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. Author manuscript; available in PMC: 2010 Apr 6.
Published in final edited form as: J Biol Chem. 2006 Dec 28;282(9):5984–5990. doi: 10.1074/jbc.M608087200

Figure 4. Assay of recombinant human xylosyltransferase II expressed in mammalian and yeast systems using the bikunin peptide.

Figure 4

Xylosyltransferase activity of concentrated supernatants of either (A) pgsA-745 or (B) Pichia transformed with vectors encoding XT-II was measured overnight at 37 °C using the bikunin peptide substrate in the presence of UDP-Xyl, HEPES buffer, pH 8, and Mn(II). Controls with either (C) Pichia-expressed XT-II incubated in the absence of UDP-Xyl or of (D) Pichia transformed with empty vector were also performed. The primary xylosylation product has an m/z of 1322. In all cases, a secondary reaction resulting in a shift in m/z of −17 (species of 1173 and 1305) was also, as previously described (Ref. 19), observed and is presumed to be due to the conversion of the N-terminal glutamine residue of both the acceptor and product to pyroglutamate; this modification has no obvious effect on the xylosyltransferase reaction.