Metabolic Dissipative Structures - Systems Biology of Metabolic and Signaling Networks - page 190

Fig. 8.3 Total information flows Bars represent the total information flow, defined per each
enzyme as the total outward TE minus the total inward. The functionality attributed for each
enzyme is an invariant and preserved along the route, i.e. E 2 is a source, E 3 is a sink, and E 1 has a
quasi-zero flow. A is the normalized amplitude of the periodic source of glucose substrate.
Adapted from Fig. 3 in (De la Fuente and Cortes 2012 )

TE input (Fig. 8.3 ). Positive values from that difference mean that that enzyme is a
source of causality flow, while negative numbers are interpreted as sinks or targets.
The maximum source of total transfer information (0.41) corresponds to the E 2
enzyme (phosphofructokinase) ¼ 0.021, when complex quasiperiodic

oscillations appear in the glycolytic system. For all conditions the enzyme E 2
(phosphofructokinase) is the main source of effective influence and the enzyme
E 3 (pyruvate kinase) a sink, which can be interpreted as a target from the point of
view of its effective functionality; the enzyme E 1 (hexokinase) appears as less
constrained with a flow close to zero. Accordingly, E 2 is the major source, E 3 is the
major sink, and E 1 is a minor source with a value close to zero.
The results of our model revealed in a quantitative manner that the enzyme E Z
(phosphofructokinase) is the major source of causal information and represents the
key core of glycolysis in this model. Biochemically, phosphofructokinase has been
considered a major checkpoint in the control of glycolysis (Gancedo and Serrano
1989 ; Heinisch et al. 1996 ). The main reason for this generalization is that phos-
phofructokinase exhibits a complex regulatory behavior that reflects its capacity to
integrate many different signals (Stryer 1995 ). From a dissipative point of view, this

for A