FLUORESCENCE EMISSION, ENERGY-TRANSFER AND STRUCTURE OF PHYCOBILISOMES FROM NOSTOC-FLAGELLIFORME BORN ET FLAH DURING DISSOCIATION

Changes in fluorescence emission spectra (293 and 77 K) of phycobiliso mes from Nostoc flagelliforme during dissociation in phosphate buffer of various molarity were studied. There were three bands in 77 K fluor escence emission spectra of partly dissociated phycobilisomes: F648, F 666 and F686, characteristic of C-phycocyanin (C-PC), allophycocyanin (APC) and allophycocyanin-B (APC-B), respectively. In severely dissoci ated phycobilisomes, the F666 band was very weak, which indicated that linkage between C-PC and APC was severely dissociated, most of the en ergy trapped by C-PC could not be transferred to APC, but some of it c ould be transferred directly to APC-B. The phycobiliproteins in these phycobilisomes constitute an energy transfer chain: PEC-->C-PC-->APC-- >APC-B. A new model of phycobilisome structure is suggested, in which some C-PC contact directly with APC and others contact with APC-B.