Abstract: This papre studies quenching of proteins fluorescence by sulphated Hypocrellin(HA-SO₃).The experimental results show that the quenching of protein fluorescence by sul-phated Hypocrellin follows the classical Stern-Volmer equation. The variations of other conditions such as temperatures,viscosities,pH,guanidine-HCl ionic strength were also investigated.The sulphated Hypocrellin is an amphibious molecule with hydrophobic and hydrophilic.The quenching of various proteins may be at different mechanism;The quench fluorescence of protein tryphanyl residues is relatively large rate constant(the K_q values rang from 1-2 × 10¹³mol/L·s^-1).All results also show that HA-SO₃ is a more efficientquencher than others.

Key words: fluorescence quenching, protein, hypocrellin