Fig. 6

¹H-NMR analyses of the final oligosaccharide products of alginate digested by AlyPB1. a ¹H-NMR (600 MHz) spectra of the main final products UDP2–UDP6 obtained from sodium alginate digested by AlyPB1. b ¹H-NMR (600 MHz) spectra of the intermediate oligosaccharide products of UDP4 and UDP5 digested by exo-lyase AlyPB2. The intermediate oligosaccharide products UDP3–UDP4, and UDP3–UDP5 and UDP4–UDP5 were individually prepared from the partial digestion of UDP4 and UDP5 by AlyPB2. UDP3–UDP4 represents unsaturated trisaccharides from the final product UDP4; UDP3–UDP5 and UDP4–UDP5 represents unsaturated tri- and tetrasaccharides from the final product UDP5. The most relevant signals are pointed out as follows: the H-4Δ signals at 5.71 or 5.67 ppm indicate that the neighbor to the unsaturated residue (Δ unit) is a G, meaning that ΔG is the first two residues at the non-reducing ends of unsaturated oligosaccharide products. The H-4Δ signals at 5.61 ppm and 5.56 ppm indicate that ΔM is the first two residues at the non-reducing ends. The appearance of a characteristic doublet at 4.71 ppm with ³J_HH = 8.4 Hz corresponds to the β-anomeric proton of a G residue at the reducing end and the single peak occurs at 4.70–4.80 ppm corresponds to β-anomeric proton of a M residue at the reducing end