Hydroxymethylated phyllobilins: A puzzling new feature of the dioxobilin branch of chlorophyll breakdown

Abstract

Colorless nonfluorescent chlorophyll (Chl) catabolites (NCCs) are formyloxobilin-type phyllobilins, which are considered the typical products of Chl breakdown in senescent leaves. However, in degreened leaves of some plants, dioxobilin-type Chl catabolites (DCCs) predominate, which lack the formyl group of the NCCs, and which arise from Chl catabolites by oxidative removal of the formyl group by a P450 enzyme. Here a structural investigation of the DCCs in the methylesterase16 mutant of Arabidopsis thaliana is reported. Eight new DCCs were identified and characterized structurally. Strikingly, three of these DCCs carry stereospecifically added hydroxymethyl groups, and represent bilin-type linear tetrapyrroles with an unprecedented modification. Indeed, DCCs show a remarkable structural parallel, otherwise, to the bilins from heme breakdown. Turning pale: In senescent, yellow leaves of Arabidopsis thaliana (see photograph) colorless tetrapyrroles accumulate, which mostly belong to the dioxobilin-type chlorophyll catabolites (DCCs). In an Arabidopsis mutant several DCCs could be identified that carried an extra hydroxymethyl group, indicating an addition to the carbon skeleton during chlorophyll breakdown. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.