The Complete Amino-Acid Sequence of the α and β Subunits of B-Phycoerythrin from the Rhodophytan AlgaPorphyridium Cruentum

Abstract
Determination of the complete amino-acid sequence of the subunits of B-phycoerythrin from Porphyridium cruentum has shown that the .alpha. subunit contains 164 amino-acid residues and the .beta. subunit contains 177 residues. When the sequences of B- and C-phycoerythrins are aligned with those of other phycobiliproteins, it is obvious that B-phycoerythrin lacks a deletion at .beta.-21-22 present in C-phycoerythrin. However, relative to C-phycoerythrin from Fremyella diplosiphon (Calothrix) (Sidler, W., Kumpf, B., Rudiger, W. and Zuber, H. (1986) Biol. Chem. Hoppe-Syeler 367, 627-642), B-phycoerythrin has deletions at .beta.-141k-o, .beta.-142, .beta.-143, .beta.-147, .beta.-148. The four singly-linked phycoerythrobilins at positions .alpha.-84, .alpha.-143a, .beta.-84 and .beta.-155, and the doubly-linked phycoerythrobilin at position .beta.-50/61 are at sites homologous to the attachment sites in C-phycoerythrin. The aspartyl residues (.alpha.-87, .beta.-87, and .beta.-39), that interact with the bilins at .alpha.-84, .beta.-84, and .beta.-155 in C-phycocyanin, are found in the homologous positions in B-phycoerythrin. B-Phycoerythrin, in common with other phycobiliproteins, contains a N.gamma.-methylasparagine residue at position .beta.-72.

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