Glutamate dehydrogenase from Clostridium symbiosum has been studied by circular dichroism spectroscopy. The far UV spectrum shows negative bands at 205 nm and 220 nm typical of α-helical structure. Change in the pH from 7 to 8.8 has little effect on this spectrum, suggesting no major change in secondary structure. The near UV spectrum is strongly negative with a maximum at 208 mn, shoulders at 293, 287, 274 and 266 nm and a trough at 258 nm. This spectrum is intensified by about 50% on-going from pH 7 to 8.8 indicating a perturbation of the aromatic chromophores in keeping with the conformational change suggested by the concomitant time-dependent inactivation of the enzyme. The dichroic absorption at 280 nm was used to follow the time course of change from pH 8.8 (inactive) to pH 7 (active). This transition at 30°C was virtually complete in 15 min. The pH dependence of the CD changes suggests a pK of 7.8 for the conformational change.
