Components of the cytochrome system of Alcaligenes sp. N.C.I.B., 11015, with special reference to particulate bound c-type cytochromes.

1. The cytochrome type of the particulate fraction from cells of Alcaligenes sp. was examined. The particulate fraction of aerobically-grown cells contained b-, c-, a-type and o-type like cytochromes, whereas that from nitrate-grown cells contained b-, c-type and o-type like cytochromes. 2. Two kinds of c-type cytochromes were extracted and purified from the particulate fraction of nitrate-grown cells of Alcaligenes sp. One of them showed absorption maxima at 415.5, 522, and 551 nm is the reduced form, and at 410.5 nm in the oxidized form; the other at 417.5, 523, and 556 nm in the reduced form, and at 412 nm in the oxidized form; these cytochromes were designated cytochrome c-551 and cytochrome c-556, respectively. 3. Cytochrome c-551 had a molecular weight of 28,800 and had two heme groups per molcule. The midpoint oxidation reduction potential at pH 7.0 (Em, 7) was +262 mV. Cytochrome c-556 had a molecular weight of 18,200 and contained one heme group per molecule. The Em, 7 value was +291 mV. These cytochromes were not autoxidizable, did not react with carbon monoxide or KCN at pH 7.0, and were reduced by ascorbate. 4. Each cytochrome acts to some degree as electron carrier in the dissimilatory nitrite reduction reaction of Alcaligenes sp.