Fig. 1.

Pictorial representation of modification sites on cyt c (A and B) and ubiquitin (C and D) in two orientations. Colored surface representation based on the X-ray crystal structure of cyt c (1HRC) (27) and ubiquitin (1UBQ) (28) indicate the side-chain residues that are consistently modified after irradiation under RT and/or frozen conditions. Blue indicates the residues that show 13- to 200-fold decreases in modification upon freezing, violet indicates 3- to 10-fold decreases, and red indicates minimal to no change (< 2-fold) in the modification rate when sample is frozen compared to RT. Y67 in cyt c is completely buried inside the heme cavity and not visible in these orientations.