A terminal energy acceptor of the phycobilisome: the 75,000-dalton polypeptide of Synechococcus 6301 phycobilisomes--a new biliprotein.

Abstract

A rapid procedure is described for the isolation of linker polypeptides of cyanobacterial phycobilisomes. The 75,000 dalton component of the core of Synechococcus 6301 phycobilisomes isolated by this procedure carried a bilin similar in spectroscopic properties to phycocyanobilin. Renatured 75,000-dalton polypeptide has an absorption maxima at 610 and 665 nm and a fluorescence emission maximum at 676 nm, similar to that of intact phycobilisomes. A complex of allophycocyanin and a 40,000-dalton bilin-carrying fragment of the 75,000-dalton polypeptide, obtained by limited tryptic digestion, is described. This complex, which lacks allophycocyanin B, shows a fluorescence emission maximum at 676 nm. The 75,000-dalton polypeptide may function as a terminal energy acceptor in the phycobilisome.