Re: modelling metabolism

[Tim Gwinn <***>]

> -----Original Message-----
> From: ROSEN Forum [mailto:*** Behalf Of Jannie
> Hofmeyr
> Sent: Monday, March 01, 2004 2:06 AM
> To: ***
> Subject: Re: modelling metabolism
>
--snip--
> In fact I learnt the most from just asking "what happens when we couple
two
> enzyme-catalysed processes together?" and then realising that I could use
> this to study what happens when, say, a biosynthetic supply pathway that
> leads to a product such an amino acid is coupled to a demand process such
> as protein synthesis that uses that product. Playing around with minimal
> models of such a system led Athel Cornish-Bowden and myself to realise
> that most of what one reads about the regulation of such pathways in
> textbooks is wrong and allowed us to come up with a much better
> explanation (http://www1.elsevier.com/febs/111/17/27/00023792.pdf) which
> has now also been corroborated experimentally.
>

Jannie,

Thanks for the article link. I don't pretend to understand it all, so maybe
the following question may make no sense. On p. 50, where you say:

"Supply-demand analysis shows that these two functions are inextricably
linked: the more control either block has over flux, the less it determines
the degree of homeostasis and the distance from equilibrium where
homeostasis is maintained, which becomes the function of the other block. A
common solution to this design problem in living cells is that the flux is
largely controlled by the demand block, whereas the supply block determines
homeostasis of the linking metabolite."

My question: this sounds fine if the system is limited to two blocks, one
acting as demand, the other as supply. But in a longer "chain" of such
blocks, it would seem that most of the blocks (those not on the ends of the
chain) would have to act as both demand and supply. In such a situation, how
would flux vs. homeostatic control be distributed, according to the
supply-demand model? What may be the same or similar question: can
homeostasis among the parts provide homeostasis for the whole?

Regards,
Tim