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Peroxidase (POD) and polyphenol oxidase (PPO) activities were monitored during the development of peach fruit (Prunus persica Batsch w. Redhaven) from shalk split stage to full maturation. Two extraction methods gave a discrepancy in activity for both enzymes. Two peaks of POD activities were observed and they corresponded to the two weight gain periods of the peaches. Polyphenol oxidase activity was very high at early development stage and declined to a constant level after the pit-hardened stage. Hydrophobic chromatography, using Phenyl-Sepharose CL-4B resin, provided a rapid partial purification and characterization of peach PPO. Several apparent forms of PPO and constant changes of these forms during development were observed. Upon cold storage of the acetone powder of peaches, an additional PPO isozyme much more tightly bound to the hydrophobic resin was noted. The technique could be very useful in studies of other food enzymes.

Three cDNA clones were isolated which code for the ubiquitous chloroplast enzyme, polyphenol oxidase (PPO), from Vicia faba. Analysis of the cloned DNA reveals that PPO is synthesized with an N-terminal extension of 92 amino acid residues, presumed to be a transit peptide. The mature protein is predicted to have a molecular mass of 58 kDa which is in close agreement to the molecular mass estimated for the in vivo protein upon SDS-PAGE. Differences in the DNA sequence of two full-length and one partial cDNA clones indicate that PPO is encoded by a gene family. Analysis of the deduced amino acid sequence shows that the chloroplast PPO shares homology with the 59 kDa PPOs in glandular trichomes of solanaceous species. A high degree of sequence conservation was found with the copper-binding domains of the 59 kDa tomato PPO as well as hemocyanins and tyrosinases from a wide diversity of taxa.

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