The -type cytochrome oxidase from methanol-grown has been solubilized and purified (15-fold) to homogeneity. The pure, active oxidase consisted of equal amounts of -type and -type cytochromes, corresponding to the two types of protein subunit seen on SDS-PAGE; these had molecular weights of 31 500 and 23800, respectively. The active oxidase probably has two cytochrome subunits and two cytochrome subunits, both cytochrome types reacting with CO. The cytochrome subunit did not correspond to either of the two soluble cytochromes from The pure oxidase complex oxidized TMPD very rapidly, having a of 36 μmol O min (mg protein). It was inhibited noncompetitively by azide ( , 1.13 μ) and KCN ( , 0.2 μ), the values being similar to those measured during respiration by whole bacteria.

Of the two soluble cytochromes from , cytochrome was oxidized at 50 times the rate of cytochrome , the turnover number with cytochrome as substrate being 21 s. The cytochrome component of the oxidase was unable to act as electron acceptor from pure methanol dehydrogenase (soluble, or after solubilization from membranes). A complete ‘methanol oxidase’ electron transport chain was reconstituted from completely pure proteins: methanol dehydrogenase, cytochrome and and the cytochrome oxidase complex. This ‘methanol oxidase’ showed the same sensitivity to inhibition as observed during methanol oxidation by whole bacteria.


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