Biology Reference
In-Depth Information
Fig. 8.1
A mechanism for converting chemical energy to mechanical energy based on the
generalized Franck-Condon principle (GFCP) (Reproduced from Ji 1974b). The
spheres
symbol-
ize enzyme active sites and the spring symbolizes the conformational deformability of enzymes.
The
dumb-bell-shaped objects
are multisubunit enzymes embedded in the inner mitochondrial
membrane. The first E·S complex (
a
) undergoes thermal fluctuations leading to the contraction and
relaxation cycle of the “spring” (
a
,
b
). When thermal motions bring the substrate-binding sites
close together at the transition state,
b
, two electrons are thought to flow (or
tunnel
) from AH
2
to B,
leading to (1) generation of electrical charges and (2) the stabilization of the “cocked” or energized
spring via the electrostatic attraction between separated charges. The unstabilized cocked spring in
b
corresponds to the Franck-Condon state harboring
virtual conformons
, and the stabilized cocked
spring in
c
corresponds to the mechanically deformed and energized state of the enzyme harboring
real conformons
. The
c
to
d
transition exemplifies the conformon-driven work processes, which in
this case is charge separation across the mitochondrial inner membrane
Although the concept of conformons was originally invoked to account for the
mechanism of oxidative phosphorylation occurring in mitochondria (i.e., the cou-
pling between the free energy-releasing oxidation of substrates and the free energy-
consuming ATP synthesis from ADP and Pi; see below), the first experimental
evidence for it was obtained in molecular biology, in the form of ATP-induced
supercoiling of circular DNA double helix in bacteria observed under electron
microscope in the mid-1960s (Stryer 1995, p. 795). The idea that biological
properties of enzymes (and molecular machines, by extension) may depend on
the mechanical (i.e., conformational) energy stored in proteins was first proposed
by R. Lumry and others in the 1950s and 1960s (Lumry and Gregory 1986)
(reviewed in Ji 1974b, 2000).
As indicated above, conformons were first invoked to explain the molecular
mechanisms underlying free energy transfer from one protein (or chemical reac-
tion) to another in mitochondria during energy-coupled process known as oxidative
phosphorylation (or oxphos for short) (Ji 1974b). During oxphos, the enzyme
