Figure 3
From: Finding the positive feedback loops underlying multi-stationarity
Examples.(A) For the ubiquitination system two positive feedback loops are found. The loops correspond to self-ubiquitination of Z and R, respectively. (B) There are two positive feedback loops. The right loop corresponds to the Michaelis-Menten mechanism involving the two species E and ES1. The left loop has four species nodes. The substrates S0 and S1 compete for the same kinase E in a way that enhances the production of both substrates: increasing S0, decreases the amount of E (reaction r 1) which decreases the rate of reaction r 7, which in turn increases the amount of S1. (C) Of the three positive feedback loops that are found, two correspond to the Michaelis-Menten mechanism (right side). One involves the kinase E and the complex ES0. The second is similar, involving the kinase S1 of the second layer and the complex S1P0. The left loop has five species nodes and illustrates P1-activation of the kinase E. (D) The apoptosis system has two loops. The left loop occurs because C 8∗ in reaction r 1 increases the amount of C 3∗, which in turn increases the amount of C 8∗ via reaction r 2.