Biological EXAFS experiments are usually carried out on frozen samples in order to minimize radiation damage.This causes difficulties when studies at different pH are made, since the pH cannot be measured directly for the frozen sample.We have carried out EXAFS studies of Human Carbonic Anhydrase, a zinc metalloenzyme, at room temperature using a rastering technique to move the X-ray beam across the sample and so minimize radiation damage.The catalytic activity of this enzyme is strongly dependent on the pH and so samples in solutions with different pH values were investigated to determine any structural changes which may occur.The analysis used restrained refinement with full inclusion of multiple scattering.The structural changes observed with varying pH are very small.
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Amiss et al. (1999) studied this question.