Absorption and fluorescence spectra of polyene antibiotics in the presence of 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 very high affinity (5.8 10(7) M(-1]) and a secondary binding site with an affinity one order lower than the primary sites. This secondary binding site was very sensitive to temperature change. Nystatin yielded only one type of binding sites with an affinity of 1.1 10(6) M(-1). An electrostatic component was found in the binding of both ligands, as well as an important disorder at the protein binding sites. However the secondary binding site for AMP showed negative entropic change value, which suggests different mechanism of binding respect to the primary one. Conformational change induced by the temperature in the albumin molecule was detected by nystatin binding. Fatty acids produced an interference in the binding of both antibiotics to albumin.