The reactivity of galactose oxidase with snail galactans, galactosides and D-galactose-composed oligosaccharides.
The enzymic oxidation of snail galactans, of their first and second Smith degradation products and of some structurally related polysaccharides was studied. Lymnaea stagnalis galactan after one cycle of Smith degradation reacted best and native Helix pomatia galactan was almost inactive. Investigations on the structural requirements for oligosaccharides to bind to galactose oxidase showed that the branched tetrasaccharide, Gal-beta-1----6-[Gal-beta-1----3]-Gal-beta-1----1 L-Gro, in the terminal nonreducing position was the most complementary structure in the native galactan to associate with the enzyme. All nitrophenyl alpha-galactosides reacted better, and the ortho-form was 10-times more potent compared with this tetrasaccharide, indicative of the involvement of a hydrophobic region in binding. However, the beta-linked isomers were only equally or less reactive than galactose. The enzymic oxidation determined colorimetrically by transferring the peroxide formed to o-dianisidine ceased at a maximum typical for each substrate and independent of the reaction time. When the absolute turn-over rates for ortho- and para-nitrophenyl alpha-galactoside and for the beta-isomer were determined by HPLC, it could be demonstrated that the oxidation had not finished at the maximum of the colour reaction, but proceeded until the substrate was consumed. The initial speed of the colour reaction paralleled the absolute oxidation rate.
D000818:Animals; D005685:Galactans / Q000378:metabolism*; D005692:Galactose Oxidase / Q000378:metabolism*; D005697:Galactosides / Q000378:metabolism*; D006027:Glycosides / Q000378:metabolism*; D006372:Helix, Snails; D007700:Kinetics; D008195:Lymnaea; D009844:Oligosaccharides / Q000378:metabolism*; D010084:Oxidation-Reduction; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D005685:Galactans; D005697:Galactosides; D006027:Glycosides; D009844:Oligosaccharides; D005692:Galactose Oxidase