The quinoprotein methanol dehydrogenase and cytochrome c-551i form a physiologic complex in which electrons are transferred from pyrroloquinoline quinone to heme. The reoxidation of methanol dehydrogenase by the cytochrome was studied by stopped-flow spectroscopy. The rate constant for the electron transfer reaction and the dissociation constant for complex formation were each determined at temperatures ranging from 20 to 50°C. The electron transfer rates varied from 1.4 to 4.6 s-1. Analysis of the electron transfer reaction by Marcus theory yielded values of 1.9 eV for the reorganizational energy and 0.071 cm-1 for the electronic coupling and predicted a theoretical distance between redox centers of 15 Å. Kinetically determined dissociation constants correlated well with a Kd of 375 μM which was determined in a direct ultrafiltration binding assay. Thermodynamic analysis of the dissociation constants indicated the importance of the hydrophobic effect in complex formation.
ASJC Scopus subject areas