Acetylglucosamine, deacetylation

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... 

Chemically chitosan is obtained from the alkaline deacetylation of chitin from the exoskeleton of crustaceans (eg, crabs, shrimp.), forming a-l,4-linked 2-amino-2-deoxy-a-D-glucose (A-acetylglucosamine Fig. 10.3) [5]. 

Chitin is a long-chain polymer of Ai-acetylglucosamine, a derivative of glucose, and normally found in the shells of crabs, lobsters, shrimps, and insects (Fig. 1.11). Chitosan is the partially deacetylated form of chitin and the degree of deacetylation can vary from 60% to 100% in commercial chitosans (Rinaudo, 2006) (Fig. 1.12). 

Another method of deacetylation (enzymatic bioconversion) makes use of enzyme, chitin deacetylase foimd in several fungi and in some insect species [15-17]. It acts by catalyzing deacetylation of N-acetylglucosamine residues, resulting in conversion of chitin to chitosan. 

Chitin, obtained mainly from the cuticle of the marine crustacean, is presently of considerable interest in industrial and medical fields,i 2 since it is a mucopolysaccharide which resembles cellulose structurally and is present in nature as much as cellulose. Deacetylation of the acetamide group at the 2-position in the acetylglucosamine unit of chitin by alkaline hydrolysis yields chitosan, a cationic polyelectrolyte. Chitosan appears more useful than chitin, having both hydroxyl and amino groups which can be modified easily. Therefore, these chitin and chitosan derivatives are finding a broad range of applications. 

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