Since the email gateway at Daresbury seems to be ignoring contributions sent
by email, I am posting this on behalf of Stefan Schuster.
=======Forwarded by Stefan Schuster (address at the end)==========
I agree with David Fell's reply. In fact, one should use partial derivatives
when expressing the fluxes as functions of parameters only, and total
derivatives when expressing them as functions of parameters and
concentrations (which are, at steady state, in turn functions of the
parameters). So it is important in terms of what variables one expresses
fluxes and rates.
In order to reduce possible confusion, I suggest to use the term flux always
in sense that it is expressed in terms of parameters only, and to use the
term rate for the other situation (in accordance with the notion rate law,
which is a function of parameters and concentrations).
More difficult is an unambiguous terminology in the modular approach to
Metabolic Control Theory (which is a generalization of the top-down
approach). A crucial concept there are the fluxes going through some
module(s), which encompass several enzymatic reactions. They are functions of
the concentrations outside the module under consideration and certain
parameters. The concentrations inside the module can be "eliminated", because
they are functions of the parameters when the module has attained steady
state.
A possible term seems to be "bridging flux". Other suggestions are welcome.
Note that these "bridging fluxes" are steady-state fluxes when considered on
the level of the module, but rates on the level of the whole system.
Stefan Schuster (Berlin)
Stefan=Schuster at biologie.hu-berlin.de
