Re: ATP synthase


"rmj" <glenna@xxxxxxx> wrote in message news:Jkvii.3222$Od7.2872@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
From Wikipedia:

"The ATP synthase of mitochondria and chloroplasts is an anabolic enzyme
that harnesses the energy of a transmembrane proton gradient as an energy
source for adding an inorganic phosphate group to a molecule of adenosine
diphosphate (ADP) to form a molecule of adenosine triphosphate (ATP).

"This enzyme works when a proton moves down the concentration gradient,
giving the enzyme a spinning motion. This unique spinning motion bonds ADP
and P together to create ATP.

ATP synthase can also function in reverse, that is, use energy released by
ATP hydrolysis to pump protons against their thermodynamic gradient."

Anyone know (or can speculate as to) how the spinning motion would bond the
phosphate to ADP?

The spinning is probably incidental to the actual formation of the bond.
The proton itself may not be incidental, because forming the bond does require
that a proton be supplied to one of the oxygen atoms in the phosphate - thus
causing it to separate as water or hydroxyl and be replaced by a different
oxygen from the ADP. If you know some organic chemistry, I believe it
is an SN2 reaction with inversion of configuration at the phosphate.

However, some kind of motion of molecules is not incidental. All enzymes
move and change their shape in the course of doing their thing. In part,
this is just a matter of having one shape to facilitate acquiring the
substrates (phosphate and ADP and proton in this case), another shape for
actually doing the reaction, and a third shape for fascilitating the release
of the product (ATP in this case). And then, after the product is released,
the enzyme reverts to its original shape to acquire more substrate.
(But it may also be a matter of storing energy (as a kind of springiness)
on the upstroke to be released on the downstroke. By tuning the
springiness, you make the process run faster and more smoothly.)

In most enzymes, this motion is simply a kind of reciprocating, with no
rotation. But there are many - those involved in muscle contraction
and in nucleic acid polymerization, for example - in which one of the
substrates is periodic. In these enzymes, when the enzyme returns to
its original shape, it has moved one step in space - to the next location
on the periodic substrate. A kind of linear motor.

In a small number of enzymes, the periodic thing is wrapped into a circle
so that the enzyme moves in a circle in doing its thing. As I understand
it, the ATPase enzyme is a trimer with a periodicity such that three
steps brings you full circle. And there is also something about it that
is a little bit like the situation in a four-cycle internal combustion
engine in which some of the motion is caused by your own motive power and
some of it is a matter of being pushed along by what is happening in
another 'cylinder'.

Full disclosure. I've read about this stuff but forget many of the details.
So take this as an example of 'speculate as to' rather than as an example
of 'know'.

.

Relevant Pages

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  • Re: ATP synthase
    ... "The ATP synthase of mitochondria and chloroplasts is an anabolic enzyme ... "This enzyme works when a proton moves down the concentration gradient, ... rotated by a proton gradient sensitive proteinrather than being driven ...
    (talk.origins)