PHOTOSYNTHETIC CYTOCHROMES-C IN CYANOBACTERIA, ALGAE, AND PLANTS

The cytochromes that function in photosynthesis in cyanobacteria, alga e, and higher plants have, like the other photosynthetic catalysts, be en largely conserved in their structure and function during evolution. Cyanobacteria and algae contain cytochrome c(6), which is not found i n higher plants and which may enhance survival in their planktonic mod e of life. Cyanobacteria and algae contain another cytochrome, low-pot ential c(549), which is not found in higher plants. This cytochrome ha s a structural role in PSII and may contribute to anaerobic survival. There is a third unique cytochrome, cytochrome M, in the planktonic ph otosynthesizers, and its function is unknown. New evidence is appearin g to indicate evolution of cytochrome interaction mechanisms during th e evolution of photosynthesis. The ease of cytochrome gene manipulatio n in cyanobacteria and in Chlamydomonas reinhardtii now provides great advantages in understanding of photosynthesis. The solution of tertia ry and quaternary structures of cytochromes and cytochrome complexes w ill provide structural and functional detail at atomic resolution.