||African clawed frog Xenopus laevis
||Lee E, Salic A, Krüger R, Heinrich R, Kirschner MW. The roles of APC and Axin derived from experimental and theoretical analysis of the Wnt pathway. PLoS Biol. 2003 Oct1(1):E10 p.120 table 1, p.121 table 2 & p.122 right column bottom paragraphPubMed ID14551908
||Abstract: "[Investigators] have developed a mathematical model for the canonical Wnt pathway that describes the interactions among the core components: Wnt, Frizzled, Dishevelled, GSK3beta, APC, axin, beta-catenin, and TCF [T-cell factor]. Using a system of differential equations, the model incorporates the kinetics of protein-protein interactions, protein synthesis/degradation, and phosphorylation/dephosphorylation. [They] initially defined a reference state of kinetic, thermodynamic, and flux data from experiments using Xenopus extracts. Predictions based on the analysis of the reference state were used iteratively to develop a more refined model from which [they] analyzed the effects of prolonged and transient Wnt stimulation on beta-catenin and axin turnover. [They] predict several unusual features of the Wnt pathway, some of which [they] tested experimentally."
||P.122 right column bottom paragraph: "In establishing quantities for [investigators'] model in Table 1, [they] found that the axin concentration (20 pM) is much lower than the concentration of the other major components (β-catenin, 35 nM, APC [adenomatous polyposis coli], 100 nM, Dsh [Dishevelled], 100 nM, and GSK3β [glycogen synthase kinase 3β], 50 nM). This unusual finding suggests that the function of the Wnt signaling system may actually depend on a low axin concentration."