Summary of the oxidative cleavage of cellulose. In the case of cleavage by CelS2, a CBM33, and Pc GH61D  the only oxidized sugars observed are aldonic acids, as indicated in this figure. Other members of the GH61 family seem to generate additional oxidized species, with oxidation at C4 or C6 (see Quinlan et al.  and Phillips et al.  for further discussion).