450
ERIC E. CONN
In contrast to this work is the observation by Chance (51) that the
rate of reduction of cytochrome b is not adequate to permit it to function in the oxidation of succinate by the non-phosphorylating heart muscle preparation. However, there is evidence that cytochrome b is a member of the carrier sequence linking both DPNH and succinate oxidation
to cytochrome c in intact phosphoryhting mitochondria (52). Therefore
Chance and Williams (13) suggest that in the non-phosphorylative
Keilin-Hartree preparation Slater's factor is that part of the cytochrome
b complex which is sensitive to inhibitors such as BAL. Slater's factor
has recently been described (15) as a structural factor or a measure of
the ability of cytochromes b and c to interact. Other authorities in this
field believe that the roles played by cytochrome b and "factor(s)"
which may link a reaction between cytochrome b and cytochrome c
are not yet defined. Apparently these questions can be settled only
after additional work (14).
b. Electron Transport Particle. Green and his associates have carried
out studies on a submitochondrial unit which they have termed the electron transport particle (ETP) (53-55). Two types of ETP can be obtained from heart muscle mitochondria, either by homogenizing the
particles in 8.5% sucrose, pH 8.5, or by alcohol fractionation in the
presence of KC1. Certain assumptions regarding the physical structure
of ETP in the mitochondrion have been made. The particles catalyze
the oxidation of succinate and DPNH by molecular oxygen in reactions
which are inhibited by cyanide and antimycin A. These particles therefore have properties in common with the Keilin and Hartree preparation
but, in contrast, do not require added cytochrome c. The latter when
added to ETP usually has no effect.
The ETP is considered to be the parent particle of two other particulate preparations known as succinic dehydrogenase complex (SDC) and
DPNH oxidase. The ETP can be fractionated with desoxycholate into
two components, a red and a green particle (56). The former will oxidize succinate (or DPNH) with cytochrome c or ferricyanide as acceptor, and contains, as determined spectrophotometrically, cytochromes
b and Ci. It therefore appears similar to SDC, which can be obtained
directly by treatment of beef heart mitochondria with alcohol (57).
SDC catalyzes the oxidation of succinate by cytochrome c, ferricyanide
and dyes. The green particle contains cytochromes b, c, and a and
catalyzes the oxidation of DPNH by 0 2 if cytochrome c is present. The
green particle also catalyzes the oxidation of ferrocytochrome c.
Green's laboratory has also described a DPNH-oxidase which is derived from ETP and does not have the ability to oxidize succinate (58).
The DPNH-oxidase has also been fractionated into a green and a red
ERIC E. CONN
In contrast to this work is the observation by Chance (51) that the
rate of reduction of cytochrome b is not adequate to permit it to function in the oxidation of succinate by the non-phosphorylating heart muscle preparation. However, there is evidence that cytochrome b is a member of the carrier sequence linking both DPNH and succinate oxidation
to cytochrome c in intact phosphoryhting mitochondria (52). Therefore
Chance and Williams (13) suggest that in the non-phosphorylative
Keilin-Hartree preparation Slater's factor is that part of the cytochrome
b complex which is sensitive to inhibitors such as BAL. Slater's factor
has recently been described (15) as a structural factor or a measure of
the ability of cytochromes b and c to interact. Other authorities in this
field believe that the roles played by cytochrome b and "factor(s)"
which may link a reaction between cytochrome b and cytochrome c
are not yet defined. Apparently these questions can be settled only
after additional work (14).
b. Electron Transport Particle. Green and his associates have carried
out studies on a submitochondrial unit which they have termed the electron transport particle (ETP) (53-55). Two types of ETP can be obtained from heart muscle mitochondria, either by homogenizing the
particles in 8.5% sucrose, pH 8.5, or by alcohol fractionation in the
presence of KC1. Certain assumptions regarding the physical structure
of ETP in the mitochondrion have been made. The particles catalyze
the oxidation of succinate and DPNH by molecular oxygen in reactions
which are inhibited by cyanide and antimycin A. These particles therefore have properties in common with the Keilin and Hartree preparation
but, in contrast, do not require added cytochrome c. The latter when
added to ETP usually has no effect.
The ETP is considered to be the parent particle of two other particulate preparations known as succinic dehydrogenase complex (SDC) and
DPNH oxidase. The ETP can be fractionated with desoxycholate into
two components, a red and a green particle (56). The former will oxidize succinate (or DPNH) with cytochrome c or ferricyanide as acceptor, and contains, as determined spectrophotometrically, cytochromes
b and Ci. It therefore appears similar to SDC, which can be obtained
directly by treatment of beef heart mitochondria with alcohol (57).
SDC catalyzes the oxidation of succinate by cytochrome c, ferricyanide
and dyes. The green particle contains cytochromes b, c, and a and
catalyzes the oxidation of DPNH by 0 2 if cytochrome c is present. The
green particle also catalyzes the oxidation of ferrocytochrome c.
Green's laboratory has also described a DPNH-oxidase which is derived from ETP and does not have the ability to oxidize succinate (58).
The DPNH-oxidase has also been fractionated into a green and a red