Abstract
Sequence alignments between membrane-spanning segments of pheophytin-quinone-type photosynthetic reaction centers, FeS-type photosynthetic reaction centers, core chlorophyll-proteins of PS II, chlorophyll t a/t b-containing antenna proteins of plants and light-harvesting complexes of purple bacteria led us to postulate a large common ancestral pigment-carrying protein with more than 10 membrane spans. Its original function as a UV-protector of the primordial cell is discussed. It is conceivable that a purely dissipative photochemistry started still in the context of the UV-protection. We suggest that mutations causing the t loss of certain porphyrin-type pigments led to the acquisition of redox cofactors and paved the way for a gradual transition from dissipative to productive photochemistry.
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