Guanidine Hydrochloride-Induced Changes of the E2 Inner Core of the Bacillus stearothermophilus Pyruvate Dehydrogenase Complex1

The limited proteolysis of the Bacillus stearothermophilus pyruvate dehydrogenase complex by V8 protease yields its core structure solely composed of lipoate acetyltransfer-ase (E2) fragments. The changes in the core with guanidine hydrochloride (GdnHCl) were biphasic: below 0.8 M (first) and above 1.0 M (second) GdnHCl. The changes in the first phase were slight but significant: decreases in ellipticity and light scattering, and an increase in E2 activity. Insignificant changes in the molecular shape and size of the. core were detected on fluorescence spectroscopy, ultracentrifugation, gel filtration, and electron microscopy. On the other hand, the changes in the second phase were drastic; the core was disassembled and denatured. Key words: Bacillus stearothermophilus, denaturation, guanidine hydrochloride, multi-enzyme complex, pyruvate dehydrogenase. A variety of enzyme assemblies are present in a living cell. Even some enzymes isolated in vitro are considered to be assembled in vivo (1). We have been interested in the stabilizing mechanism of a large-scale assembly of poly