Chlorophyll a degradation is the process in leaf senescence and fruit ripening observable due to its characteristic loss of green colouring. There are two pathways for chlorophyll a degradation. This second pathway, occurring in the chloroplast, is possibly the primary route by which chlorophyll a undergoes degradation in senescing leaves. First, the predicted enzyme pheophytin a synthase (coloured orange in the image) is theorized to dechelate Mg2+ in chlorophyll a to form pheophytin a. Second, pheophytinase catalyzes teh conversion of pheophytin into pheophorbide a and phytol. Third, pheophorbide a oxygenase, localized to the chloroplast membrane (coloured dark green in the image), catalyzes the conversion of pheophorbide into epoxypheophorbide a. Fourth, epoxypheophorbide and water spontaneously converts into red chlorophyll catabolite. Fifth, red chlorophyll catabolite reductase (RCCR) converts red chlorophyll catabolite into primary fluorescent chlorophyll catabolite.

Chlorophyll a Degradation II References