Cellular localization of particulate-bound polyphenol oxidase in tea leaves

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Cellular localization of polyphenol oxidase in tea leaves was investigated using Polyclar AT as an adsorbent of polyphenols existing in large amounts in the leaves. Two polyphenol oxidase fractions from the particulate fraction were separated from each other by sucrose density gradient centrifugation and called the heavy and the light fraction. The centrifugal pattern in the gradient indicated that the position of polyphenol oxidase in the heavy fraction coincided with those of the markers of peroxisomes, catalase and malate dehydrogenase, but not with those of mitochondria and chloroplasts, cytochrome c oxidase and chlorophyll. The peak of activity in the heavy fraction shifted toward lower density concomitantly with the increase of Polyclar AT content in the homogenizing medium. The heavy fraction was broken and disappeared at low pH condition, but the light fraction remained unchanged. The light fraction seemed to be a fragment of the heavy fraction. About 30% of the polyphenol oxidase activity was retained in the 10,000 × g pellet involving peroxisomes, even after repeated washings with the suspending medium containing 1 M KCl.
日本植物生理学会の論文