Journal Article Research Support, N.I.H., Extramural Proteins Research Support, U.S. Gov't, Non-P.H.S. 3352-57-6 Hydroxyl Radical mass spectrometry 059QF0KO0R 9007-43-6 Cytochromes c Nucleic Acids Oxygen RNA, Catalytic RNA, Protozoan Research Support, Non-U.S. Gov't S88TT14065 Solutions Water X-ray footprinting mass spectrometry (XFMS) X-rays beamlines bound water footprinting hydroxyl radical hydroxyl radical labeling microsecond irradiation protein conformation protein modification protein structure radiation damage