Amino epimerase

Conversion to penicillin N is achieved by an epimerase that converts the L configuration amino group into the D configuration. 

Figure 11.5 Amino acid building blocks are incorporated into daptomycin backbone successively by NRPS subunits DptA, DptBC and DptD (a). Structural diversity of daptomycin peptide core can be obtained by genetic modifications of dpt gene cluster (b). C, condensation domain A, adenylation domain PCP, peptidyl carrier protein E, epimerase TE, thioesterase domain... 

Many DOHs, such as L-mycarose, L-epivancosamine, L-noviose or L-dauno-samine, show an L configuration. Formation of L-DOH requires the action of a 5- or 3,5-epimerase. The epimerase EvaD from the biosynthesis pathway of L-epivancosamine was shown to act as a 5-epimerase on the intermediate thymidine-5 -diphospho-3-amino-2,3,6-trideoxy-D-tIireo-hexopyranos-4-ulose [10]. On the... 

A number of other racemases and epimerases may function by similar mechanisms. While some amino acid racemases depend upon pyridoxal phosphate (Chapter 14), several others function without this coenzyme. These include racemases for aspartate,113 glutamate,114-1153 proline, phenylalanine,116 and diamino-pimelate epimerase.117 Some spiders are able to interconvert d and l forms of amino acid residues in intact polypeptide chains.118119... 

The amino acid sequence deduced from ORF 23 (mnaA) shared homology with bacterial A-acetylglucosamine 2-epimerases that convert A-acetyl-glucosamine into A-acetylmannosamine, a precursor of sialic acids. ORF 9 and ORF 24 (neuB) both produce polypeptides that exhibited 25 and 31%... 

The biosynthesis of CPC is well known. The first step of CPC synthesis is the formation of the tripeptide S-(L-a-aminoadipyl)-L-cysteinlyl-D-valine (LLD-ACV) from L-a-aminoadipinic acid (AAA), L-cystein (CYS ) and D-valine (VAL) by the LLD-ACV synthetase (ACVS). LLD-ACV is converted with the enzyme isopenicillin AT-synthetase (cyclase) to isopenicillin N (IPN) and then with isopenicillin N-epimerase to penicillin N (PEN). The 6-ring is formed by deacetoxycephalosporin C-synthase (expandase). Deacetoxycephalosporin C (DAOC) is converted with deacetoxycephalosporin C-hydroxylase to decacetylcephalosporin C (DAC) and the latter with deacetylcephalosporin C-acyltransferase to CPC (Fig. 1). Except the amino acid and ACV, all others were monitored by on-line HPLC. 

If we consider the requirements for the coupling of the lipid and 13 amino acids, followed by ring closure, the multi-subunit NRPS contains 45 enzymatic functions (13 condensation (C) domains, 13 adenylation (A) domains, 13 thiolation (T) domains, three epimerase (E) domains, one thioesterase (Te) domain, one acyl-CoA ligase and one ACP Figure 14.2). 

Epimerization at C-2 of a sugar nucleotide has been described. An enzyme from Escherichia coli catalyzes the epimerization of UDP-2-acetamido-2-deoxy-D-glucose to UDP-2-acetamido-2-deoxy-D-mannose.59 Such an epimerization, together with the 3,5-epimerase reaction of a 4-ketose and stereospecific reduction at C-4, could lead to inversion at all of the chiral centers of, for instance, 2-amino-2-deoxy-D-glucose. 

The amino acid sequences of known hydantoin racemases present two highly conserved cysteines around positions 75 and 180 (see the asterisks in Figure 12.4). The enzymes involved in the racemization/epimerization of different substrates such as glutamate racemase and diaminopimelate epimerase present two cyste-... 

Amino Acid Racemases and Epimerases Elijah Adams... 

The isomerase class of biocatalysts represents a small number of enzymes that are mainly composed of the racemases, epimerases, and mutases. In the case of racemases and epimerases, the stereochemistry of at least one carbon center is changed, while mutases catalyze the transfer of a functional group, such as an amino function, to an adjacent carbon, forming a new stereocenter. One of the... 

Amino acid racemases and epimerases catalyzing racemization and epimerization at the chiral center containing an NH2 or NH group (E. C. class 5.1.1) ... 

Cofactor-independent Racemases and Epimerases Acting on Amino Acids... 

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