Accumulation of protoporphyrin IX and Zn protoporphyrin IX in Cyanidium caldarium.

In vivo fluorescence studies of Cyanidium caldarium mutants grown in the dark in dextrose-containing media have shown that these organisms accumulate protoporphyrin IX. In the dark the accumulated protoporphyrin IX is gradually turned into a metalloporphyrin, Zn protoporphyrin. In the light, in the chlorophyll-lacking mutant GGB, both compounds are degraded and phycobiliproteins are formed. These results implicate protoporphyrin IX in situ as the general precursor to tetrapyrrole pigments and Zn protoporphyrin IX as a possible intermediate or regulator in the biosynthesis of phycobilins.