Influence of K+ and Na+ ions on the aggregation processes of antibiotic amphotericin B: electronic absorption and FTIR spectroscopic studies.

The ionophore properties of amphotericin B (AmB) are related to the transport of Na(+) and K(+) ions across the molecular pores formed by this antibiotic in lipid membranes. In this paper, we present a new, complementary mechanism in which the -COO(-) group of the antibiotic is involved in the binding process of Na(+) and K(+) ions. Spectroscopic studies indicate that K(+) and Na(+) ions play an important role in the AmB aggregation process. Evidence in several spectral regions shows that K(+) ions exhibit a stronger ionic binding affinity to the -COO(-) group relative to Na(+). Overall, our findings indicate that monovalent ions can affect the molecular organization of AmB in substantially different ways not previously considered to be significant for their biological action.