On the Conformation of NADP-dependent Isocitrate Dehydrogenase fromBascillus stearothermophilus

Abstract

Measurements of the optical rotatory dispersion and circular dichroism of NADP-dependent isocitrate dehydrogenase [EC 1.1.1.42] from B. stearothermophilus revealed the presence of about 30% α-helical structure in the molecule. In the presence of substrate, the optical activity properties differed from those of the native enzyme alone, suggesting a slight decrease of α-helical conformation in the enzyme. Under denaturing conditions (thermal or 8M urea treatment), the substrate protected the enzyme molecule from denaturation. These results suggested that the interaction of substrate with the enzyme enhanced the stability of the enzyme.