Studies on Mg-releasing Enzyme, Chlorophyllide-Mg-Dechelatase.

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The breakdown of chlorophyll (Chl) in crude extracts of Chenopodium album (white goose foot) in the dark was examined. Derivatives of pheophorbide a were formed when chlorophyll a or chlorophyllide a was incubated with depigmented crude extracts. The formation of pheophorbide was completely prevented by heat treatment of extracts, indicating that the reaction was enzymatic, and the presence of a Mg-releasing enzyme, the so called Mg-dechelatase, was postulated. This hypothesis was strongly supported by the observation that the formation of pheophorbide was inhibited by 51% by 10mM MgCl. Analysis by High-Performance Thin-Layer Chromatography (HPTLC) and liquid chromatography (HPLC) showed that the appearance of chlorophyllide a, pheophorbide'a, 13 -hydroxychlorophyllide a and pyropheophorbide a was accompanied by a concomitant decrease in levels of Chl a. It appears that Chl is degraded in a crude extract of C. album via the following enzymatically catalyzed reactions : Chl a ---- chlorophyllide a ---- pheophorbide a ---- pyropheophorbide a In the pathway of Chl breakdown, an accumulation of pheophorbide is not due to a lack of enzymes adn/or cofactors but may be explained by partial inhibition at the step distal to formation of pheophorbide derivatives which results in the accumulation of pheophorbide species. The purification and characterization of enzymes concerning the degradation of Chl are now in progress.