Action of Azotobacter vinelandii poly-β-d-mannuronic acid C-5-epimerase on synthetic d-glucuronans

Eleven different glucans (wheat starch, potato amylopectin, potato amylose, pullulan, alternan, regular comb dextran, α-cellulose, microcrystalline cellulose, CM-cellulose, chitin, and chitosan) that had their C-6 primary alcohol groups oxidized to carboxyl groups by reaction with 2,2,6,6-tetramethyl-1-piperidine oxoammonium ion (TEMPO), were reacted with Azotobacter vinelandii poly-β-(1→4)-d-mannuronic acid C-5-epimerase. All of the oxidized polysaccharides reacted with the C-5-epimerase, as evidenced by comparing: (1) differences in the relative viscosities; (2) differences in the carbazole reaction; (3) differences in their susceptibility to acid hydrolysis, and (4) differences in their ability to form calcium gels, before and after reaction. We further show the formation of l-iduronic acid from d-glucuronic acid for oxidized and epimerized amylose by 2D NOESY and COSY+1H NMR.