Extraction and activity of polyphenoloxidase and peroxidase from senescing leaves of Protea neriifoiia

In a study to determine the causes of post-harvest browning of foliage of protea neriifolia R. Br. inflorescences, proteins were extracted using 7% (w/v) polyethylene glycol 4 000 as a tannin adsorbing agent in the extraction medium. Acetone precipitation of the proteins after extraction gave higher enzyme activities and better resolution during electrophoresis. The polyphenoloxidase activity doubled during the first 14 days after harvesting, while the peroxidase activity increased five-fold during the Same period. Only a slight increase in total soluble protein content could be detected. After 14 days the polyphenoloxidase electrophoretic pattern was completely different from that found immediately after harvesting. The peroxidase pattern did not change, although the intensity of the electrophoretic bands differed. Activation processes caused by a water deficit in the cells may have been responsible for part of the observed increase in enzyme activity. However, the post-harvest incorporation of 14C-L-alanine by six of the peroxidase isoenzymes indicates that at least some of the increase in activity may be due to de novo synthesis of the oxidizing enzymes. The increased activity of the oxidizing enzymes during the first 14 days after harvesting may have been responsible for the acceleration of post-harvest browning of P. neriifolia foliage