10. ELECTRON TRANSPORT AND OXIDATIVE PHOSPHORYLATION
453
Hartree (15), for example, described the cytochrome pathway substantially as it is presented in Scheme IV above. In an appropriately
titled article in the same volume in which the review by Chance and
Williams (IS) appears, Wainio and Cooperstein (14) discuss some of
the controversial aspects of the cytochromes. Their scheme does not include cytochrome b specifically and does not differentiate between cytochromes a and a 3 . These differences result from the fact that nearly all
of the components of the chain are associated with the insoluble structures of the cell. For the purpose of the present paper these differences
should not prove too great a disadvantage but should serve to emphasize that further modification may be necessary when more information
is obtained. Although more information can be obtained in part by
solubilization and purification of the components of the carrier chain,
the value of direct observation of the respiratory chain in intact cells
or in unmodified cellular components such as mitochondria should not
be underestimated.
b. Submitochondrial Fragments. Lehninger and his associates have
been successful in fragmenting mitochondria into smaller units which
are capable of oxidative phosphorylation (49, 75, 76). The particles,
estimated to be 1/3000 the size of mitochondria, were prepared by
treating intact rat liver mitochondria with digitonin. The fragments
catalyze the aerobic oxidation of ß-hydroxybutyrate, DPNH, and succinate. They do not, however, oxidize any other member of the Krebs
cycle, and they do not oxidize fatty acids. Of major importance is the
ability of these particles to carry out oxidative phosphorylation. P/O
ratios approaching 3 were obtained with ß-hydroxybutyrate as substrate
(75).
The oxidation of DPNH by the digitonin particles is only partly inhibited by antimycin A, although this compound completely inhibits the
aerobic oxidation of ß-hydroxybutyrate. The authors conclude that
DPNH added to the digitonin fragments is oxidized by a non-phosphorylative DPNH-cytochrome c reductase (23) activity present in
their preparations. Spectral studies have shown that the digitonin particles contain a flavoprotein and cytochromes b, c, a, and a 3 . However,
no attempt was made to establish the sequence of the carriers as they
function in electron transfer.
Other workers have been successful in preparing submitochondrial
fragments which are capable of oxidative phosphorylation. In Green's
laboratory, alcohol fractionation of heart muscle sarcosomes has produced a phosphorylating electron transport particle (PETP) which
oxidizes ß-hydroxybutyrate, DPNH, succinate, and other Krebs cycle
intermediates (77, 78). P/O ratios in excess of 2 have been obtained
453
Hartree (15), for example, described the cytochrome pathway substantially as it is presented in Scheme IV above. In an appropriately
titled article in the same volume in which the review by Chance and
Williams (IS) appears, Wainio and Cooperstein (14) discuss some of
the controversial aspects of the cytochromes. Their scheme does not include cytochrome b specifically and does not differentiate between cytochromes a and a 3 . These differences result from the fact that nearly all
of the components of the chain are associated with the insoluble structures of the cell. For the purpose of the present paper these differences
should not prove too great a disadvantage but should serve to emphasize that further modification may be necessary when more information
is obtained. Although more information can be obtained in part by
solubilization and purification of the components of the carrier chain,
the value of direct observation of the respiratory chain in intact cells
or in unmodified cellular components such as mitochondria should not
be underestimated.
b. Submitochondrial Fragments. Lehninger and his associates have
been successful in fragmenting mitochondria into smaller units which
are capable of oxidative phosphorylation (49, 75, 76). The particles,
estimated to be 1/3000 the size of mitochondria, were prepared by
treating intact rat liver mitochondria with digitonin. The fragments
catalyze the aerobic oxidation of ß-hydroxybutyrate, DPNH, and succinate. They do not, however, oxidize any other member of the Krebs
cycle, and they do not oxidize fatty acids. Of major importance is the
ability of these particles to carry out oxidative phosphorylation. P/O
ratios approaching 3 were obtained with ß-hydroxybutyrate as substrate
(75).
The oxidation of DPNH by the digitonin particles is only partly inhibited by antimycin A, although this compound completely inhibits the
aerobic oxidation of ß-hydroxybutyrate. The authors conclude that
DPNH added to the digitonin fragments is oxidized by a non-phosphorylative DPNH-cytochrome c reductase (23) activity present in
their preparations. Spectral studies have shown that the digitonin particles contain a flavoprotein and cytochromes b, c, a, and a 3 . However,
no attempt was made to establish the sequence of the carriers as they
function in electron transfer.
Other workers have been successful in preparing submitochondrial
fragments which are capable of oxidative phosphorylation. In Green's
laboratory, alcohol fractionation of heart muscle sarcosomes has produced a phosphorylating electron transport particle (PETP) which
oxidizes ß-hydroxybutyrate, DPNH, succinate, and other Krebs cycle
intermediates (77, 78). P/O ratios in excess of 2 have been obtained