The content of o-diphenols and catechol oxidase activity was followed in developing apples from fruit set to harvest time.Afterwards their level drops, apparently due to conversion to other compounds and cessation of synthesis. Catechol oxidase activity shows a peak after that occurring in content of o-diphenols. As the fruit ripens, activity drops sharply in the particulate fractions. In the ripe apple a slight amount of soluble enzyme appears. These findings were correlated with the rate of browning of apple slices and the location of enzymes and their substrate in the fruit.Browning of slices could be prevented by dipping them into solutions of 1 m~-2,3-naphthalenediol or 2.5 7; N-vinyl-2-pyrrolidone. Addition of 1 mM-sodium ascorbate to the dipping medium improved the efficiency of prevention of browning.Content of o-diphenols shows a peak early in development.
transketolase; 1 j,M U-'4C-fructose-6-P, specific radioactivity 0.4 mcj,'mmole; 20 ,ig of chlorophyll in a total volume of 0.33 ml.The assay was performed at 20 C in a controlled temperature bath equipped with incandescent lighting of 1200 ft-c. The reaction was stopped by adding 0.34 ml of boiling absolute ethyl alcohol, and the tubes were removed to an 80 C water bath for 3 min. The test tubes were then centrifuged at 10,000g for 10 min, and the glycolate present in the supernatant fraction was determined. The supernatant fluid was applied to a Dowex AG 1X8 acetate (100-200 mesh) column (6 X 50 cm), and glycolate was eluted according to the method of Zelitch (33). After application of the sample the column was washed with 15 ml of H20. Glycolate was eluted with 10 ml of 4 M acetic acid. Paper chromatography in a 1-butanol, propionic acid, water solvent (9.4:3:4 v, 'v) confirmed that the eluate contained only glycolate. In this procedure more than 99.9%O of the U-14C-fructose-6-P applied was retained in the column. The recovery of added glycolate-U-14C was better than 95%c A 3-ml aliquot of the acetic acid eluate was placed in 15 ml of a liquid scintillation mixture consisting of 100 g of naphthalene,
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