Sequence of electron carriers in the process of methanol oxidation by a new obligate methylotrophic bacterium

From pink soluble fractions prepared from cells cultured in a copper-free medium, active methanol dehydrogenase (MDH) and two soluble c-type cytochromes (c-I and c-II) were purified homogeneously. The green fractions from cells grown on a medium containing 1.0 mg/l of copper had inactive MDH, cytochrome c-II, and blue copper protein. The amount of copper retained in the blue copper protein increased with cultivation time. The oxidized blue copper protein was similar to the classical type I blue copper proteins since it had the novel absorption peak at 625 nm. However, when the blue protein was reduced with MDH or dithionite, it showed the same spectrum as ferrocytochrome c-I. The isoelectric points of cytochrome c-I, blue copper protein and cytochrome c-II were 9.08, 9.08 and 6.52, respectively. These results suggest that the identity of the purified blue copper protein is cytochrome c-I, and copper ions bind to the cytochrome as methanol is depleted in the culture medium. In addition, MDH activity was not detected at all in the methanol-depleted condition. The data suggest that blue copper protein acts as a negative regulator for MDH. The electrons were transferred as follows: MDH-->cytochrome c-II-->cytochrome c-I (blue copper protein). It was also revealed that the initial 'docking' of MDH and cytochrome c-II is accompanied by electrostatic interactions between lysine or arginine residues on the alpha-subunit of MDH and carboxyl groups on the cytochrome c-II.