In order to reveal the relationship between the structure and the function of flammulin and to make best use of this antitumor substance, the secondary structures of flammulin are studied by the circular dichroism spectroscopy. The far UV circular dichroism spectra of flammulin show a negative peak at 208 nm, with [θ]~2~0~8= - 6574deg·cm^2·dmol^-^1, and a negative shoulder at 223 nm. Based on computer analysis using CCA program, the secondary structure is assigned as α-helix 19.7%，β-pleated sheet and β-turn 50.1%, random coil and γ-turn 30.2%. About 77.4% of total CD spectra are contributed by the secondary structures, and 22.6% are contributed by disulphide bond and aromatic amino acid. The near UV circular dichroism spectra of flammulin give a broad negative peak at 268 nm. The secondary structures are relatively stable to pH and SDS. However the protein is sensitive to heat. The structure of flammulin remains well over a wide pH range (from 4.6 to 9.4). But more alkaline pH condition can denature flammulin irreversibly.

Key words: CIRCULAR DICHROISM, SOLUTION, STRUCTURE