Figure 3

Activity of MtLPMO9A on amorphous cellulose. a Structure and nomenclature used: XOS_n and GlcOS_n, non-oxidized xylo- and gluco-oligosaccharides; XOS ^#_n and GlcOS ^#_n , xylo- and gluco-oligosaccharides oxidized at the C1 carbon atom; XOS_n* and GlcOS_n*, xylo- and gluco-oligosaccharides oxidized at the C4 carbon atom. b HPAEC elution pattern of regenerated amorphous cellulose (RAC) after incubation with MtLPMO9A (5 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). In the presence of ascorbic acid, oxidized GlcOS ^#_n * are formed by MtLPMO9A (marked either with ^# or *), of which the masses were analyzed by MALDI-TOF MS. Using RAC as a substrate, small amounts of non-oxidized XOS_n are detected by HPAEC. c MALDI-TOF mass spectrum of RAC incubated with MtLPMO9A with ascorbic acid. Clusters of oxidized GlcOS ^#_n * are determined as their lithium (Li) adducts. The insert shows masses of XOS ^#_n * and GlcOS ^#_n * oxidized either at C4 leading to a keto-group (* −2 Da) or C1 leading to a lactone (^# −2 Da). The δ-lactones are unstable in water and hydrolyse to the corresponding aldonic acids (^# +16 Da). Double Li adducts (one Li adduct and one additional Li exchanged for H on the acid group) are C1-oxidized products (^§).