X-ray diffraction measurements of dipalmitoylphosphatidylcholine as a function of pressure

A kinetics of azide binding by horseradish peroxidase was studied by temperature-jump method. It was found that the reaction of the enzyme with azide is quite rapid, occuring in microsecond time range. This rate is unusually rapid in contrast to the usual hemoprotein ferric iron-ligand interactions so far reported. The resulting value for the apparent association and dissociation rate constants were k₁=6.8×10⁶ M^?1 s^?1 and k¹=3.5×10⁵ s^?1 at 23°C and pH 5.0 for the reaction. The pH dependence of the rate constants was also studied to show a strong linkage of the ligand binding with a proton uptake of a dissociable group on the enzyme.