Competitive Interaction of Component Enzymes with the Peripheral Subunit-Binding Domain of the Pyruvate Dehydrogenase Multienzyme Complex of Bacillus stearothermophilus: Kinetic Analysis Using Surface Plasmon Resonance Detection†

The interactions of the peripheral enzymes (E1, a pyruvate decarboxylase, and E3, dihydrolipoyl dehydrogenase) with the core component (E2, dihydrolipoyl acetyltransferase) of the pyruvate dehydrogenase (PDH) multienzyme complex of Bacillus stearothermophilus have been analyzed using a biosensor based on surface plasmon resonance detection. A recombinant di-domain (lipoyl domain plus peripheral subunit-binding domain) from E2 was attached to the biosensor chip by means of the pendant lipoyl group. The dissociation constant (Kd) for the complex between the peripheral subunit-binding domain and E3 (5.8 × 10-10 M) was found to be almost twice that for the complex with E1 (3.24 × 10-10 M). This was due to differences in the rate constants for dissociation (kdiss); these were 1.06 × 10-3 and 1.87 × 10-3 s-1 for the complexes with E1 and E3, respectively, whereas the rate constants for association (kass) were identical (3.26 × 106 M-1 s-1). Separate studies using non-denaturing polyacrylamide gel electrophoresi...