ISOLATION, CHARACTERIZATION AND RECONSTITUTION OF PHYCOBILIPROTEIN ROD‐CORE LINKER POLYPEPTIDE COMPLEXES FROM THE PHYCOBILISOME OF <i>Mastigocladus laminosus</i>*

Abstract

Abstract A rod‐core complex, (αβ) 6 PC . L RC 29.5 ,(αβ) 3 APC .L C 8.9 , composed of hexameric phycocyanin (PC) and trimeric allophycocyanin (APC) subcomplexes associated to the CpcG2 gene product, has been isolated from the phycobilisome of Mastigocladus laminosus . Exactly the same complex was obtained by reconstitution using the subcomplexes(αβ) 3 PC . L RC 29.5 and (aβ) 3 APC .L C 8.9 as educts. Spectroscopic analysis of the isolated PC‐L R and PC‐L RC complexes from M. laminosus shows that the L RC cause the largest red‐shift in the absorbance and fluorescence emission maxima of PC. These results indicate that L RC mediate PC‐APC interactions in vitro . Only the CpcG2 polypeptide was able to promote this specific interaction, as neither CpcG3‐PC nor, as a negative control, CpcC‐PC complexes showed any reconstitution products with the core subcomplex (αβ) 3 APC .L c 8.9 . This is an indication that each of the four L RC in the phycobilisomes of M. laminosus and Anabaena sp. PCC 7120 attaches two peripheral rods specifically to one of four different core binding sites.