Fig. 4. PPO inhibits proteolysis in alfalfa extracts in an o-diphenol-dependent manner. Proteolysis, as amino acid release over time, was measured in leaf extracts from Control- (Control-Alf, , •) or PPO-Alfalfa (PPO-Alf, , ) in the absence (, ) or presence (•, ) of added caffeic acid (CA, 3 mM final concentration). Results are the average ± SEM of three experiments using independently prepared extracts.