10. ELECTRON TRANSPORT AND OXIDATIVE PHOSPHORYLATION
455
chrome respiratory chain is functioning. By combining these experiments with studies of the action of inhibitors, more positive evidence for
the chain can be obtained. The tissue preparations studied range in degree of homogeneity and structural organization from crude homogenates to isolated mitochondrial and submitochondrial fractions. Mitochondrial preparations probably constitute the largest group of preparations which have been examined and, in most mitochondrial studies, the
aerobic oxidation of succinate will have been observed. The DPNHoxidase activity of mitochondria has been less frequently examined.
However, the DPNH-oxidase activity of rat liver mitochondria has been
extensively investigated with respect to the ability of this reaction to
support oxidative phosphorylation {88).
It would be impossible to list all the species or tissues from which
mitochondrial preparations have been obtained and studied. It would
be reasonably safe to assume that, with study and some care, mitochondria can be isolated from any higher plant or animal species and
that such preparations will contain succinoxidase or DPNH-oxidase activity.
In the past the heart, kidney, and liver of beef, horse, rat, and pig
have served as sources of cell-free preparations which exhibit succinoxidase or DPNH-oxidase activity {41, 45, 84-89). More recently rat
skeletal muscle (90) has been examined. DPNH-oxidase and succinoxidase activity has also been observed in the submitochondrial units represented by the Keilin-Hartree {41, 42) preparation, the electron transport particle {53), and DPNH-oxidase particle {58) obtained from
ETP.
DPNH-oxidase activity has been observed in homogenates of the
thoracic muscle of the house fly {91), the midgut of silk worm larvae
{92), and the flight muscles of the adult silk worm {92). The oxidation
of succinate has been examined in homogenates of flight muscle of blow
flies {93). Both DPNH-oxidase and succinoxidase have been detected
in homogenates of tetrahymena {94, 95). In the latter case the oxidations are atypical, however, since the reactions, although cyanide-sensitive, do not appear to involve cytochrome c.
The oxidation of succinate has been investigated in higher plants
{96-99) and has been observed to occur in a large number of plant
mitochondria (15, 100, 101). DPNH oxidation studies have been carried
out with mitochondria from potato tubers {102), from lupine cotyledons
{103), and with mitochondria and microsomes from the aroid spadix
{103a). In the studies on potato mitochondria, Hackett observed nearly
complete inhibition of DPNH-oxidase activity by antimycin A. In the
presence of added cytochrome c, antimycin A inhibited the rate of oxi-
455
chrome respiratory chain is functioning. By combining these experiments with studies of the action of inhibitors, more positive evidence for
the chain can be obtained. The tissue preparations studied range in degree of homogeneity and structural organization from crude homogenates to isolated mitochondrial and submitochondrial fractions. Mitochondrial preparations probably constitute the largest group of preparations which have been examined and, in most mitochondrial studies, the
aerobic oxidation of succinate will have been observed. The DPNHoxidase activity of mitochondria has been less frequently examined.
However, the DPNH-oxidase activity of rat liver mitochondria has been
extensively investigated with respect to the ability of this reaction to
support oxidative phosphorylation {88).
It would be impossible to list all the species or tissues from which
mitochondrial preparations have been obtained and studied. It would
be reasonably safe to assume that, with study and some care, mitochondria can be isolated from any higher plant or animal species and
that such preparations will contain succinoxidase or DPNH-oxidase activity.
In the past the heart, kidney, and liver of beef, horse, rat, and pig
have served as sources of cell-free preparations which exhibit succinoxidase or DPNH-oxidase activity {41, 45, 84-89). More recently rat
skeletal muscle (90) has been examined. DPNH-oxidase and succinoxidase activity has also been observed in the submitochondrial units represented by the Keilin-Hartree {41, 42) preparation, the electron transport particle {53), and DPNH-oxidase particle {58) obtained from
ETP.
DPNH-oxidase activity has been observed in homogenates of the
thoracic muscle of the house fly {91), the midgut of silk worm larvae
{92), and the flight muscles of the adult silk worm {92). The oxidation
of succinate has been examined in homogenates of flight muscle of blow
flies {93). Both DPNH-oxidase and succinoxidase have been detected
in homogenates of tetrahymena {94, 95). In the latter case the oxidations are atypical, however, since the reactions, although cyanide-sensitive, do not appear to involve cytochrome c.
The oxidation of succinate has been investigated in higher plants
{96-99) and has been observed to occur in a large number of plant
mitochondria (15, 100, 101). DPNH oxidation studies have been carried
out with mitochondria from potato tubers {102), from lupine cotyledons
{103), and with mitochondria and microsomes from the aroid spadix
{103a). In the studies on potato mitochondria, Hackett observed nearly
complete inhibition of DPNH-oxidase activity by antimycin A. In the
presence of added cytochrome c, antimycin A inhibited the rate of oxi-