452
ERIC E. CONN
wavelength between oxidized and reduced biological samples. The degree of oxidation can be controlled by adding substrates, by depleting
the dissolved oxygen in the sample, and by maintaining anaerobic conditions. This method has the advantage of detecting small changes in
absorption of some components without interference by other strongly
absorbing substances.
With these techniques Chance and Williams have observed the
respiratory chain directly in intact mitochondria in which the process
of hydrogen and electron transfer is tightly coupled to the phosphorylation of ADP. This is in contrast to the non-phosphorylative oxidation of
DPNH and succinate catalyzed by the Keilin and Hartree muscle preparation. From spectral studies in which the mitochondria were exposed
alternately to an excess of DPNH or 0 2 , and to anaerobic conditions,
Chance and Williams concluded that cytochrome b functions in DPNH
oxidation (68). This conclusion, which is supported by observations
with intact yeast (70) and ascites tumor cells (71), is also in contrast
to results obtained with the Keilin-Hartree preparation.
Information on the sequence of carriers in the respiration chain has
also been obtained (68). One way in which this was done was by making 0 2 available to mitochondria in which the carriers were in the reduced state and observing the order in which the different carriers became reoxidized. Under these conditions the terminal oxidase (cytochrome a 3 ) was first reoxidized, then cytochrome a, the next carrier,
was oxidized and so on. The data obtained indicated that the chain has
the composition shown in Scheme V.
Substrate —* DPNH —> Flavoprotein —> Cytochrome b —> Cytochrome c
—> Cytochrome a —> Cytochrome a 3 —> 0 2 (V)
The position of succinic dehydrogenase in this scheme is less clear,
since purified succinic dehydrogenase does not contain cytochrome b
(72). However, Chance (13) suggests that the dehydrogenase may be
composed of flavoprotein and cytochrome b.
There is little doubt that a high degree of structural organization
must exist in any tissue preparation which exhibits succinoxidase or
DPNH-oxidase activity. At present, studies are being made of this organization as it exists in the mitochondrion. Components of the structure [succinic dehydrogenase (72, 73), succinic dehydrogenase complex (57), DPNH-cytochrome reductase (23, 24)] are being isolated
and examined. There are several recent evaluations of our present state
of knowledge (39, 55, 74).
It should be emphasized that there is not universal agreement regarding the composition of the respiratory chain shown in Scheme V.
ERIC E. CONN
wavelength between oxidized and reduced biological samples. The degree of oxidation can be controlled by adding substrates, by depleting
the dissolved oxygen in the sample, and by maintaining anaerobic conditions. This method has the advantage of detecting small changes in
absorption of some components without interference by other strongly
absorbing substances.
With these techniques Chance and Williams have observed the
respiratory chain directly in intact mitochondria in which the process
of hydrogen and electron transfer is tightly coupled to the phosphorylation of ADP. This is in contrast to the non-phosphorylative oxidation of
DPNH and succinate catalyzed by the Keilin and Hartree muscle preparation. From spectral studies in which the mitochondria were exposed
alternately to an excess of DPNH or 0 2 , and to anaerobic conditions,
Chance and Williams concluded that cytochrome b functions in DPNH
oxidation (68). This conclusion, which is supported by observations
with intact yeast (70) and ascites tumor cells (71), is also in contrast
to results obtained with the Keilin-Hartree preparation.
Information on the sequence of carriers in the respiration chain has
also been obtained (68). One way in which this was done was by making 0 2 available to mitochondria in which the carriers were in the reduced state and observing the order in which the different carriers became reoxidized. Under these conditions the terminal oxidase (cytochrome a 3 ) was first reoxidized, then cytochrome a, the next carrier,
was oxidized and so on. The data obtained indicated that the chain has
the composition shown in Scheme V.
Substrate —* DPNH —> Flavoprotein —> Cytochrome b —> Cytochrome c
—> Cytochrome a —> Cytochrome a 3 —> 0 2 (V)
The position of succinic dehydrogenase in this scheme is less clear,
since purified succinic dehydrogenase does not contain cytochrome b
(72). However, Chance (13) suggests that the dehydrogenase may be
composed of flavoprotein and cytochrome b.
There is little doubt that a high degree of structural organization
must exist in any tissue preparation which exhibits succinoxidase or
DPNH-oxidase activity. At present, studies are being made of this organization as it exists in the mitochondrion. Components of the structure [succinic dehydrogenase (72, 73), succinic dehydrogenase complex (57), DPNH-cytochrome reductase (23, 24)] are being isolated
and examined. There are several recent evaluations of our present state
of knowledge (39, 55, 74).
It should be emphasized that there is not universal agreement regarding the composition of the respiratory chain shown in Scheme V.