Transaminases whole cells

A new development is the industrial production of L-phenylalanine by converting phenylpyruvic add with pyridoxalphosphate-dependent phenylalanine transaminase (see Figure A8.16). The biotransformation step is complicated by an unfavourable equilibrium and the need for an amino-donor (aspartic add). For a complete conversion of phenylpyruvic add, oxaloacetic add (deamination product of aspartic add) is decarboxylated enzymatically or chemically to pyruvic add. The use of immobilised . coli (covalent attachment and entrapment of whole cells with polyazetidine) is preferred in this process (Figure A8.17). 

The aminotransferase class of enzymes (E.C. 2.6.1.x), also known as transaminases, are ubiquitous, PLP-requiring enzymes that have been used extensively to prepare natural L-amino acids and other chiral compounds.30 123 124 The L-aminotransferases catalyze the general reaction shown in Scheme 19.19 where an amino group from one L-amino acid is transferred to an a-keto acid to produce a new L-amino acid and the respective a-keto acid (see also Chapter 3). Those enzymes most commonly used as industrial biocatalysts have been cloned, overexpressed, and generally used as whole-cell or immobilized preparations. These include branched chain aminotransferase (BCAT) (E.C. 2.6.1.42), aspartate aminotransferase (AAT) (E.C. 2.6.1.1), and tyrosine aminotransferase (TAT) (E.C. 2.6.1.5). 

If the transaminase is used in the form of whole cells instead of purified enzyme, the cost of production of chiral amines decreases, since enzyme purification adds... 

AlkL-membrane protein. The latter contributes to the transport of the ester into the cell through the hydrophobic membrane. The hydroxylation proceeds very efficiently leading to the hydroxylated product 52 as well as the aldehyde product 53 through further oxidation. When integrating a recombinant transaminase into the whole-cell catalyst, conversion of the aldehyde 53 then leads to the formation of the target product 54. As an amine donor, L-alanine was used. It is noteworthy that this process technology has been applied on pilot plant scale by Evonik Industries AG in connection with the production of co-amino-lauric acid for polyamide-12 from palm kernel oil [133]. 

Transaminase-Catalyzed Reactions with Whole Cells... 

Given that transaminases are not able to aminate alcohols, one possibility for the synthesis of chiral amino alcohols is an enzyme cascade reaction carried out with whole cells [36]. Three enz3nnes cascaded in series were expressed in E. colt first the alcohol dehydrogenase oxidized tiie alcohol to the corresponding aldehyde, which is converted into the amine by the transaminase as shown in Scheme 29.15. The recycling of pyruvate and cofactor regeneration were achieved by the alanine dehydrogenase. 

The aforementioned disadvantage of whole-cell biotransformation with mass transfer limitation can be avoided by expression of the transaminase on the surface of the cells [107]. But this effort uncovered several drawbacks, like the need for... 

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