The purification and characterisation of polyphenol oxidase from green bean (Phaseolus vulgaris L.)

Four isoforms of polyphenol oxidases (PPOs) were characterised in purified extracts of coats (PPOIa and PPOIb) and pods (PPOIIa and PPOIIb) of green bean (Phaseolus vulgaris L.). The molecular weights of four isoforms have been estimated to be from 57.5 to 39.0 kDa by SDS–PAGE. The PPOII (mixture of PPOIIa and PPOIIb) was used to characterise the PPO of green bean pods. All isoforms activities were stable between pH 6.8 and pH 7.2. PPOIa and PPOII have similar thermal inactivation profiles, and PPOIb has higher thermal stability than that of PPOIa and PPOII. PPOs showed the highest affinity to pyrogallol in all selected substrates. Although activities of PPOs were markedly inhibited by l-ascorbic acid, the activity of PPOI (mixture of PPOIa and PPOIb) was significantly activated by MnSO4 and CaCl2.