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. Author manuscript; available in PMC: 2008 Oct 13.
Published in final edited form as: Biochemistry. 2006 Jan 17;45(2):552–560. doi: 10.1021/bi051862l

FIGURE 5.

FIGURE 5

1H-NMR analysis of alginate samples obtained after partial to exhaustive epimerization of poly-D-mannuronan by P. aeruginosa C5-mannuronan epimerase. Assay conditions are discussed in the text. Spectra were recorded at 500 MHz and 80 °C in D2O. Peak assignments are indicated on panels C and D. Numbers designate the position of the H-atom in the hexose ring; the underlined letters (M and G) denote the residue that is giving rise to the indicated peak, while the letters that are not underlined specify neighboring residues in the linear polymer. Peaks labeled by asterisks are due to 13C coupling to MM-1 protons. (A) Spectrum of poly-D-mannuronan (FG = 0, FM = 1, dpaverage = 93) used as starting material in the assay. (B) Heteropolymeric alginate at very low conversion (FG = 0.02, FGG = 0). (C) Heteropolymeric alginate at moderate conversion (FG = 0.26, FGG = 0.06). (D) Heteropolymeric alginate formed as the final product by exhaustive epimerization by C5-mannuronan epimerase (FG = 0.75, FGG = 0.50). The vertical dashed line at 4.95 ppm marks the signal that arises from H-1 on guluronate and serves to indicate the extent of the reaction. The vertical dashed line at 4.40 ppm marks the signal that arises from the C-5 proton of the central guluronate residue in a GGG triad, and indicates the formation of G tracts.