10. ELECTRON TRANSPORT AND OXIDATIVE PHOSPHORYLATION
471
P
32 0 4
3_ . The exchange of H 2 0
18 with ATP and inorganic phosphate
which is catalyzed by liver mitochondria during phosphorylation has
also been examined {179, 189, 190).
H. OCCURRENCE OF OXIDATIVE PHOSPHORYLATION
The occurrence of oxidative phosphorylation associated with electron
transport through the cytochrome respiratory scheme is indeed widespread. However, the detailed studies on the mechanisms of oxidative
phosphorylation have been carried out with mitochondria or other particulates from only a few tissues. These are rat liver (69, 75, 146, 147)
and beef (78) cat, pig, or rat heart (191).
Krebs et al. with the use of P
32 0 4
3 ~ have measured phosphorylation
in respiring tissue suspensions from rat liver, sheep heart, and pigeon
breast muscle (154). Mitochondria prepared from other tissues of rat
have been examined (192, 193, 194), as have particles from sheep kidney (195), rabbit heart (196), pigeon skeletal muscle, and the liver of
the Syrian hamster (197). In addition, oxidative phosphorylation associated with the oxidation of Krebs cycle substrates has been observed in
such interesting organisms as snails (198), locusts (199), blowflies (200),
houseflies (201), mosquitoes (202), and the parasitic helminth Ascaris
lumbricoides (203). The finding with the helminth is especially interesting, since the cytochrome respiratory chain is believed not to function
in this organism.
Oxidative phosphorylation was first demonstrated in higher plants by
Millerd et al., who isolated and studied particles from etiolated mung
bean seedlings (204, 205). Although the properties of these particles
resembled those of animal mitochondria, the P/O ratios obtained during
oxidation of various Krebs cycle substrates never exceeded 1.0. Shortly
following these studies other workers observed oxidative phosphorylation
with particles from cauliflower buds (206) and avocado fruit (207) in
which the P/O ratio exceeded 1.0. Particles have now been isolated
from etiolated lupine cotyledons (208), sweet potato roots (209), cabbage head (210), etiolated pea stems (211), and pea leaves (212)
which are just as efficient in carrying out phosphorylation as are animal
mitochondria. Phosphorylation has also been demonstrated to occur with
particles from soy bean hypocotyls (213, 214) and castor bean endosperm (215).
Ohmura (216) has observed oxidative phosphorylation during the
oxidation of Krebs cycle substrates by a particulate fraction from green
leaves. Although he concluded that these particles were chloroplast fragments, there is other evidence (217) to indicate that green leaves contain other particles which might be responsible for Ohmura's observa-
471
P
32 0 4
3_ . The exchange of H 2 0
18 with ATP and inorganic phosphate
which is catalyzed by liver mitochondria during phosphorylation has
also been examined {179, 189, 190).
H. OCCURRENCE OF OXIDATIVE PHOSPHORYLATION
The occurrence of oxidative phosphorylation associated with electron
transport through the cytochrome respiratory scheme is indeed widespread. However, the detailed studies on the mechanisms of oxidative
phosphorylation have been carried out with mitochondria or other particulates from only a few tissues. These are rat liver (69, 75, 146, 147)
and beef (78) cat, pig, or rat heart (191).
Krebs et al. with the use of P
32 0 4
3 ~ have measured phosphorylation
in respiring tissue suspensions from rat liver, sheep heart, and pigeon
breast muscle (154). Mitochondria prepared from other tissues of rat
have been examined (192, 193, 194), as have particles from sheep kidney (195), rabbit heart (196), pigeon skeletal muscle, and the liver of
the Syrian hamster (197). In addition, oxidative phosphorylation associated with the oxidation of Krebs cycle substrates has been observed in
such interesting organisms as snails (198), locusts (199), blowflies (200),
houseflies (201), mosquitoes (202), and the parasitic helminth Ascaris
lumbricoides (203). The finding with the helminth is especially interesting, since the cytochrome respiratory chain is believed not to function
in this organism.
Oxidative phosphorylation was first demonstrated in higher plants by
Millerd et al., who isolated and studied particles from etiolated mung
bean seedlings (204, 205). Although the properties of these particles
resembled those of animal mitochondria, the P/O ratios obtained during
oxidation of various Krebs cycle substrates never exceeded 1.0. Shortly
following these studies other workers observed oxidative phosphorylation
with particles from cauliflower buds (206) and avocado fruit (207) in
which the P/O ratio exceeded 1.0. Particles have now been isolated
from etiolated lupine cotyledons (208), sweet potato roots (209), cabbage head (210), etiolated pea stems (211), and pea leaves (212)
which are just as efficient in carrying out phosphorylation as are animal
mitochondria. Phosphorylation has also been demonstrated to occur with
particles from soy bean hypocotyls (213, 214) and castor bean endosperm (215).
Ohmura (216) has observed oxidative phosphorylation during the
oxidation of Krebs cycle substrates by a particulate fraction from green
leaves. Although he concluded that these particles were chloroplast fragments, there is other evidence (217) to indicate that green leaves contain other particles which might be responsible for Ohmura's observa-