In article <2i3mug$s03 at news.umbc.edu>
noronha at coe1.engr.umbc.edu (Santosh Noronha) writes:
>> (...) scheme deleted
>>As is apparent from the above scheme, each enzyme handles more than one
>reaction.
>> (...)
>> Also, would packages for MCA (metacon, gepasi etc ) be capable of handling
>such systems? ( I havent had a look at those yet, but would guess that they
>would calculate FCC based on elasticities rather than direct manipulation of
>flux data).
GEPASI does cope with a system like that. However, as it calculates the
control coefficients from the elasticities you would have to add some of these
to obtain the overall control coefficients of each enzyme (rather than each
step, which is what the program does). In your scheme, the flux control
coefficient of E1 is the sum of the flux control coefficients of steps 1 and 3.
Although GEPASI calculates the FCCs directly from the elasticities, you can
calculate them from modulations of enzyme concentration. For this you would
have to set up (at least) two simulations for each FCC (i.e. with two close
values of enzyme concentration), and then calculate the FCC by hand,
unsing:
logJ-logJ'
FCC = ----------
logE-logE'
where E and E' are the two values of the enzyme concentration, and J and J'
are the corresponding values of the flux. If you do this, you will verify
that the result is very close to the value obtained by the other method
(sum of the FCCs of all the steps catalysed by the enzyme). REMEMBER: the
two enzyme concentrations _must_ be close.
Also, consider the following paper:
Cascante, M., Canela, E.I. and Franco, R. (1990) Control analysis of systems
having two steps catalyzed by the same protein molecule in unbranched chains.
Eur.J.Biochem. 192, 369-371.
I hope this helps,
Pedro Mendes
prm at aber.ac.uk
