THE INTERACTION OF METHANOL DEHYDROGENASE AND ITS ELECTRON-ACCEPTOR, CYTOCHROME-CL IN METHYLOTROPHIC BACTERIA

The interactions of methanol dehydrogenase (MDH, EC1.1.99.8) with its specific electron acceptor cytochrome c(L) has been investigated in Methylobacterium extorquens and Methylophilus methylotrophus. The MDHs of these two very different methylotrophs have the same alpha-2-beta-2 structure; the interaction of these MDHs with their specific electron acceptor, cytochrome c(L), has been studied using a novel assay system. Electrostatic reactions are involved in 'docking' of the two proteins. EDTA inhibits the reaction by a process involving neither metal chelation nor the 'docking' process. Chemical modification studies showed that the two proteins interact by a 'docking' process involving interactions of lysyl residues on MDH and carboxyl residues on cytochrome c(L). When 'zero length', two stage cross-linking was done (with proteins from both bacteria), the alpha-subunits of MDH cross-linked with cytochrome c(L) by way of lysyl groups on MDH and carboxyl groups on the cytochrome. Tuna mitochondrial cytochrome c provided a model for cytochrome c(H) which is the electron acceptor for cytochrome c(L) in the 'methanol oxidase' electron transport chain. Tuna cytochrome c was shown to form crosslinked products with carboxyl-modified cytochrome c(L). MDH and tuna cytochrome c competed for the same domain on cytochrome c(L). It was concluded that MDH reacts with cytochrome c(L) by an electrostatic reaction which involves carboxyl groups on cytochrome c(L) and amino groups on the alpha-subunit of MDH. The same domain on cytochrome c(L) is involved in subsequent 'docking' with its electron acceptor.