Polyphenol Oxidase in the Respiration and the Salt Uptake of Storage Tissues3

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Abstract
The respiration and potassium uptake of beet and potato disks have been measured in the presence of protocatechuic acid. It is found that protocatechuic acid in a concentration of 10−3 to 3 × 10−3 M at pH 6, stimulates both oxygen uptake and carbon dioxide output. This stimulation of respiration is accompanied by a reduction in potassium uptake. Experiments with carbon monoxide indicate that polyphenol oxidase mediates the ‘extra’ respiration in the presence of protocatechuic acid, although this enzyme does not appear to play any part in the normal respiration, at least in 5 per cent oxygen. These results are considered in relation to previous claims concerning the role of polyphenol oxidase in salt uptake and respiration of potato disks. Potassium uptake by potato disks is light-reversibly inhibited by carbon monoxide, indicating the participation of cytochrome oxidase in salt uptake in this, as in other tissues.

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