454
ERIC E. CONN
during the oxidation of α-ketoglutarate, pyruvate (plus malate), and
glutamate. No phosphorylation occurred during the oxidation of suecinate or DPNH.
Two other laboratories have recently reported the fragmentation
of rat liver mitochondria by sonic oscillations (79, 80). These particles
appear to be more highly organized units than those described by
Lehninger or than PETP, since they catalyze the oxidation of Krebs
cycle substrates in addition to succinate and DPNH and support phosphorylation during oxidation of all of the substrates. P/O ratios of approximately 1.0 were observed during the oxidation of succinate, DPNH,
glutamate, ß-hydroxybutyrate, isocitrate, and proline. The submitochondrial fragments obtained by these different procedures would therefore appear to be units in which the cytochrome respiratory chain and
the phosphorylation mechanisms are relatively intact. They may represent subunits of the structure of the mitochondrion itself.
D. DISTRIBUTION OF THE CYTOCHROME CHAIN
1. Evidence Based on Sequential Reduction and Oxidation of Carriers
The information on the distribution of the cytochrome respiratory
chain in nature consists of several types of evidence. Perhaps the most
complete evidence for the functioning cytochrome chain consists of
those studies in which sequential reduction and oxidation of the several
carriers of the chain have been observed. Unfortunately such studies
have been conducted on only a few tissues. Thus, the respiratory sequence shown in Scheme V has been observed directly in mitochondria
from rat and guinea pig liver and in the Keilin and Hartree succinoxidase particles. Similar observations have been made in intact yeast cells
and in ascites tumor cells (13).
Lundegardh (81) examined the cytochromes in roots of wheat plants
by spectrophotometric techniques and concluded that the route for
electron transfer through the cytochromes is from b to c to a. These
conclusions were based on the type of study employed by Chance and
Williams in which the sequence of reduction is observed directly. Recently Lundegardh has examined bakers' yeast (82).
2. Evidence Based on Oxidation of Succinate or the Reduced Pyridine
Nucleotides
Much of the evidence for the distribution of the cytochrome respiratory chain consists of studies on the oxidation of succinate and DPNH
by cell-free tissue preparations. The oxidation of succinate and DPNH
by a tissue preparation obviously is only indirect evidence that the cyto-
ERIC E. CONN
during the oxidation of α-ketoglutarate, pyruvate (plus malate), and
glutamate. No phosphorylation occurred during the oxidation of suecinate or DPNH.
Two other laboratories have recently reported the fragmentation
of rat liver mitochondria by sonic oscillations (79, 80). These particles
appear to be more highly organized units than those described by
Lehninger or than PETP, since they catalyze the oxidation of Krebs
cycle substrates in addition to succinate and DPNH and support phosphorylation during oxidation of all of the substrates. P/O ratios of approximately 1.0 were observed during the oxidation of succinate, DPNH,
glutamate, ß-hydroxybutyrate, isocitrate, and proline. The submitochondrial fragments obtained by these different procedures would therefore appear to be units in which the cytochrome respiratory chain and
the phosphorylation mechanisms are relatively intact. They may represent subunits of the structure of the mitochondrion itself.
D. DISTRIBUTION OF THE CYTOCHROME CHAIN
1. Evidence Based on Sequential Reduction and Oxidation of Carriers
The information on the distribution of the cytochrome respiratory
chain in nature consists of several types of evidence. Perhaps the most
complete evidence for the functioning cytochrome chain consists of
those studies in which sequential reduction and oxidation of the several
carriers of the chain have been observed. Unfortunately such studies
have been conducted on only a few tissues. Thus, the respiratory sequence shown in Scheme V has been observed directly in mitochondria
from rat and guinea pig liver and in the Keilin and Hartree succinoxidase particles. Similar observations have been made in intact yeast cells
and in ascites tumor cells (13).
Lundegardh (81) examined the cytochromes in roots of wheat plants
by spectrophotometric techniques and concluded that the route for
electron transfer through the cytochromes is from b to c to a. These
conclusions were based on the type of study employed by Chance and
Williams in which the sequence of reduction is observed directly. Recently Lundegardh has examined bakers' yeast (82).
2. Evidence Based on Oxidation of Succinate or the Reduced Pyridine
Nucleotides
Much of the evidence for the distribution of the cytochrome respiratory chain consists of studies on the oxidation of succinate and DPNH
by cell-free tissue preparations. The oxidation of succinate and DPNH
by a tissue preparation obviously is only indirect evidence that the cyto-