Fig. 4

Tandem MS spectrum of the species displaying a +16 Da mass shift from the unmodified DP4 produced by PaLPMO9H from XXXGXXXG (detected at m/z 645.16). The observed fragments indicate the co-existence of two oxidized forms: a gem-diol at the non-reducing end and an aldonic acid at the reducing end. Observed fragments are depicted on the structures in a and b. Red fragments are specific of the aldonic acid, purple fragments are specific of the gem-diol and blue fragments are common to both oxidized species. Fragments labeled with a star could not be attributed to either expected structures. Their masses match with an oxidation at one laterally branched xylose residue, which origin remains undetermined