Biology and Molecular Biology of Polyphenol Oxidase

Polyphenol oxidases (EC. 1.10.3.2) are ubiquitous in the plant kingdom, but little is known of their subcellular localization or physiological significance. Recent work in our and several other laboratories have succeeded in cloning and characterizing the genes encoding polyphenol oxidase from a variety of species. Analysis of the clones indicates a high degree of homology among the PPOs from the investigated species. The data indicate that PPOs are synthesized as precursor proteins having a transit sequence for transport into the chloroplast and lack sequences for specific targeting into the thylakoid membrane. Cloning of the genes for PPO offers the possibility to determine the physiological role of PPO within the chloroplast and to begin to manipulate the levels of PPO within specific organs to improve the characteristics of the desired commodity.