Purification and properties of a 'cytochrome a1'-like hemoprotein from a magnetotactic bacterium, Aquaspirillum magnetotacticum.

A novel hemoprotein was purified from a magnetotactic bacterium, Aquaspirillum magnetotacticum MS-1. The protein showed absorption peaks at 437 nm in the oxidized form, and 592, 550 and 450 nm in the reduced form. Although the spectral properties of the hemoprotein were very similar to those of 'cytochrome a1', the hemoprotein contained no molecules of heme a. The protein contained two kinds of hemes; one was extracted with HCl-acetone and the other was covalently bound to the protein. The pyridine ferrohemochrome of the former heme showed absorption peaks at 440, 545 and 585 nm. The chromatographic behavior of the heme on reverse-phase HPLC was different from that of heme a. The pyridine ferrohemochrome of the covalently bound heme showed an alpha peak at 565 nm. On the basis of the iron analysis, the hemoprotein contained one molecule of each of the two kinds of heme in the holoprotein. The protein was composed of two kinds of subunit with molecular weights of 41,000 and 17,000 and showed very little cytochrome c oxidase activity. The amounts of the hemoprotein in the magnetic cells of A. magnetotacticum were larger than those in non-magnetic cells. These results suggest that the 'cytochrome a1'-like hemoprotein is not the terminal oxidase of the bacterium and may be related to the formation of magnetosome in the magnetic cells of A. magnetotacticum.