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. 2008 Jul 18;283(29):20117–20125. doi: 10.1074/jbc.M800217200

FIGURE 6.

FIGURE 6.

A subpopulation of S. coelicolor FGE C277S does not contain a reduced Cys-272 residue. a, S. coelicolor FGE C277S was labeled with NBD, and adducts were detected by mass spectrometry. Two populations of NBD-modified S. coelicolor FGE C277S were observed. One population corresponds to Cys-272 as a free thiol with a single NBD adduct on Cys-301 (see b and d). The other population had NDB adducts at both Cys-272 and Cys-301 (see c and d). Multiple charge states are shown for both populations. Numbers above each ion peak indicate the number of NBD adducts attributed to each population. b–d, NBD adducts were mapped to each surface-exposed thiol using mass spectrometry after trypsinolysis. Shown are the +2 charge state ions corresponding to Cys-272 as a free thiol (b, calculated mass, 1,457.61; observed mass, 1,457.60), Cys-272 with an NBD adduct (c, calculated mass, 1,620.62; observed mass, 1,620.60), and Cys-301 with an NBD adduct (d, calculated mass, 1,486.54; observed mass, 1486.54). e, Cys-301 was not observed as a free thiol (expected position of +2 charge state ion shown). Cys-301 was an additional surface-exposed thiol that served as an internal control to assess labeling efficiency.