Chlorophyllase

Chlorophyllase is an enzyme that catalyzes the hydrolysis of the phytol ester side chain of chlorophyll, yielding chlorophyllide and free phytol. The principal reaction can be written as chlorophyll + H2O → chlorophyllide + phytol. It is commonly classified as a serine hydrolase/esterase and is assigned to EC 3.1.1.14.

Distribution and localization: Chlorophyllase activity has been detected in many photosynthetic organisms, including higher plants and green algae. In plants, the enzyme is often associated with chloroplasts and thylakoid membranes, and can accumulate in tissues where chlorophyll is abundant or during developmental stages that involve chlorophyll turnover.

Biological role: The dephytylation reaction is proposed to initiate chlorophyll breakdown during senescence, fruit ripening, or stress, by producing chlorophyllide that subsequently enters the PAO pathway to form non-phototoxic catabolites. However, the relative contribution of chlorophyllase to in vivo chlorophyll degradation remains a matter of debate, and some organisms may degrade chlorophyll via chlorophyllide-independent routes.

Regulation and significance: Chlorophyllase activity is influenced by pH, temperature, and metal ions, with species- and tissue-specific differences in activity. Expression and enzyme activity often increase during leaf senescence or dark-induced chlorosis, aligning with roles in controlled chlorophyll turnover rather than rapid catabolism under all conditions. Ongoing research continues to clarify its exact contribution to chlorophyll metabolism in vivo.