Evidence for a monooxygenase-catalyzed primary process in the catabolism of chlorophyll.

Only recently have products of the enzymatic breakdown of the chlorophylls been characterized for the first time. All catabolites isolated until now from a chlorophyte and from angiosperms have in common the position at which the primary oxygenative ring cleavage occurs, yielding linear tetrapyrroles (19-formyl-1[21H,22H]bilinones). In vivo studies of 18,18O2 incorporation in one of the chlorophyll catabolites isolated from Chlorella protothecoides show unequivocally that of the two oxygen atoms inserted into the pigment, only the formyl oxygen originates from dioxygen whereas the other one, the lactamic oxygen atom, derives from water. These findings suggest a monooxygenase-catalyzed primary process in the catabolism of chlorophyll.