Biology Reference
In-Depth Information
Fig. 6. The (simplified) three modes of
P
∗
.
other, performing linear independent T-invariants, the parameters
gly
,
hex
and
rev
can, in principle, be
chosen arbitrarily. This implies that the relative frequency among this kind of conflicting reactions, for
example
l
2 and
m
1, depends merely on the choice of the parameters and not on a biochemical law that
would require a constant frequency ratio. In an organism, these reaction ratios are controlled mainly by
the current needs of the cell, governing the relative activities of the respective enzymes.
The flow of G6P or Gluc depends on the need for NADPH, R5P, and ATP in the cell. Based on
experimental observation, biochemists distinguish between four 'modes' (which we will call
T-modes
,
in order to not mistake them for the elementary flux modes) of the combined
GP
/
PPP
[see Stryer, 2006].
We finish this section with a short discussion of these T-modes and their relationships to our results,
neglecting again H
+
.
