448
ERIC E. CONN
studies on the cytochrome respiratory chain. The Keilin and Hartree
preparation is an insoluble preparation which catalyzes the oxidation of
succinate by molecular 0 2 (succinoxidase activity) through the cytochrome system. It therefore contains all of the enzymes and factors necessary to function between succinate and 0 2 (cytochromes b, c, a, a 3
and additional factors). Although succinate oxidation proceeds in the
absence of cytochrome c, the reaction is stimulated by the addition of
cytochrome c also. The preparation will also catalyze the oxidation of
ferrocytochrome c by molecular 0 2 (cytochrome oxidase activity), as
well as the oxidation of succinate by various acceptors such as cytochromes, ferricyanide, and different dyes. Although the latter activity
is frequently referred to as succinic dehydrogenase (38), recent studies
on the nature of the enzymes catalyzing these reactions has required
further development of terminology. Singer et ah (39) use the term
"succinic dehydrogenase" to mean the protein which catalyzes the reversible oxido-reduction of succinate to fumarate. This enzyme, which
has been extensively purified and is an iron flavoprotein, reacts most
rapidly with phenazine dyes, less rapidly with ferricyanide, and only
slowly with indophenol dyes, methylene blue, or cytochrome c. Green
(40) and co-workers use the term "succinic dehydrogenase complex" to
refer to a particulate preparation which catalyzes the oxidation of succinate by cytochrome c. It must therefore contain the succinic dehydrogenase described by Singer plus additional factors capable of reacting with cytochrome c.
Our knowledge of the succinoxidase system, although extensive, is
certainly not complete. This fact was stressed by Wainio and Cooperstein (14) who emphasized that "as study of the succinoxidase system
has proceeded, more and more factors have been postulated/' These
authors suggest that, although such factors may exist, the existence of
these components may "also be explained in terms of structural alteration" of the particulate preparations which can catalyze succinate
oxidation.
(2) Oxidation of Reduced Pyridine Nucleotides. In 1950 Slater (41)
examined the ability of the Keilin and Hartree succinoxidase preparation to oxidize DPNH. The preparation catalyzes both the oxidation of
DPNH by 0 2 (DPNH-oxidase activity) and that of DPNH by cytochrome c (DPNH-cytochrome c reductase activity). In his studies
Slater made extensive use of inhibitors such as cyanide, carbon monoxide, and British anti-Lewisite (BAL or 2,3-dimercapto-l-propanol),
which react with carriers in the cytochrome chain. Cyanide, carbon
monoxide, azide, and fluoride are inhibitors which bind iron-porphyrins and can react readily with cytochrome oxidase. On the other
ERIC E. CONN
studies on the cytochrome respiratory chain. The Keilin and Hartree
preparation is an insoluble preparation which catalyzes the oxidation of
succinate by molecular 0 2 (succinoxidase activity) through the cytochrome system. It therefore contains all of the enzymes and factors necessary to function between succinate and 0 2 (cytochromes b, c, a, a 3
and additional factors). Although succinate oxidation proceeds in the
absence of cytochrome c, the reaction is stimulated by the addition of
cytochrome c also. The preparation will also catalyze the oxidation of
ferrocytochrome c by molecular 0 2 (cytochrome oxidase activity), as
well as the oxidation of succinate by various acceptors such as cytochromes, ferricyanide, and different dyes. Although the latter activity
is frequently referred to as succinic dehydrogenase (38), recent studies
on the nature of the enzymes catalyzing these reactions has required
further development of terminology. Singer et ah (39) use the term
"succinic dehydrogenase" to mean the protein which catalyzes the reversible oxido-reduction of succinate to fumarate. This enzyme, which
has been extensively purified and is an iron flavoprotein, reacts most
rapidly with phenazine dyes, less rapidly with ferricyanide, and only
slowly with indophenol dyes, methylene blue, or cytochrome c. Green
(40) and co-workers use the term "succinic dehydrogenase complex" to
refer to a particulate preparation which catalyzes the oxidation of succinate by cytochrome c. It must therefore contain the succinic dehydrogenase described by Singer plus additional factors capable of reacting with cytochrome c.
Our knowledge of the succinoxidase system, although extensive, is
certainly not complete. This fact was stressed by Wainio and Cooperstein (14) who emphasized that "as study of the succinoxidase system
has proceeded, more and more factors have been postulated/' These
authors suggest that, although such factors may exist, the existence of
these components may "also be explained in terms of structural alteration" of the particulate preparations which can catalyze succinate
oxidation.
(2) Oxidation of Reduced Pyridine Nucleotides. In 1950 Slater (41)
examined the ability of the Keilin and Hartree succinoxidase preparation to oxidize DPNH. The preparation catalyzes both the oxidation of
DPNH by 0 2 (DPNH-oxidase activity) and that of DPNH by cytochrome c (DPNH-cytochrome c reductase activity). In his studies
Slater made extensive use of inhibitors such as cyanide, carbon monoxide, and British anti-Lewisite (BAL or 2,3-dimercapto-l-propanol),
which react with carriers in the cytochrome chain. Cyanide, carbon
monoxide, azide, and fluoride are inhibitors which bind iron-porphyrins and can react readily with cytochrome oxidase. On the other