Studies on the Formation of Phycocyanin, Porphyrins, and a Blue Phycobilin by Wild-Type and Mutant Strains of Cyanidium caldarium

The synthesis of chlorophyll a and the bile-pigment and protein moieties of phycocyanin were arrested in illuminated cells of Cyanidium caldarium, strain III-D-2, incubated with chloramphenicol, ethionine, p-fluorophenylalanine, and p-chloromercuribenzoate. Pigment synthesis was similarly retarded in illuminated cells provided with nutrient medium lacking nitrogen.

Porphobilinogen, porphyrins, and a blue phycobilin were excreted into the nutrient medium by illuminated and unilluminated cells of wild-type and mutant C. caldarium strains incubated with δ-aminolevulinic acid in darkness. Pigment production from δ-aminolevulinic acid was sensitive to treatment with chloramphenicol and ethionine.

Cells of C. caldarium excreted 7 red-fluorescing porphyrins into the suspending medium during incubation with δ-aminolevulinic acid. Three of these porphyrins were identified as uroporphyrin III, coproporphyrin III, and protoporphyrin on the basis of their spectral properties and by paper chromatogaphy with standards.

The blue phycobilin was characterized spectrally and compared with biliverdin. The algal phycobilin displayed properties of a pigment with a violin-type structure. The phycobilin may be an immediate precursor of phycocyanobilin, the phycocyanin chromophore, or identical to it.