GUANIDINE HYDROCHLORIDE-INDUCED CHANGES OF THE E2 INNER-CORE OF THE BACILLUS-STEAROTHERMOPHILUS PYRUVATE-DEHYDROGENASE COMPLEX

The limited proteolysis of the Bacillus stearothermophilus pyruvate de hydrogenase complex by V8 protease yields its core structure solely co mposed of lipoate acetyltransferase (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 pha se were slight but significant: decreases in ellipticity and light sca ttering, and an increase in E2 activity, Insignificant changes in the molecular shape and size of the; core were detected on fluorescence sp ectroscopy, ultracentrifugation, gel filtration, and electron microsco py. On the other hand, the changes in the second phase were drastic; t he core was disassembled and denatured.