Figure 5

MALDI-TOF MS spectra of xylan-RAC mixtures incubated with MtLPMO9A. b Birchwood xylan (BiWX; 2 mg mL⁻¹) and c oat spelt xylan (OSX; 2 mg mL⁻¹) in the presence of regenerated amorphous cellulose (RAC; 2 mg mL⁻¹) after incubation of MtLPMO9A (10 mg g⁻¹ substrate). Samples were incubated in a 50 mM ammonium acetate buffer (pH 5.0) for 24 h at 52°C with ascorbic acid addition (1 mM). MtLPMO9A incubation of BiWX and OSX with RAC addition releases non-oxidized and oxidized xylo- and gluco-oligosaccharides (XOS_n, XOS ^#_n *; GlcOS_n, GluOS ^#_n *). The presence of C4-oxidized XOS_n*, and XOS ^#_n oxidized at C1 to an aldonic acid (^# + 16 Da) is shown. Non-oxidized GlcOS_n and oxidized GlcOS ^#_n * are less detectable due to abundance of xylo-oligosaccharides present. From BiWX also 4-O-methylglucoronic acid containing non-oxidized XOS_n (GlcA_meXOS_n) and 4-O-methylglucoronic acid containing oxidized XOS ^#_n * (GlcA_meXOS ^#_n *) are formed. a Illustrated structure of 4-O-methylglucoronic acid containing C1- and C4-oxidized XOS_n.(GlcA_meXOS ^#_n , GlcA_meXOS_n*, respectively). Masses represent lithium adducts only. Double Li adducts are determined for C1-oxidized products (^§ + 6 Da). MALDI-TOF MS analysis of BiWX and OSX in the presence of RAC after incubation of MtLPMO9A without ascorbic acid did not reveal detectable amounts of oxidized products (data not shown).