Partial purification of latent Polyphenol oxidase from peach (Prunus persica L. Cv. Catherina).: Molecular properties and kinetic characterization of soluble and membrane-bound forms

This paper analyzes the kinetic and structural characteristics of polyphenol oxidase (PPO) from peach cv. Catherina. The PPO was obtained in a latent state in both the soluble and membrane-bound forms, and both forms were activated by acid shock and the detergent SIDS. Plant defense is the main function assigned to PPO, which would be activated by the acid environment resulting from tissue damage. On the other hand, it has been suggested that, physiologically, the role played by SIDS may be fulfilled by lipids. Native isoelectric focusing identified two acid isoforms of p/5.7 and 5.8 for the soluble form and one isoform with p/5.7 for the membrane-bound form. A partially denaturing SDS-PAGE revealed two very close bands of activity in both cases, but the Western blot performed on a totally denaturing SIDS-PAGE, using polyclonal antibodies against bean PPO, revealed a single band in the membrane-bound fraction with a molecular mass of 60 kDa.