A high molecular weight terminal pigment ("anchor polypeptide") and a minor blue polypeptide from phycobilisomes of the cyanobacterium Nostoc sp. (MAC): Isolation and characterization.

A 94 kD pigment-polypeptide, which is presumed to be involved in anchoring the phycobilisomes to the thylakoids, was isolated from Nostoc phycobilisomes by gel filtration in 63 mM formic acid. The isolation condition did not require detergents or denaturating reagents, as in previous procedures, and enzymatic degradation was not observed at the low pH of 2.5. The "anchor polypeptide" thus obtained had absorption (Abs) and fluorescence maxima (Em) at 658 and 673 nm, respectively, in 63 mM formic acid at room temperature. The maxima shifted to longer wavelengths in 100 mM potassium phosphate (pH 6.8), Abs 665 and Em 683 nm at room temperature, and Abs 665 and Em 684 nm at liquid nitrogen temperature. The fluorescence maxima at both temperatures correspond to the longest wavelength component resolved in phycobilisomes from second derivative spectra. A minor blue polypeptide was also found by this isolation method. The molecular weight of this polypeptide was ca. 18,000 and is probably similar to a polypeptide which has been found in the phycobilisome core of other cyanobacteria.