title: Nigericin forms highly stable complexes with lithium and cesium.
abstract: Nigericin is a monocarboxylic polyether molecule described as a mobile K+ ionophore unable to transport Li+ and Cs+ across natural or artificial membranes. This paper shows that the ion carrier molecule forms complexes of equivalent energy demands with Li+, Cs+, Na+, Rb+, and K+. This is in accordance with the similar values of the complex stability constants obtained from nigericin with the five alkali metal cations assayed. On the other hand, nigericin-alkali metal cation binding isotherms show faster rates for Li+ and Cs+ than for Na+, K+, and Rb+, in conditions where the carboxylic proton does not dissociate. Furthermore, proton NMR spectra of nigericin-Li+ and nigericin-Cs+ complexes show wide broadenings, suggesting strong cation interaction with the ionophore; in contrast, the complexes with Na+, K+, and Rb+ show only clear-cut chemical shifts. These latter results support the view that nigericin forms highly stable complexes with Li+ and Cs+ and contribute to the explanation for the inability of this ionophore to transport the former cations in conditions where it catalyzes a fast transport of K+ greater than Rb+ greater than Na+.
authors.affiliation: Departamento de Ciencias de la Salud, Universidad Autónoma Metropolitana-Iztapalapa, México, D.F.
authors.forename: R
authors.initials: R
authors.lastname: Alva
authors.forename: J A
authors.initials: JA
authors.lastname: Lugo
authors.forename: E
authors.initials: E
authors.lastname: Arzt
authors.forename: J
authors.initials: J
authors.lastname: Cerbón
authors.forename: B E
authors.initials: BE
authors.lastname: Rivera
authors.forename: M
authors.initials: M
authors.lastname: Toro
authors.forename: S
authors.initials: S
authors.lastname: Estrada
mesh_terms: D001692:Biological Transport; D002586:Cesium / Q000378:metabolism*; D007700:Kinetics; D008094:Lithium / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009550:Nigericin / Q000737:chemistry / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
chemical_list: D002586:Cesium; D008094:Lithium; D012964:Sodium; D012413:Rubidium; D009550:Nigericin; D011188:Potassium