COPPER ENZYMES IN ISOLATED CHLOROPLASTS. POLYPHENOLOXIDASE IN BETA VULGARIS

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Abstract
A green leaf extract of spinach beet (chard) was fractionated by highspeed centrifugation into a suspension of chloroplast fragments and a "cytoplasmic fluid" practically free of chlorophyll. Polyphenoloxidase activity of the 2 fractions was tested by using catalytic amts. of catechol with ascorbic acid as substrate, and was found to be localized in the chloroplast suspension. The localization of polyphenoloxidase in the chloroplast suspension was confirmed by using several variants in manipulative technique: extraction of chloroplast fragments at a different pH, further disintegration of the chloroplast fragments, and the addition of a crude potato polyphenoloxidase to the leaf mash. Consistent with the copper-protein nature of the enzyme, its activity in the chloroplasts was inhibited by cyanide, Na diethyldithiocarbamate and CO. The inhibition by CO was not reversed by light.

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