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Figure 3
Single-crystal UV–Vis spectroscopic data and X-ray structure of DtpA. (a) UV–visible spectra of a DtpA crystal at 100 K. The initial spectrum (blue) is most consistent with a ferric haem state (Table 1[link]), which is reduced following measurement of the first (orange) and second (red) crystallographic data sets. (b) Reduction of the haem followed in small dose (kGy) increments. The starting ferric spectrum in shown in blue, with progressive reduction after 1.2, 2.4, 3.7, 4.9, 6.1, 7.3, 9.7 and 12.2 kGy dose exposure shown in black and the last spectrum after 14.6 kGy shown in magenta. (c) Spectroscopically validated crystal structure of the oxyferrous form of DtpA (the haem site of monomer A; 2FoFc electron density contoured at 1σ). Online UV–Vis spectra were measured before and after collection of the data set, shown in orange and red, respectively, in (a). (d) Proportion of protein in the ferrous state as a function of accumulated dose. Data points were fitted to an exponential function. (e) UV–visible spectrum of a peroxide-treated DtpA crystal (magenta) compared with a ferric crystal spectrum (blue). The spectrum of the peroxide-treated crystal following X-­ray exposure is shown in orange.

Volume 4| Part 3| May 2017| Pages 263-270
ISSN: 2052-2525