10. ELECTRON TRANSPORT AND OXIDATIVE PHOSPHORYLATION
457
components, the greatest amount of information available relates to the
occurrence of the cytochromes. The broad distribution of the cytochromes was first indicated by Keilin's studies (5). His work showed
that the cytochromes were present not only in animal tissues, as MacMunn (4) had recognized, but were also present in yeast, insects,
higher plants, and aerobic bacteria. Recently even the exceptions cited
by Keilin, the anaerobic bacteria, have been shown to contain cytochromes. Thus a cytochrome of the c type was found in Chlorobium
limicola, an obligate anaerobe and photoautotroph (117). Postgate
(118) has purified a cytochrome with an unusually low oxidation-reduction potential (E 0 = —0.205, pH 7.0) from Desulfovibrio
desulfuricans,
a strict anaerobe. A sample of cytochrome, possibly containing several
heme-proteins, was isolated from an obligate photosynthetic anaerobe,
Chromatium (119). This protein fraction has properties similar to plant
cytochrome f and to mammalian cytochromes c and b. Kamen and
Vernon (120) have examined the cytochromes present in the nonsulfur
purple bacteria and Vernon has isolated and partially purified cytochromes from the denitrifiers, Micrococcus denitrificans and Pseudomonas denitrificans (121). Of interest is the fact that Streptococcus
faecalis (16, 122) and Clostridium pasteurianum (123) contain no
hematin compounds. Instead, Dolin has shown the presence of flavoproteins capable of oxidizing DPNH by 0 2 in S. faecalis (124).
In earlier work, cytochromes had been recorded among the fungi in
Neurospora crassa (125), Penicillium notatum (125), Ustilago sp. (126),
Myrothecium verrucaria (127), and Aspergillus sp. (128). In a late report, the absorption bands of cytochrome were detected in the mycelia
of 45 fungal species by direct observation with a hand spectroscope
(129).
The plant cytochromes have been the subject of a recent review
(15). The distribution of pigments is broad. With plants, however, there
is some reason to believe that certain of the cytochromes perform unique
functions in addition to their role in respiration. Thus, Lundegardh
(130) has proposed a scheme for ion absorption which is intimately
associated with cytochromes a 3 , a, c, and b of the respiratory chain. In
addition, Hill and Hartree (131) have commented on the possibility
that a new cytochrome, cytochrome f, which is present in high concentration in chloroplasts, may participate in photosynthesis. Recently the
photooxidation of cytochrome c (132) has been observed in chloroplasts.
Because ferrocytochrome f is oxidized by ferricytocrirome c, this constitutes a mechanism for linking the reducing power of ferrocytochrome
f to the reduction of the oxidizing component ("OH") formed in the
photolysis of H 2 0. Two other plant pigments, cytochromes b 3 and b 7 ,
457
components, the greatest amount of information available relates to the
occurrence of the cytochromes. The broad distribution of the cytochromes was first indicated by Keilin's studies (5). His work showed
that the cytochromes were present not only in animal tissues, as MacMunn (4) had recognized, but were also present in yeast, insects,
higher plants, and aerobic bacteria. Recently even the exceptions cited
by Keilin, the anaerobic bacteria, have been shown to contain cytochromes. Thus a cytochrome of the c type was found in Chlorobium
limicola, an obligate anaerobe and photoautotroph (117). Postgate
(118) has purified a cytochrome with an unusually low oxidation-reduction potential (E 0 = —0.205, pH 7.0) from Desulfovibrio
desulfuricans,
a strict anaerobe. A sample of cytochrome, possibly containing several
heme-proteins, was isolated from an obligate photosynthetic anaerobe,
Chromatium (119). This protein fraction has properties similar to plant
cytochrome f and to mammalian cytochromes c and b. Kamen and
Vernon (120) have examined the cytochromes present in the nonsulfur
purple bacteria and Vernon has isolated and partially purified cytochromes from the denitrifiers, Micrococcus denitrificans and Pseudomonas denitrificans (121). Of interest is the fact that Streptococcus
faecalis (16, 122) and Clostridium pasteurianum (123) contain no
hematin compounds. Instead, Dolin has shown the presence of flavoproteins capable of oxidizing DPNH by 0 2 in S. faecalis (124).
In earlier work, cytochromes had been recorded among the fungi in
Neurospora crassa (125), Penicillium notatum (125), Ustilago sp. (126),
Myrothecium verrucaria (127), and Aspergillus sp. (128). In a late report, the absorption bands of cytochrome were detected in the mycelia
of 45 fungal species by direct observation with a hand spectroscope
(129).
The plant cytochromes have been the subject of a recent review
(15). The distribution of pigments is broad. With plants, however, there
is some reason to believe that certain of the cytochromes perform unique
functions in addition to their role in respiration. Thus, Lundegardh
(130) has proposed a scheme for ion absorption which is intimately
associated with cytochromes a 3 , a, c, and b of the respiratory chain. In
addition, Hill and Hartree (131) have commented on the possibility
that a new cytochrome, cytochrome f, which is present in high concentration in chloroplasts, may participate in photosynthesis. Recently the
photooxidation of cytochrome c (132) has been observed in chloroplasts.
Because ferrocytochrome f is oxidized by ferricytocrirome c, this constitutes a mechanism for linking the reducing power of ferrocytochrome
f to the reduction of the oxidizing component ("OH") formed in the
photolysis of H 2 0. Two other plant pigments, cytochromes b 3 and b 7 ,