Fig. 4
From: Role of surface tryptophan for peroxidase oxidation of nonphenolic lignin
HSQC NMR spectra of softwood (a–c) and hardwood (d–f) lignosulfonates treated for 24 h with native VP (b, e) and its W164S variant (c, f) and control without enzyme (a, d), and formulae of the main structures identified (g). Signals correspond to 13C-1H correlations at the different positions of lignin native/α-oxidized/α-sulfonated syringyl (red signals) and guaiacyl (green signals) units, α-sulfonated/non-sulfonated side chains in β-O-4′ (blue signals), phenylcoumaran (cyan signals), and resinol (purple signals) substructures, and methoxyls (orange signal) (gray, unassigned signals). Same amount of sample (40 mg before enzymatic treatment) and DMSO-d 6 (0.75 mL) were used for all the spectra, which were normalized to the same intensity of the DMSO signal (not shown) for comparison. List of signals (δC/δH ppm): 53.2/3.46, Cβ/Hβ in phenylcoumarans (B β ); 53.4/3.00, Cβ/Hβ in resinols (C β ); 55.5/3.66, C/H in methoxyls (MeO); 59.4/3.4 and 3.72, Cγ/Hγ in β–O–4′ (A γ ); 61.1/4.00, Cγ/Hγ in sulfonated β–O–4´ (A γ ); 65.6/3.93, Cα/Hα in sulfonated β–O–4′ linked to a G-unit (A α(G) ); 67.2/4.02, Cα/Hα in sulfonated β–O–4′ linked to a S-unit (A α(S) ); 70.8/4.16 and 3.77, Cγ/Hγ in β-β′ resinols (C γ ); 71.1/4.72, Cα/Hα in β–O–4′ linked to a G-unit (A α(G) ); 71.5/4.85, Cα/Hα in β–O–4′ linked to a S-unit (A α(S) ); 79.3/4.91, Cβ/Hβ in sulfonated β–O–4′ linked to a G unit (A β(G) ); 80.9/4.67, Cβ/Hβ in sulfonated β–O–4′ linked to a S unit (A β(S) ); 83.3/4.24, Cβ/Hβ in β–O–4′ linked to a G unit (A β(G) ); 84.9/4.59, Cα/Hα in β-β′ resinols (C α ); 85.7/4.08, Cβ/Hβ in β–O–4′ linked to a S unit (A β(S) ); 86.7/5.41, Cα/Hα in phenylcoumarans (B α ); 103.8/6.68, C2/H2 and C6/H6 in syringyl units (S 2,6 ); 106.2/7.29, C2/H2 and C6/H6 in α-oxidized syringyl units (S’ 2,6 ); 108.0/6.68, C2/H2 and C6/H6 in sulfonated syringyl units (S 2,6 ); 114.0/6.60 and 114.3/6.87, C2/H2 and C5/H5 in guaiacyl units (G 2 /G 5 ); and 122.8/6.75, C6/H6 in guaiacyl units (G 6 ) (minor, and largely overlapping, signals of C2/H2, C5/H5 and C6/H6 correlations in non-sulfonated guaiacyl units would appear at 110.7/6.93, 114.2/6.65 and 118.6/6.79 ppm, respectively; not shown). Three additional aromatic signals in the treated samples, at 126.1/7.14, 127.7/7.21 and 128.9/7.22 ppm, were assigned to protein (phenylalanine residues in the added enzyme)