Scheme 1.
In vivo and in vitro oxidizing systems required for MDH activity. (A) Physiological pathway for electron flow from methanol to cytochrome cH in Ca- and Ln-dependent MDHs, and the protein-linked assay system for MDH activity measurements. Electron transfer from XoxG to cytochrome cH is assumed based on analogy to MxaG but has not yet been demonstrated in vitro. The in vitro assay monitors cytochrome c reduction at 550 nm. The M. extorquens XoxG reduction potential (Em) is determined in the present work. (B) Dye-linked assay system for MDH activity measurements, adapted from ref. [8d]. The assay monitors DCPIP reduction at 600 nm.