FIGURE 3.

LC/MS detection of the oxygenated products from (a) Leu-Enk (YGGFL), (b) YG, and (c) GY. Samples were incubated with HRP, acetaldehyde, and XO as described under “Experimental Procedures”; chromatography conditions are described under supplementary Methods. Bottom chromatograms represent the native peptides, top chromatograms the monoxide and dioxide derivatives, all obtained by extraction from the total ion chromatograms. The peaks with dashed lines correspond to reactions carried out in the presence of SOD. SOD also inhibited dioxide and monoxide formation with the other peptides. Dioxide and monoxide species were also detected for Endo2 (YPFF) under similar conditions using selective ion monitoring.