Purification and N-terminal analyses of algal biliproteins

1. R-, B- and C-phycoerythrins and R- and C-phycocyanins were isolated and purified on a preparative scale by calcium phosphate chromatography, ammonium sulphate fractionation and crystallization. 2. The N-terminal residues of these biliproteins were analysed. Methionine is the only N-terminal residue of all the phycoerythrins, there being about 14 N-terminal residues per molecule of R- and B-phycoerythrins (mol.wt. 290000) and about 8 per molecule of C-phycoerythrin (mol.wt. 226000). Threonine (1 residue) is N-terminal in C-phycocyanin (mol.wt. 138000), and both threonine (about 1·3 residues) and methionine (5 residues) are N-terminal in R-phycocyanin (mol.wt. 273000). 3. Results suggest that the apoproteins of the various phycoerythrins are closely related, whereas C-phycocyanin has quite a different gross structure, and that R-phycocyanin contains two types of sub-unit, one related to C-phycocyanin and the other to the phycoerythrins.