Equilibrium binding of amphotericin B and its methyl ester and borate complex to sterols.

Scatchard analysis of the binding of amphotericin B to sterols in egg phosphatidylcholine/sterol vesicles revealed that amphotericin B was bound to ergosterol by approximately one order of magnitude more tightly than to cholesterol. Amphotericin B methyl ester formed a tighter complex with each of the sterols investigated than did amphotericin B, but the difference in the apparent binding constants towards ergosterol and cholesterol was not as large as with amphotericin B. Amphotericin B borate formed weaker complexes with vesicle-bound sterols than amphotericin B and amphotericin B methyl ester.