Derivation of the formyl‐group oxygen of chlorophyll b from molecular oxygen in greening leaves of a higher plant (Zea mays)

Abstract

Using mass spectroscopy, we demonstrate as much as 93% enrichment of the 7-formyl group oxygen of chlorophyll b when dark-grown, etiolated maize leaves are greened under white light in the presence of ¹⁸O₂. This suggests that a mono-oxygenase is involved in the oxidation of its methyl group precursor. The concomitant enrichment of about 75% of the 13¹-oxygen confirms the well-documented finding that this oxo group, in both chlorophyll a and b, also arises from O₂. High ¹⁸O enrichment into the 7-formyl oxygen relative to the substrate ¹⁸O₂ was achieved by optimization of the greening conditions in combination with a reductive extraction procedure. It indicates not only a single pathway for Chl b formyl group formation, but also unequivocally demonstrates that molecular oxygen is the sole precursor of the 7-formyl oxygen.