A biosynthesis

O-antigen is added in the periplasm. 0-antigen is not essential for the viability of E. coli, and is in fact missing from E. coli K12, making it avirulent and safe for laboratory use. Details of the synthesis of the O-antigen and core region are outside the scope of this discussion and can be found in a review by Raetz [16]. 

The pathway of lipid A synthesis has been determined mainly in the laboratory of Raetz (Fig. 7) (C.R. Raetz, 2002). The first step in lipid A synthesis is the reversible transfer of the p-hydroxymyristoyl group from ACP to UDP-(V-acetylglucosamine (UDP-GlcNAc) by the UDP-GlcNAc acyltransferase (IpxA). Competition between LpxA and the FabZ dehydratase of fatty acid synthesis helps to determine the rate of lipid A synthesis. The second step in the pathway is the deacetylation of UDP-0-acyl-GlcNAc by the zinc-dependent 

The third step is a second P-hydroxymyristoyl-ACP acyltransferase catalyzed by UDP-P- 

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POTRYKUS I (1997) Transgenic rice Oryza sativa) endosperm expressing daffodil Narcissuspseudonarcissus) phytoene synthase accumulates phytoene, a key intermediate of provitamin A biosynthesis , Plant J, 11, 1071-78. 

ROHDICH, F., WUNGSINTAWEEKUL, J., LUTTGEN, H., FISCHER, M., EISENREICH, W., SCHUHR, C.A., FELLERMEIER, M SCHRAMEK, N., ZENK, M.H., BACHER, A., Biosynthesis of terpenoids 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase from tomato, Proc. Natl. Acad. Sci. USA, 2000, 97, 8251-8256. 

Earlier in this chapter, it was mentioned that many of the nonprotein amino acids are components of nonribosomal peptides. During such a biosynthesis, the peptide is attached to a carrier protein through a thioester bond, until chain termination occurs and the final product is released. The carrier protein is posttranslationally modified by the attachment of a phosphopantetheinyl group from coenzyme A. This step gives rise to the active carrier protein with a phosphopantetheine arm upon which amino acids are added to during NRPS. As an example, loading of isoleucine onto the carrier protein is depicted below (Scheme 5). Further details about nonribosomal peptide syntheses and enzymatic reactions can be found in Chapter 5.19. 

Figure 4 (a) Biosynthesis of the peniciiiin precursor ACV by the three-moduie ACV synthetase, (b) Biosynthesis of enterobactin by the iterative enterobactin synthetase. 

Farber, P., and Geisen, R. (2004). Analysis of differentially-expressed ochratoxin A biosynthesis genes in Penicillium nordicum. Eur. J. Plant Pathol. 110, 661-669. 

FIGURE 22-27 Glutathione metabolism, (a) Biosynthesis of glutathione. (b) Reduced form of glutathione. 

Ochoa, S., Mehler, A. H., Komberg, A., Biosynthesis of Dicarboxylic Acids... 

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