Partial Purification and Characterization of Latent Polyphenol Oxidase in Iceberg Lettuce (Lactuca sativa L.)

Polyphenol oxidase (EC 1.14.18.1), a thylakoid membrane-bound enzyme, was partially purified in iceberg lettuce ( Lactuca sativa L.) in its latent form using a two-phase partitioning approach with Triton X-114. The enzyme thus obtained was practically free of phenolic compounds and clorophylls and showed a recovery of 70%. Polyphenol oxidase was kinetically characterized with two phenolic substrates (4- tert -butylcathechol and chlorogenic acid) in both the latent and activated enzyme forms. The latent form was activated by sodium dodecyl sulfate (SDS) so that characterization was carried out in the presence and absence of SDS.