4. ENERGY-RICH COMPOUNDS
151
phoguanidoacetate and phosphoguanidotaurine, as shown in Eqs. 65
and 66:
Guanidoacetate + ATP ;=± Phosphoguanidoacetate + ADP
(65)
Guanidotaurine + ATP ;=± Phosphoguanidotaurine + ADP
66)
It has been assumed that guanidoethylserylphosphate is phosphorylated at the expense of ATP by reactions similar to Eq. 65 and 66 but
the responsible enzyme has not yet been demonstrated. The mechanism
of formation of guanidoethylserylphosphate has not been investigated.
c. Function. The recognition (324-326) that phosphocreatine and
phosphoarginine play an important role in an energy-requiring reaction
was achieved in the late 1920's. As described more fully in Vol. II,
Chapter 5, these compounds regenerate the ATP needed for muscle
contraction, and are, in turn, resynthesized by ATP when sufficient
amounts of the latter substance accumulate; Reactions 63 and 64 are
completely reversible. Since Reactions 65 and 66 are also reversible,
and phosphoguanidoacetate and phosphoguanidotaurine are the only
phosphogens found in some animals, it is assumed that these compounds
can also be mobilized for muscle contraction in a manner fully analogous to phosphocreatine and phosphoarginine. As stated above, no
enzyme capable of phosphorylating guanidoethylserylphosphate has
yet been demonstrated. However, this compound is the only phosphagen
found in the muscle tissues of Lumbricus terrestris and the amount
present (105) is comparable to that of N-phosphate compounds in
vertebrate tissues. On the basis of these considerations, the not unreasonable assumption has been made (105, 327, 329) that this compound, too, functions in ATP regeneration.
It is obvious that the ATP formed by transphosphorylation from the
phosphagens can be utilized for synthetic reactions,* or for mechanical
work, ion transport, or nerve transmission (371). While the greatest
amounts of amidine phosphates are found in muscle, these compounds
may occur in other tissues as well. For example, considerable amounts
of phosphocreatine have been found in mammalian liver (341) and,
similarly, varying amounts of phosphoarginine have been reported
from different invertebrate tissues (333).
* It has been shown that, in the presence of a phosphatase, phosphocreatine
can directly phosphorylate glucose and glycerol without intervention of the adenylic
system (370a, 370b). Likewise, a bacterial system has been found which can
utilize, for the phosphorylation of hexoses, phosphoramide (370c):
O
I
(HO-P-NH 2 )
151
phoguanidoacetate and phosphoguanidotaurine, as shown in Eqs. 65
and 66:
Guanidoacetate + ATP ;=± Phosphoguanidoacetate + ADP
(65)
Guanidotaurine + ATP ;=± Phosphoguanidotaurine + ADP
66)
It has been assumed that guanidoethylserylphosphate is phosphorylated at the expense of ATP by reactions similar to Eq. 65 and 66 but
the responsible enzyme has not yet been demonstrated. The mechanism
of formation of guanidoethylserylphosphate has not been investigated.
c. Function. The recognition (324-326) that phosphocreatine and
phosphoarginine play an important role in an energy-requiring reaction
was achieved in the late 1920's. As described more fully in Vol. II,
Chapter 5, these compounds regenerate the ATP needed for muscle
contraction, and are, in turn, resynthesized by ATP when sufficient
amounts of the latter substance accumulate; Reactions 63 and 64 are
completely reversible. Since Reactions 65 and 66 are also reversible,
and phosphoguanidoacetate and phosphoguanidotaurine are the only
phosphogens found in some animals, it is assumed that these compounds
can also be mobilized for muscle contraction in a manner fully analogous to phosphocreatine and phosphoarginine. As stated above, no
enzyme capable of phosphorylating guanidoethylserylphosphate has
yet been demonstrated. However, this compound is the only phosphagen
found in the muscle tissues of Lumbricus terrestris and the amount
present (105) is comparable to that of N-phosphate compounds in
vertebrate tissues. On the basis of these considerations, the not unreasonable assumption has been made (105, 327, 329) that this compound, too, functions in ATP regeneration.
It is obvious that the ATP formed by transphosphorylation from the
phosphagens can be utilized for synthetic reactions,* or for mechanical
work, ion transport, or nerve transmission (371). While the greatest
amounts of amidine phosphates are found in muscle, these compounds
may occur in other tissues as well. For example, considerable amounts
of phosphocreatine have been found in mammalian liver (341) and,
similarly, varying amounts of phosphoarginine have been reported
from different invertebrate tissues (333).
* It has been shown that, in the presence of a phosphatase, phosphocreatine
can directly phosphorylate glucose and glycerol without intervention of the adenylic
system (370a, 370b). Likewise, a bacterial system has been found which can
utilize, for the phosphorylation of hexoses, phosphoramide (370c):
O
I
(HO-P-NH 2 )