was grown in oxygen-limited continuous culture in a lactate/tryptone/yeast extract medium containing 7·5 μg haematin ml. Low temperature difference spectra of whole organisms and washed membranes showed two peaks in the cytochrome region, at 558 nm and 562 nm, and a peak at 627 nm indicative of a -type cytochrome. A CO-binding cytochrome was also present in the haematin-grown bacteria. These cytochromes were not detected in bacteria grown without haematin. The haematin- grown bacteria produced proton pulses in a weakly buffered medium when pulsed with oxygen-saturated buffer. The average →H+/O ratio of such pulses was 1·4 and they were abolished by carbonyl cyanide m-chlorophenylhydrazone (CCCP). The haematin-grown bacteria had a high activity of particulate NADH oxidase, at least 10 times that of bacteria grown without haematin. They also had a high lactate which was strongly inhibited by CCCP and gramicidin whereas bacteria grown without haematin had a very low lactate largely insensitive to the uncoupling agents. The glucose was similar in bacteria grown in the presence or absence of haematin but was stimulated by uncoupling agents in haematin- grown organisms and slightly inhibited by these agents in organisms grown without haematin. These results confirm earlier findings of the ability of to form a functional cytochrome system in the cell membrane when supplied with haematin and show that electron transport to oxygen by such a system is coupled to proton translocation.


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