Figure 5.

A sample network containing a hybrid metabolite. The cellular objective of the sample network (A) was to maximize Z and the system could be formulated as a linear programming problem (B). We attenuate the flux-sum of metabolite M1, which is also equal to x₁, and examine the effects on the objective Z. When x₁ was attenuated by decreasing the value of C, the maximum value of Z decreased as the objective function (red line) traversed the edges of the solution space (shaded region) in the direction shown by the blue arrow. As the objective function passes x₁ = 1, the "rate" of decrease of Z changes due to the difference in gradients of the edges.