On the Nature of Isomeric Nonfluorescent Chlorophyll Catabolites in Leaves and Fruit - A Study with a Ubiquitous Phylloleucobilin and its Main Isomerization Product.

The typical main products of chlorophyll (Chl) breakdown in higher plants are non-fluorescent, colorless phyllobilins, named phylloleucobilins. These long elusive Chl-catabolites are linear tetrapyrroles, whose structure elucidation has required thorough spectroscopic analyses. Interestingly, in recent LC/MS studies of leaf extracts, isomeric forms of phylloleucobilins were detected. The existence of isomeric phyllobilins may suggest incomplete stereo-selectivity of catabolic processes, or isomerization processes in plant cells or in the analytes. Here we report a study with the phylloleucobilin NCC-1, a basic Chl-catabolite in extracts of leaves and fruit. NCC-1 and its main isomerization product in aqueous solution were identified as 82 -epimers. Formation of 82 -epi-NCC-1 from NCC-1 implies an unstable enol(ate)-intermediate, which reverts to NCC-1 or converts to 82 -epi-NCC-1. Such reversible epimerization reactions are a non-biological in vitro feature of typical phylloleucobilins, and probably also take place in vivo.