QUANTITATIVE-ANALYSIS OF TIME-RESOLVED LAUE DIFFRACTION PATTERNS

Integration and quantification of time-resolved Laue images poses prob lems beyond those encountered with static Laue images. The flexible an alytical profile-fitting technique [Ren & Moffat (1995). J. Appl. Crys t. 28, 461-481] has been extended to handle the integration of multipl e-spot images with two or more exposures at different time points supe rimposed on a single detector frame but displaced by a small shift. Ea ch Laue 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 a nisotropy are allowed to be different for each time point. Various str ategies for time-resolved Laue diffraction data collection and process ing are compared. Time-resolved Laue images obtained during the relaxa tion of photoactive yellow protein (PYP) from its photostationary stat e have been processed by the Laue data reduction package LaueView. Con tinuous laser illumination of PYP crystals establishes a photostationa ry state and termination of laser illumination starts a relaxation pro cess. However, PYP crystals at the photostationary state are more anis otropically mosaic than those at the ground state, and the mosaicity a nd its anisotropy vary during the relaxation. Accurate integration of elongated and spatially overlapping spots therefore becomes more diffi cult. Two data processing strategies have been applied to calculate ti me-dependent difference Fourier maps of PYP. The first route takes adv antage of both the wavelength normalization and the harmonic deconvolu tion [Ren & Moffat (1995). J. Appl. Cryst. 28, 461-481, 482-493] algor ithms. The second is the method of relative percentage changes of stru cture factor amplitudes.