CU(II)-INDUCED CONFORMATION TRANSITION OF REGENERATED SILK FIBROIN IN AQUEOUS SOLUTIONS

Fluorescence quenching and far-UV circular dichroism(CD)were applied to reveal the mechanism for Cu(Ⅱ)to induce the conformation transition of silk fibroin.The results showed that Cu(Ⅱ)induced the conformation transition of silk fibroin by directly binding with certain amino acid residues in the hydrophobic regions.It indicats a different mechanism from that of ethanol-induced conformation transition process which is initiated by the destruction of hydrophobic interaction we proposed before.It was also found that the quenching of tryptophan(Trp)fluorescence by the quencher,Cu(Ⅱ),in regenerated silk fibroin solution was the combination of both dynamic quenching caused by collision and static quenching caused by the formation of ground-state complex.Thus we suggested that Trp was another probable binding site for silk fibroin to bind Cu(Ⅱ)besides His,and such a complexation was found to be reversible under certain conditions.