478
ERIC E. CONN
Particulate fractions from Peltandra virginica spadix exhibited cytochrome oxidase activity which was inhibited by cyanide and carbon
monoxide (257). This spadix also contained a cytochrome of the b
type which appeared, from difference spectra, to function either in the
presence or absence of cyanide. From these studies Yocum and Hackett
concluded that cytochrome oxidase does function in the respiration of
the aroid spadix. However, to account for the cyanide-insensitive
respiration, Yocum and Hackett favor the view that there is an alternate,
cyanide-resistant pathway of electron transfer to 0 2 which involves a
cytochrome of the b type. Further support for this view is found in the
work of Bendall and Hill (258), who observed that mitochondria from
spadix of Arum maculatum contain a cytochrome (cytochrome b 7 )
which does not react with CO and is oxidized by air in the presence of
103 M HCN.
Cytochrome c oxidase activity of mitochondria from Arum maculaturn (259) and skunk cabbage (Symplocarpus
foetidus)
(260)
spadices is inhibited strongly by cyanide (10
-3 M-10"
4 M). The succinoxidase activity of the same particles is also inhibited, but only to the
extent of 50-60%. These results indicate that succinate oxidation can be
effected by electron transfer in part through cytochrome c to 0 2 , and
this is the amount inhibited by cyanide. However, a cyanide-insensitive
route must also exist in these particles, the nature of which remains unknown. Similar conclusions result from studies on the oxidation of
DPNH by skunk cabbage spadix mitochondria (260). Since the autoxidizable, cyanide-insensitive cytochrome b is' present in these particles,
it is believed to be a component. The question of whether the cyanideresistant pathway can support oxidative phosphorylation has been
raised (257), but no information is available on this subject.
Microsomes of both plant (261) and animal tissues (262, 26S) contain cytochromes of the b type (cytochromes b 3 and b 5 respectively),
and these do not appear to be affected by cyanide. However, the
amount of oxidase activity in microsomes from the aroid spadix appears
insufficient to account for the amount of cyanide-insensitive respiration
which is present in that tissue. Since cytochrome b 3 is found in other
plant tissues (15), its role in respiration in plants needs to be examined
in more detail.
V. Conclusion
As emphasized elsewhere (1), half of the energy-yielding steps encountered in the metabolism of aerobic organisms occur during the
transfer of electrons from the pyridine nucleotides or flavoproteins to
0 2 . At the many different levels of the phylogenetic scale which have
ERIC E. CONN
Particulate fractions from Peltandra virginica spadix exhibited cytochrome oxidase activity which was inhibited by cyanide and carbon
monoxide (257). This spadix also contained a cytochrome of the b
type which appeared, from difference spectra, to function either in the
presence or absence of cyanide. From these studies Yocum and Hackett
concluded that cytochrome oxidase does function in the respiration of
the aroid spadix. However, to account for the cyanide-insensitive
respiration, Yocum and Hackett favor the view that there is an alternate,
cyanide-resistant pathway of electron transfer to 0 2 which involves a
cytochrome of the b type. Further support for this view is found in the
work of Bendall and Hill (258), who observed that mitochondria from
spadix of Arum maculatum contain a cytochrome (cytochrome b 7 )
which does not react with CO and is oxidized by air in the presence of
103 M HCN.
Cytochrome c oxidase activity of mitochondria from Arum maculaturn (259) and skunk cabbage (Symplocarpus
foetidus)
(260)
spadices is inhibited strongly by cyanide (10
-3 M-10"
4 M). The succinoxidase activity of the same particles is also inhibited, but only to the
extent of 50-60%. These results indicate that succinate oxidation can be
effected by electron transfer in part through cytochrome c to 0 2 , and
this is the amount inhibited by cyanide. However, a cyanide-insensitive
route must also exist in these particles, the nature of which remains unknown. Similar conclusions result from studies on the oxidation of
DPNH by skunk cabbage spadix mitochondria (260). Since the autoxidizable, cyanide-insensitive cytochrome b is' present in these particles,
it is believed to be a component. The question of whether the cyanideresistant pathway can support oxidative phosphorylation has been
raised (257), but no information is available on this subject.
Microsomes of both plant (261) and animal tissues (262, 26S) contain cytochromes of the b type (cytochromes b 3 and b 5 respectively),
and these do not appear to be affected by cyanide. However, the
amount of oxidase activity in microsomes from the aroid spadix appears
insufficient to account for the amount of cyanide-insensitive respiration
which is present in that tissue. Since cytochrome b 3 is found in other
plant tissues (15), its role in respiration in plants needs to be examined
in more detail.
V. Conclusion
As emphasized elsewhere (1), half of the energy-yielding steps encountered in the metabolism of aerobic organisms occur during the
transfer of electrons from the pyridine nucleotides or flavoproteins to
0 2 . At the many different levels of the phylogenetic scale which have