Potassium Iodide-Induced Changes in Pyruvate Dehydrogenase Complex from Bacillus stearothermophilus

Treatment with KI and its subsequent removal induced disassembly of Bacillus stearothermophilus pyruvate dehydrogenase complex (PDC) and association of disassembly products, respectively. The disassembly yielded neither completely dissociated components nor aggregate, but did yield a few molecular forms smaller than PDC. Depending on the KI concentration, these changes were of three phases: K-1, below 0.6 M; K-2, 1.0-1.5 M; K-3, above 1.8 M. PDC was disassembled in K-1 to C1 comprising pyruvate decarboxylase and lipoate acetyltransferase mainly and C2 comprising the decarboxylase and dihydrolipoamide dehydrogenase. In K-1, the removal of KI resulted in an apparent reconstitution of PDC. The mixing of C1 with an excess of C2 yielded an assembly larger than PDC and restored enzyme activities, but specific activities were different from those of PDC. In K-2 and K-3 phases, complexes smaller than PDC were yielded from disassembly products, and activities except for that of the acetyltransferase were not restored.