Quantitative Analysis of Time-Resolved Laue Diffraction Patterns

Abstract

Integration and quantification of time-resolved Laue images poses problems beyond those encountered with static Laue images. The flexible analytical profile-fitting technique [Ren & Moffat (1995). J. Appl. Cryst. 28, 461–481] has been extended to handle the integration of multiple-spot images with two or more exposures at different time points superimposed on a single detector flame but displaced by a small shift. Each Lane pattern on a multiple-spot image can be integrated separately; possible spatial overlaps between adjacent spots from either the same or different exposures can be resolved; streakiness and streakiness anisotropy are allowed to be different for each time point. Various strategies for time-resolved Lane diffraction data collection and processing are compared. Time-resolved Lane images obtained during the relaxation of photoactive yellow protein (PYP) from its photostationary state have been processed by the Laue data reduction package LaueView. Continuous laser illumination of PYP crystals establishes a photostationary state and termination of laser illumination starts a relaxation process. However, PYP crystals at the photostationary state are more anisotropically mosaic than those at the ground state, and the mosaicity and its anisotropy vary during the relaxation. Accurate integration of elongated and spatially overlapping spots therefore becomes more difficult. Two data processing strategies have been applied to calculate time-dependent difference Fourier maps of PYP. The first route takes advantage of both the wavelength normalization and the harmonic deconvolution [Ren & Moffat (I 995). J. Appl. Cryst. 28, 461–481, 482–493] algorithms. The second is the method of relative percentage changes of structure-factor amplitudes.