The Association and Activities of Pteridines in Photosynthetic Systems*,†

Unconjugated pteridines are associated with the photosynthetic systems of several organisms. Inhibition of the development of the photosynthetic system of Rhodospirillum rubrum with the pteridine inhibitor 4‐phenoxy‐2,6‐diamino pyridine (PDAP) is reversed by biopterin, a natural pteridine. Evidence is presented which indicates an electron transport function for pteridines. Specific interaction of reduced pteridines with isolated pigment protein complexes, leading to red‐shifted absorption bands, has suggested a mechanism for photochemical energy trapping.