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Figure S1. Composition analysis of the bovine OS-PP-Dol library. Duplicate OST assays containing 60 fmol of purified yeast OST, 500 pmol Nα-Ac-N-[125I]Y-T-NH2, and 15 pmol of a bovine OS-PP-Dol preparation were incubated at 25°C for 72 h in the presence of glucosidase and mannosidase inhibitors. Previously, we have shown that the yeast OST remains active during the 72-h incubation and that the OS-PP-Dol is quantitatively converted into glycopeptides (Kelleher et al., 2001). (A) Glycopeptide products were resolved as a function of the number of saccharide residues by HPLC. One of two HPLC profiles is shown. (B) The oligosaccharide composition (presented as a percentage) of the heterogeneous bovine OS-PP-Dol library was obtained by averaging two determinations. The heterogeneity of the OS-PP-Dol library is explained by exposure of the OS-PP-Dol to mannosidases and glucosidases before solvent extraction during the isolation of OS-PP-Dol from bovine pancreas (Kelleher et al., 2001).