Physico-chemical and immunological properties of allophycocyanins.

Allophycocyanins were purified from diverse cyanobacteria and one rhodophytan alga (Cyanidium caldarium). The native proteins are trimeric molecules with the structure (alpha beta)3. Representative native allophycocyanins and their alpha and beta subunits were characterized with respect to molecular weight, amino acid composition, isoelectric point, absorption and fluorescence spectra and immunological properties. All of the allophycocyanins studied were strikingly similar with respect to each of these properties. Renatured alpha and beta subunits of allophycocyanin were distinct immunologically from each other, and both cross-reacted with the antiserum to the native protein. Trimeric allophycocyanin was readily reconstituted from the purified alpha and beta subunits. Formation of hybrid allophycocyanins was demonstrated by direct isolation and characterization of the hybrid proteins and by immunological techniques. The results support the view that allophycocyanins are a highly conserved group of proteins.