112
Chapter 4
-0.32V
+0.82V
(-)
(NADH -*■ NAD+ +H+ +2e )
^11
----
r
Zero potential
(l/202 +2H+
+2e" —» H
2
O)
(+)
AEo = 0.82-(-0.32) = 1.14V
r
Figure 4.2 Galvanic element with the two single-electrode processes involved in the oxidation of
NADH.
The synthesized ATP is used almost immediately by free energy-requiring cell processes (e.g.,
polymerization processes), and the pool of ATP is in pseudo steady state on the time scale of the growth
process
NAD+
+ H 20 - N A D H - ± 0 2
= 0
;
AG°
= -220 k Jm o le 1
(1)
ATP + H 20
-
A D P - ~ P =
0
;
AG° - 30.5 kJ mole
1
(2)
The standard free energy associated with the oxidation of 1 mole of NADH is derived by consideration of
the two single-electrode processes that are combined to a galvanic element in Fig.4.2. The standard free
energy released by reduction of !402 by NADH is calculated from the electromotoric force AE0 of the
galvanic element:
-AG°
=nFAE0
=2-96.5-1.14 = 220 kJm ole
1
(3)
Synthesis of ATP is mediated by a membrane-bound ATPase (see Fig. 4.1). Its correct name is “FoFrtype
proton ATPase” or”ATP synthase”. Reaction between ADP and ~P on the knob-like FL
part of the protein,
which sticks into Ihe cytoplasm (for procaryotes) or into the mitochondria (for eucaryotes), proceeds readily
enough, but unless a steady stream of protons flows through the stem-like Fo part of the protein, which
transcends the membrane (cytoplasmic or inner mitochondrial), the synthesized ATP does not detach from
F
1
and ATP production stops. The flow of protons to F] is necessary to accomplish the release of ATP from
F,, and the overall effect of the proton flow is a considerable release of free energy, enough to drive the
chemical reaction in Eq. (2) against a negative affinity
Ap
(which is equal to -AG° ). The driving force -
also called the
protonmotive force A p
by Peter Mitchell (1961), who introduced the so-called
chemoosmotic hypothesis to explain the coupling between Eqs. (1) and (2)-is given by
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