A circular dichroism study of the pH‐dependent activation/inactivation equilibrium in the glutamate dehydrogenase of <i>Clostridium symbiosum</i>

Abstract

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 p K of 7.8 for the conformational change.