Alginic acid, biosynthesis

Formation of L-guluronic acid, a component of the alginic acid-like polysaccharide produced by P. aeruginosa and Azotobacter vinelandii, requires special comment. In this case, a polymer built from /3-(l- 4)-linked D-mannosyluronic acid residues serves as an intermediate in the biosynthesis.204,205 Part of the D-mannosyluronic acid residues in the polymer is subjected to an epimerization at C-5 catalyzed by an exocellular enzyme of the micro-organism,205-207 producing a polysaccharide composed of structural blocks that contain only D-mannosyluronic acid or only l-gulosyluronic acid residues, as well %s some having both. The mechanism of the epimerization remains unclear. 

Other examples of exocellular homopolysaccharides whose biosynthetic process has been investigated include D-mannuronan,204,205 an intermediate in the biosynthesis of bacterial alginic acid (mentioned in Section III,l,c), and bacterial cellulose. 

Aldotriouronic acids, 73 Alginic acid, fractionation, 55 L-guluronic acid in, 88 Alkaloids, biosynthesis of, 269 Allose, 2-amino-2-deoxy-n-, derivatives of, 191... 

The biosynthesis of alginic acid [69, 243, 244] has been investigated in both seaweeds and bacteria. Azotobacter vinelandii produces exopolysaccharide in a high carbon-low nitrogen environment and hexoses, disaccharides and D-mannitol can all provide a carbon source. This bacterium contains enzymes that convert hexose phosphates into GDPMan (reactions A to D and J) which then undergoes oxidation and polymerisation... 

Pindar, D. R, Bucke, C. The biosynthesis of alginic acid by Azotobacter vinelandii. J Biochem 1975,152, 617-622. 

Quillet, M. and de Lestang-Bremond, G. (1985) Sorbitol, a precursor of L-guluronic acid in alginic add biosynthesis. Phytochemistry, 24, 43-45. 

Iota-carrageenans can also strongly bind heavy metal The biosynthesis of a-L-guluronic acid occurs via the cations such as a degradation product of radioactive enzymatic epimerization of (3-D-mannuronic acid (Chapter strontium, and Pb within pH range from 4.0 to 6.0 14), and it is accepted that alginic acids are formed by... 

For example, the biosynthesis of alginate involves GDP-mannuronic acid (GDP-ManA) as NDP-Glx, bactoprenol as the lipid, and a glycosyltransferase that inserts a second mannuronate residue (as Z). 

The cell as a biosynthesis machine can use cheap carbon sources (waste products) as precursor substrates to produce bacterial polymers. However, the in vitro synthesis of biopolymers requires costly purified key enzymes and precursor molecules such as ATP, coal, coal bolsters, and nucleotide sugars or sugar acids to synthesize polymers such as PHA, cellulose, alginate, and PGA. Consequently, these polymers have limited commercial applicability due to their very high production costs. It is estimated the production of PHB by in vitro synthesis would amount to a cost of around US 286,000 per gram of PHB whereas, bacterial production of PHB was estimated to cost about 0.0025 per gram of PHB, and this is still 5-10 times as expensive to produce as the respective petroleum-based polymers. 

Studies with alginate lyases have revealed the presence of 0-acetyl groups in bacterial alginates. The 0-acetyl groups may ensure that some of the D-mannopyranosyluronic acid residues do not epimerize during the biosynthesis of alginates. 

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