Ergosta-4,6,8(14),22-tetraen-3-one (ergone) from many medicinal plants has been demonstrated to possess a variety of pharmacological activities in vivo and in vitro, including cytotoxic, diuretic and immunosuppressive activity. The effect of different solvents on spectral characteristic of ergone was investigated. The interactions between ergone and human serum albumin (HSA) and bovine serum albumin (BSA) had been studied by using absorption and fluorescence spectroscopy. Absorption and fluorescence spectral studies showed that binding to the serum albumins leaded to a blue shift of ergone together with a notable intensity change. Furthermore, the number of binding sites (n) was identified by the absorption spectra. The binding constant (K_a) and the free energy changes (ΔG) were obtained by analysis of fluorescence data of the ergone in the absence and presence of HSA and BSA according to Benesi-Hildebrand equation. Compared to BSA, HSA associated with ergone in a stronger way. A new fluorescence quantitative determination of proteins has been developed by using ergone as a fluorescence probe. Good calibration curves of the proteins were obtained in the range of (0.38～16.67)×10^－7 mol•L^－1 for HSA with detection limits (3σ) of 1.01× 10^－10 mol•L^－1, and (0.42～15.25)×10^－7 mol•L^－1 for BSA with detection limits of 1.22×10^－10 mol•L^－1. Most metal ions had no notable effect on the determination of proteins except Fe^3＋ ions which could quench the fluorescence intensity of ergone. Determination of proteins in human serum by this method gived results which were very close to those obtained by Coomassie Brilliant Blue colorimetry.

Key words: ergosta-4,6,8(14),22-tetraen-3-one (ergone), serum albumin, absorption spectroscopy, fluorescence probe, quantitative assay