Nigericin forms highly stable complexes with lithium and cesium.
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+.
Alva
R
R
Departamento de Ciencias de la Salud, Universidad Autónoma Metropolitana-Iztapalapa, México, D.F.
Lugo
J A
JA
Arzt
E
E
Cerbón
J
J
Rivera
B E
BE
Toro
M
M
Estrada
S
S
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
D002586:Cesium; D008094:Lithium; D012964:Sodium; D012413:Rubidium; D009550:Nigericin; D011188:Potassium