HPLC analysis of oxidized products generated by CelS2 and PcGH61D. The main peaks represent aldonic acids of varying chain length (DP, degree of polymerization), as indicated. These soluble products are generated when the same cellulose chain is cut twice by the enzyme, and when the number of sugar units in between the cleavage sites is sufficiently low (longer oligomers are not soluble). The resulting oligomeric products have normal non-reducing ends and are oxidized at the other end. The color coding is as follows: Phosphoric acid swollen cellulose + Pc GH61D (black), Avicel + Pc GH61D (red), Cellulose nanofibrils + Pc GH61D (magenta), and Avicel + CelS2 (blue). Note that the enzymes also produce small amounts of native oligomers [9, 17] (not shown in figure). This is most likely the result of a chain being cleaved close to an already existing reducing chain end. It can, however, not be completely excluded that cleavage without oxidation (i.e. normal hydrolysis) occurs under certain conditions. Figure taken from Westereng et al., 2011 .