assay did not detect significant binding. The spectra are presented in the same manner as in Fig. 1. Compounds tested are: (A) cAMP (5 mM), (B) GTP (130 mM), (C) O-phosphorylserine (5 mM), (D) O-phosphoryltyrosine (5 mM), (E) platelet activating factor (13.8 mM). Their chemical structures are shown in Table 1. A small number of cross peaks are affected in these spectra, but the perturbations are due to a small change in the pH (less than 0.1 pH unit). This conclusion is confirmed by the spectrum (F), in which the same set of peaks is affected by a small pH shift. Cross peaks that are particularly sensitive to pH changes are enclosed in blue boxes. Found at: doi:10.1371/journal.pone.0010479.s001 (0.83 MB TIF) Table S1 Summary of the NMR-based binding assays for potential RKIP ligands. References 1. Trakul N, Menard RE, Schade GR, Qian Z, Rosner MR (2005) Raf Kinase Inhibitory Protein Regulates Raf-1 but Not B-Raf Kinase Activation. J Biol Chem 280: 24931–24940. 2. 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