Figure 3.

Relative abundance of (a) InsP₆, (b) 5PP-InsP₅ and (c) InsP₈ in axial conformation at different pH and 50 µM total InsP concentration in the presence of 0/1/5 equivalents MgCl₂ and physiological background of 130 mM KCl and 10 mM NaCl. ¹H,¹³C-HMQC-NMR spectra were measured at 4 °C and integrated to obtain the ratio of eq. to ax. conformation. The proportion of ax. InsPs increases with pH, Mg²⁺ concentration and phosphorylation state (InsP₆ < 5PP-InsP₅ < InsP₈). Intriguingly, about half of InsP₈ molecules are in ax. conformation at physiological pH in the presence of five equivalents MgCl₂ (bar marked with *). To enable NMR detection, all samples were made up in D₂O. pH*-values measured in D₂O can be converted to pH using the following formula: pH = 0.929 × pH* + 0.42 [35]. Peaks of both conformations were integrated to obtain the relative abundance of axial vs. equatorial conformer.