Spectroscopy features of the binding of polyene antibiotics to human serum albumin

The alteration in the fluorescence spectra observed for the polyene antibiotics nystatin and amphotericin B in the presence of human serum albumin is due to a decrease in the polar character of the antibiotic environment when these are bound to the protein. Amphotericin B showed two types of binding sites, the first having a very high affinity (5.8 x 10(7) M(-1)) and a secondary binding site with an affinity two orders lower than the primary site. This secondary binding site was very sensitive to temperature change. Nystatin yielded only one type of binding site with an affinity of 1.1 x 10(5) M(-1). Nystatin was found to be bound to fatty acid binding sites in albumin, while amphotericin B was not, suggesting that the fatty acid binding sites are not simple, depending on the number of unsaturated bonds on the polyene antibiotic molecule. Both polyene antibiotics displaced bilirubin bound to albumin, which is in agreement with the similarities of the affinity values of this chromophore and the polyene antibiotics with albumin.