The monovalent cation site of pyruvate kinase and other enzymes: NMR investigations

Several monovalent cations have ideal physical properties for investigation of their interactions with biomacromolecules by NMR techniques. 7Li+, 14NH4+ and 133Cs+ have high natural abundance, and enriched samples of 6Li+ and 15NH4+ are easily obtained. All of these nuclei share the common property of having narrow line widths, thereby providing high sensitivity for NMR experiments. Numerous 23Na+ NMR studies have been reported but 39K+, 85Rb+, and 87Rb+ have not been studied extensively because these nuclei have low sensitivity and broad line widths. Recently NMR studies of monovalent cations have been extended to explore the monovalent cation sites of enzymes activated by such cations. With pyruvate kinase we determined that the extent of activation elicited by monovalent cations correlated well with the distance between the monovalent and divalent cations (structural site) sites. Those ions that were the best activators were closest to the M2+ site. In the course of this investigation we developed a general method to determine correlation times for dipolar relaxation between monovalent cation sites and paramagnetic centers on enzymes, and we have extended this work to other enzymes that are activated by monovalent cations