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Reduction of cells or extracts of Nitrosomonas europaea with dithionite leads to a peak in absorption spectra at 460 nm. Most of this chromophore is bound to hydroxylamine oxidase, but a small fraction exists as a separate protein, namely cytochrome P-460. An improved purification of both these proteins is described. The mobility of cytochrome P-460 on gel electrophoresis in the presence of SDS corresponded to a molecular weight of 18000, whereas a molecular weight of 52000 was determined by gel filtration. The band obtained by electrophoresis gave a yellow-green fluorescence in UV light. Electrophoresis in the presence of 8 m-urea, or after acid-treatment, resulted in red fluorescence from cytochrome P-460.
We previously reported that extracts from N. europaea gave eight fluorescence bands in SDS-polyacrylamide gels; cytochrome P-460 was found to correspond to the previously unassigned band VI. Electrophoresis of purified hydroxylamine oxidase did not give a band in common with cytochrome P-460. Highly purified cytochrome P-460 gave no detectable flavin-type fluorescence. There was no antigenic similarity between hydroxylamine oxidase and cytochrome P-460.