4. ENERCY-mCH COMPOUNDS
147
Other enol phosphates have been considered as possible intermediates in enzymatic reactions: vinyl phosphate in photosynthesis (320b),
and phenol phosphates in oxidative phosphorylation (320c-320e).
d. Distribution. It is expected that PEP would be found in all plant,
animal, and microbial tissues capable of glycolysis (277). In addition,
specific enzymes (cf. Eqs. 54, 57, 59) capable of producing or utilizing
PEP have been reported from a wide variety of sources: spinach leaves
(293, 311), Crassulean plants (312, 313), wheat germ (295, 301), algae
(303), yeast (296, 321), photosynthetic (307), autotrophic (306, 308310), and heterotrophic (279, 302, 318-320) bacteria, and mammalian
tissues (273, 287, 288, 291-299, 314-317).
5. Thiol Phosphate: S-Phosphoryl Coenzyme A
Evidence has been presented (49) that S-phosphoryl coenzyme A
is formed as an intermediate in the activation of succinate by Escherichia colt. This compound has the general structure
O
CoA—S—P—OH
AH
The formula of the CoA molecule is detailed in Fig. 11,A. The over-all
reaction for the activation of succinate is shown in Eq. 60.
Succinate + ATP + CoA ^± Succinyl-CoA + ADP + Pi
(60)
This multicomponent reaction has been separated into two steps: (a)
an interaction of ATP and CoA mediated by the enzyme, Coenzyme A
thiokinase; and (b) a transfer reaction, catalyzed by the enzyme,
phosphoryl-CoA transferase. These reactions are indicated in Eqs. 61
and 62.
ATP + CoA ^± £-Phosphoryl-CoA + ADP
(61)
Ä-Phosphoryl-CoA + Succinate ;=± Succinyl-CoA + P»
(62)
The enzymes catalyzing Reactions 61 and 62 have been partially
purified with respect to each other, thus permitting the isolation (49,
49a) of S-phosphoryl-CoA via Reaction 61. Equilibrium studies of this
reaction indicate that the AF of hydrolysis of S-phosphoryl-CoA is approximately 2 kcal./mole more negative than that of ATP (49).
It has not been determined whether the postulated intermediate,
phosphoryl-CoA, is formed by other bacteria or by plant and animal
tissues. Data obtained in kinetic studies (169) with the succinate-activating enzyme of muscle and spinach were not compatible with the
formation of phosphoryl-CoA. However, preparations from brain have
147
Other enol phosphates have been considered as possible intermediates in enzymatic reactions: vinyl phosphate in photosynthesis (320b),
and phenol phosphates in oxidative phosphorylation (320c-320e).
d. Distribution. It is expected that PEP would be found in all plant,
animal, and microbial tissues capable of glycolysis (277). In addition,
specific enzymes (cf. Eqs. 54, 57, 59) capable of producing or utilizing
PEP have been reported from a wide variety of sources: spinach leaves
(293, 311), Crassulean plants (312, 313), wheat germ (295, 301), algae
(303), yeast (296, 321), photosynthetic (307), autotrophic (306, 308310), and heterotrophic (279, 302, 318-320) bacteria, and mammalian
tissues (273, 287, 288, 291-299, 314-317).
5. Thiol Phosphate: S-Phosphoryl Coenzyme A
Evidence has been presented (49) that S-phosphoryl coenzyme A
is formed as an intermediate in the activation of succinate by Escherichia colt. This compound has the general structure
O
CoA—S—P—OH
AH
The formula of the CoA molecule is detailed in Fig. 11,A. The over-all
reaction for the activation of succinate is shown in Eq. 60.
Succinate + ATP + CoA ^± Succinyl-CoA + ADP + Pi
(60)
This multicomponent reaction has been separated into two steps: (a)
an interaction of ATP and CoA mediated by the enzyme, Coenzyme A
thiokinase; and (b) a transfer reaction, catalyzed by the enzyme,
phosphoryl-CoA transferase. These reactions are indicated in Eqs. 61
and 62.
ATP + CoA ^± £-Phosphoryl-CoA + ADP
(61)
Ä-Phosphoryl-CoA + Succinate ;=± Succinyl-CoA + P»
(62)
The enzymes catalyzing Reactions 61 and 62 have been partially
purified with respect to each other, thus permitting the isolation (49,
49a) of S-phosphoryl-CoA via Reaction 61. Equilibrium studies of this
reaction indicate that the AF of hydrolysis of S-phosphoryl-CoA is approximately 2 kcal./mole more negative than that of ATP (49).
It has not been determined whether the postulated intermediate,
phosphoryl-CoA, is formed by other bacteria or by plant and animal
tissues. Data obtained in kinetic studies (169) with the succinate-activating enzyme of muscle and spinach were not compatible with the
formation of phosphoryl-CoA. However, preparations from brain have