Cytochrome c-557 (551) was prepared from Alcaligenes faecalis. The molecular weight was 65, 000. The haem groups were not split off by the ordinary acid-acetone treatment and, in the presence of pyridine, a normal c-type haemochrome was formed. The cytochrome was found to be a dihaem protein. The reduced form of this cytochrome reacted with CO and the oxidized one with cyanide at pH 7. 2. A two-haem cytochrome (cytochrome cd) was crystallized from the same organism. The molecular weight was 90, 000. This cytochrome contained a c-type haem and a d-like haem, and two atoms of iron per molecule. The c-haem seems to be responsible for its typical α peak with a shoulder. The d-like haem reacted with CO, CN-, NO2and NO under different conditions. Cytochrome cd had a strong nitrite reductase activity. 3. This microorganism had a strong denitrifying activity in anaerobic condition. The cytochrome c-557 (551) was present in the cells grown in the absence of nitrate and nitrite, whereas the cytochrome cd and a small quantity of cytochrome c-557 (551) were present in the cells grown in the presence of nitrate or nitrite. Both cytochromes were absent in the cells grown under high aeration.
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Iwasaki et al. (1971) studied this question.