Contribution from coenzyme related molecules to evolution of photoreceptors

Coenzyme related substances, particularly flavins and pterins, were available from primordial chemical processes. When excited by near UV and short wave visible light, these compounds sensitise transfer of redox equivalents in homogenous solution and across membrane. Such reactions result in accumulation of free energy. The evolutionary age of some flavoproteins is close to the age of the Earth's biosphere. In modern organisms coenzyme related substances perform photosensor function for enzymes, such as DNA photolyase and nitrate reductase, and are chromophores for a photoreceptor regulating metabolism and development. Relevance of flavins and pterins both to prebiotic and current photobiological phenomena indicates their possible role in primitive photoreception.