Cell Language Theory, The: Connecting Mind And Matter

The Bhopalator 135

“6x9” b2861 The Cell Language Theory: Connecting Mind and Matter

Fig

ure 3.36

The “Oster–Wang” mechanism of ion-driven rotation of the F

component of the F 0

F 0

–ATP synthase. The ion in this case is 1

Na

+ but the same mechanism is thought to hold for H

+. Reproduced from [163]. (Left) The subunit structure of the F

F 0

–ATP synthase. 1

(Right) (a) The structure of the rotor–stator assembly in

P. modestum

(an anaerobic bacterium). During ATP synthesis, the rotor turns to the

left as indicated by the arrow. The rotor section below the level of the membrane is thought to contain the 12 ion-binding sites, each consist

ing of the triad of Gln32, Glu65, and Ser66 which coordinates a sodium ion. The stator contains an aqueous channel that conducts ion from the periplasmic (

+) reservoir to the level of the horizontal hydrophilic strip below the membrane (see the dotted vertical arrow). The positive

charge, Arg227, on the stator blocks leakage of ions along the strip to the cytoplasm. (b) The postulated mechanism of sodium (or proton) gradient-driven rotation of the F

component of the ATP synthase, which causes the rotation of the 0

g-subunit transmitting its torsional energy

to F

which in turn causing the sequence of the conformational changes in the 1

a- and

b-subunits as required by ATP

synthesis from ADP

and P

as required by the mechanism in i

Fig

ure 3.35. A typical sequence of events that rotates the rotor by one step, i.e., 360°/12

= 30° is

depicted here. Initially the rotor is at step (1). The third site from the left is held by the stator charge, R227. In step (1)

→

(2), the stator

fluctuates due to Brownian motions so that the third site has the chance of escaping the electrostatic grip of the stator charge. This escaping is aided by (i) the trans-membrane potential (positive and acidic in the periplasmic space and negative and basic in the cytoplasm) pushing sodium ions into the ion channel and (ii) the dielectric barrier (see the dark gray vertical strip) that prevents the first rotor site (negatively charged) from entering the low dielectric medium of the stator. In step (2)

→

(3), once the third site enters the ion channel, it quickly binds

a sodium ion from the periplasmic reservoir. In step (3)

→

(4), the positive stator charge attracts the fourth empty (i.e., ligand-free) negative

site into its proximity and the neutralized second rotator site easily pass through the dielectric barrier and loses its sodium ion into the cyto

plasmic reservoir as indicated in step (4)

→

(5). Once empty, the site cannot return into the dielectric rotor–stator interface. State (5) is the

same as state (1), except that the rotor has rotated by one step, i.e., by 30°, coupled to the flow of one Na

+ ion (or a proton) through the F

(^0)
subunit. This Na
+-coupled rotation of the F
is thought to drive the rotation of the 0
g-subunit which is inserted into the center of the F
subunit 0
(see the left figure).
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