Pheophytinase

Pheophytinase (PPH) is a plastid-localized esterase that catalyzes the hydrolysis of the phytyl ester bond in pheophytin during the chlorophyll degradation pathway. The enzyme acts on pheophytin a and pheophytin b, producing pheophorbide and free phytol. This dephytylation step is an early, essential part of the chlorophyll breakdown sequence, preceding the action of pheophorbide a oxygenase (PAO), which opens the porphyrin ring.

PPH activity is associated with leaf senescence and stress-induced chlorophyll turnover. In higher plants, the enzyme is encoded by genes such as AtPPH in Arabidopsis thaliana, and loss-of-function mutants typically exhibit accumulation of pheophytin and a delayed progression of chlorophyll degradation, reflecting the enzyme’s role in efficient pigment catabolism.

Biochemically, pheophytinase is regarded as a serine hydrolase that acts specifically on the pheophytin substrate, consistent with the need to remove the phytol tail before subsequent catabolic steps. Its activity contributes to the color change observed in aging leaves and to the broader process of recycling chlorophyll components during plant senescence.

Overall, pheophytinase is a key enzyme in the plant chlorophyll catabolic pathway, linking the removal of the phytol group from pheophytin to the formation of pheophorbide and onward breakdown products.