Macromolecular crystallography on the millisecond to nanosecond time domain

Successful time-resolved x-ray crystallography depends on the rapid, uniform, non-damaging initiation of a structural reaction in a single crystal of excellent diffraction quality; on the ability to monitor the course of the reaction by the change in x-ray structure amplitudes in real time; and on the analysis of the changes in electron density in terms of time-independent structures of reactants, intermediates, and products. The process is greatly aided if there is an independent measure of the reaction coordinate afforded by, for example, the optical density of the crustal; and may be hindered by artifacts, some of which are thermal in origin, which degrade the x-ray diffraction patterns. Recent results which utilize multiple bunches emitted by a synchrotron source on the millisecond time domain, or a single bunch on the sub-nanosecond time domain, will be presented for several protein crystals in which the structural reaction can be initiated by light.