DERIVATION OF THE FORMYL-GROUP OXYGEN OF CHLOROPHYLL-B FROM MOLECULAR-OXYGEN IN GREENING LEAVES OF A HIGHER-PLANT (ZEA-MAYS)

Using mass spectroscopy, we demonstrate as much as 93% enrichment of t he 7-formyl group oxygen of chlorophyll b when dark-grown, etiolated m aize leaves are greened under white light in the presence of O-18(2). This suggests that a mono-oxygenase is involved in the oxidation of it s methyl group precursor. The concomitant enrichment of about 75% of t he 13(1)-oxygen confirms the well-documented finding that this oxo gro up, in both chlorophyll a and b, also arises from O2. High O-18 enrich ment into the 7-formyl oxygen relative to the substrate O-18(2) Was ac hieved by optimization of the greening conditions in combination with a reductive extraction procedure. It indicates not only a single pathw ay for Chl b formyl group formation, but also unequivocally demonstrat es that molecular oxygen is the sole precursor of the 7-formyl oxygen.