Figure 9. MALDI spectra of the reaction products catalyzed by PtrGXM1, PtrGXM2, PtrGXM3, and PtrGXM4 recombinant proteins.

Purified recombinant PtrGXMs were incubated with the GlcA-substituted Xyl₄ [(GlcA)Xyl₄] acceptor and the S-adenosylmethionine methyl donor and the reaction products were purified and subjected to MALDI analysis. Note the appearance of a new ion peak at m/z 759 corresponding to (MeGlcA)Xyl₄ (red arrows) with an increase of 14 D relative to the (GlcA)Xyl₄ acceptor (m/z 745) in the products of reactions incubated with PtrGXMs but not with MBP. The ions at m/z 767 and 781 are attributed to the doubly sodiated species [M+2Na]⁺ of (GlcA)Xyl₄ and (MeGlcA)Xyl₄, respectively.