STUDY ON THE BLEACHING OF MONOMERS AND SUBUNITS OF R-PHYCOERYTHRIN BY TRANSITION METALS(Cu2+, Cd2+)

Abstract

he bleaching of the monomers and the separated α and β subnits of Rphycoerythrin from Polysiphonia urceolata by Cu2+, Cd2+, has been investigated. Upon the addition of Cu2+ and Cd2+, the visible absorption bands of the monomers at 496 , 538 and 564 nm of Rphycoerythrin was bleached. The change in absorption induced by Cu2+ or Cd2+ was accompanied by a decreased fluorescence emission intensity. The bleaching capacity of Cu2+ is greater than that of Cd2+. When monomers and α subunit are bleached by Cu2+, there is no appearance of the characteristic absorption of chromophore complex at 648 nm. But this absorption appeares obviously in the case of β subunit. From above results, we conclude the mechanism is that the bleachng of monomers and α subunit is caused by the interaction of Cu2+ or Cd2+ with the residues of polypeptides, but β subunit is bleached by both of the interaction of Cu2+ or Cd2+ with residues of polypeptides and the coordination of Cu2+ or Cd2+ with chromophores. 