Characterization of monophenolase activity of table beet polyphenol oxidase. Determination of kinetic parameters on the tyramine/dopamine pair

Polyphenol oxidase from table beet leaves was extracted in both soluble and membrane-bound forms. In both cases,the enzyme obtained was in its latent state. The latent form was activated by sodium dodecyl sulfate. The enzyme showed monophenolase and diphenolase activity. The monophenolase activity showed a lag period before the steady state rate (V-ss) was reached. This lag period depended on the pH, the enzyme and substrate concentrations, and the presence of catalytic amounts of o-diphenol. The experimental results correspond with the mechanism previously described for;PPO from other sources. The kinetic parameters for both soluble and membrane-bound forms on the tyramine/dopamine pair were determined.