nitrogen-fixing bacteria. FEMS Microbiol Lett 233 15-21... 

Figure 1.3. Diagram of the proteolytic systems of lactic acid bacteria, (a) Extracellular components PrtP, cell-envelope proteinase PrtM, proteinase maduration protein Opp, oligopetide permease DtpT, the ion linked trasnsporter for di-and tripeptides and Opt, the ABC transporter for peptides, (b) Intracelullar components pool of about 20-25 peptidases, including general (PepN, PepC) and specific (PepX, PepQ) peptidases, and amino acid catabolic enzymes (carboxylases, aminotransferases, etc.).

Matsuhashi, S., and D. N. Dietzler Thymidine diphosphate 4-keto-6-deoxy-D-glucose-L-glutamate-aminotransferase in bacteria. Federation Proc. 23, 170 (1964). 

---