Partial Purification and Characterisation of Polyphenol Oxidase from Tomatoes (Solanum Lycopersicum)

Polyphenol oxidase (PPO) from tomatoes was extracted and partially purified through  (NH4)2SO4 precipitation, dialysis and ion exchange chromatography. The activity of polyphenol oxidase was investigated in solanum lycopersicum. Spectrophotometric method was used to assay the enzyme activity and the kinetic constants - maximum enzyme velocity (Vmax) and Michealis - Menten constant (Km). Of the substrates tested,  pyrogallol was the best substrate for PPO with a Km  value  of 1.5 mM. The optimum  pH for PPO activity  was  found to be 6.8. The enzyme showed high activity over a broad  pH range  of 4 - 8. The optimal  pH and  temperature for enzyme activity  were  found  to be  6.8 and 50-60 °C, respectively. km value for tomatoe PPO is calculated 25 mM for catechol and 1.5 mM for pyrogallol and 8.5 mM for L-dopa. As can be seen, affinity of PPOs for various  substrates varies widely. The enzyme showed a broad activity over a broad pH and  temperature range. The thermal inactivation studies showed that the enzyme  is heat resistant. The enzyme showed the highest  activity  toward  pyrogallol and no activity toward tyrosine. Of  the  inhibitors  tested,  the  most potent  inhibitors was  sodium  kojic acid