128
F. M. HUENNEKENS AND H. R. WHITELEY
ATPase) may serve as the phosphate acceptor. When the acceptor ha;
the general structure
Y
II
R—X—ZH
as in Eq. 34b, the resulting phosphorylated product is "energy-rich'
and the equilibrium constant for the reaction is near unity. The ac
ceptor in this reaction may be an acyl, phosphoryl, enol, or guanidy
group.
In the second type of reaction (Eq. 35), ATP donates its pyrophos
phoryl group to the acceptor. The only well-established representative
of this class of reactions is the interaction of ATP with ribose-5-phos
phate to yield 5-phosphoribosyl-l-pyrophosphate plus AMP (92b)
Since Eq. 35 is an equilibrium reaction, it follows that the aldehyde
phosphate bond in the product may be relatively "energy-rich."
Finally in Reaction 36, ATP is again cleaved in a manner similar tc
that in Eq. 35; except that the adenylic acid portion, rather than the
pyrophosphate, is transferred to the acceptor. In all reactions of thi!
type, the acceptor forms an "energy-rich" linkage with the phosphate
group of the entering adenylate and the equilibrium constant is nea]
unity. The acceptor may be the terminal phosphate of a mononucleo
tide, a fatty acid, an amino acid, or sulfuric acid [see Table II of Korn
berg (50) for a summary of these reactions].
There is an additional class of ATP-dependent reactions, which i«
more complex than the preceding types inasmuch as 3 reactants are
involved. Glutamine synthesis may be cited as an example [see Table \
of Kornberg (50) for analogous reactions]:
Glutamate + NH 3 + ATP ^± Glutamine + ADP + Pi
(37
No phosphorylated or adenylated derivative of either glutamic acid o]
NH 3 has ever been detected as an intermediate in the reaction, anc
the detailed mechanism is unknown.
ATP has been implicated as the primary energy source for a num
ber of physiological processes of which the following may be cited ai
representative examples: muscle contraction and motility of certair
cells, transport of ions, water, and metabolites across membranes, rena
function, and transmission of electric impulses in nerve tissue. It i <
becoming increasingly apparent that underlying each of these organ oi
cellular functions is a complex series of enzymatic reactions, one oi
more of which ultimately depends upon ATP as an energy source. Ai
the present time, specific ATP-dependent reactions are being correlatee:
with many physiological processes, but in most cases the exact nature
and role of the enzymatic process is not yet understood.
F. M. HUENNEKENS AND H. R. WHITELEY
ATPase) may serve as the phosphate acceptor. When the acceptor ha;
the general structure
Y
II
R—X—ZH
as in Eq. 34b, the resulting phosphorylated product is "energy-rich'
and the equilibrium constant for the reaction is near unity. The ac
ceptor in this reaction may be an acyl, phosphoryl, enol, or guanidy
group.
In the second type of reaction (Eq. 35), ATP donates its pyrophos
phoryl group to the acceptor. The only well-established representative
of this class of reactions is the interaction of ATP with ribose-5-phos
phate to yield 5-phosphoribosyl-l-pyrophosphate plus AMP (92b)
Since Eq. 35 is an equilibrium reaction, it follows that the aldehyde
phosphate bond in the product may be relatively "energy-rich."
Finally in Reaction 36, ATP is again cleaved in a manner similar tc
that in Eq. 35; except that the adenylic acid portion, rather than the
pyrophosphate, is transferred to the acceptor. In all reactions of thi!
type, the acceptor forms an "energy-rich" linkage with the phosphate
group of the entering adenylate and the equilibrium constant is nea]
unity. The acceptor may be the terminal phosphate of a mononucleo
tide, a fatty acid, an amino acid, or sulfuric acid [see Table II of Korn
berg (50) for a summary of these reactions].
There is an additional class of ATP-dependent reactions, which i«
more complex than the preceding types inasmuch as 3 reactants are
involved. Glutamine synthesis may be cited as an example [see Table \
of Kornberg (50) for analogous reactions]:
Glutamate + NH 3 + ATP ^± Glutamine + ADP + Pi
(37
No phosphorylated or adenylated derivative of either glutamic acid o]
NH 3 has ever been detected as an intermediate in the reaction, anc
the detailed mechanism is unknown.
ATP has been implicated as the primary energy source for a num
ber of physiological processes of which the following may be cited ai
representative examples: muscle contraction and motility of certair
cells, transport of ions, water, and metabolites across membranes, rena
function, and transmission of electric impulses in nerve tissue. It i <
becoming increasingly apparent that underlying each of these organ oi
cellular functions is a complex series of enzymatic reactions, one oi
more of which ultimately depends upon ATP as an energy source. Ai
the present time, specific ATP-dependent reactions are being correlatee:
with many physiological processes, but in most cases the exact nature
and role of the enzymatic process is not yet understood.