PURIFICATION AND IDENTIFICATION OF APOPHYCOCYANIN ALPHA-SUBUNIT AND BETA-SUBUNIT FROM SOLUBLE-PROTEIN EXTRACTS OF THE RED ALGA CYANIDIUM-CALDARIUM - LIGHT EXPOSURE IS NOT A PREREQUISITE FOR BIOSYNTHESIS OF THEPROTEIN MOIETY OF THIS PHOTOSYNTHETIC ACCESSORY PIGMENT

Much controversy exists as to the level at which light exerts control over the biosynthesis of the photosynthetic apparatus in higher plants and other organisms. The eukaryotic red alga Cyanidium caldarium, lik e higher plants, undergoes light induction of chlorophyll synthesis. I n addition to chlorophyll a the alga also synthesises the linear tetra pyrrole phycocyanobilin, which is combined with alpha and beta apobili proteins to form phycocyanin, the major light-harvesting pigment in th is organism. We have previously shown that the tetrapyrrole precursor 5-aminolaevulinic acid (ALA) can substitute for light in inducing the biosynthesis of the phycocyanobilin moiety of this protein. We have al so described the appearance of a protein of similar isoelectric point and molecular weight to phycocyanin in ALA-fed cells (Turner et al., 1 992, Plant Physiol Biochem 30: 309-314). We now report on the protein' s immunological and sequence identity with phycocyanin alpha and beta subunits, and provide further evidence that bilin-apoprotein ligation is light dependent.