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. Hierdie studie is onderneem ten einde ’n moontlike verwantskap tussen fenoliese verbruining en polifenoloksidase- en peroksidase-aktiwiteit in loofblare van Protea neriifolia R. Br. na oes vas te stel. Gedurende die eerste 14 dae na pluk is ’n vyfvoudige toename in die peroksidase-aktiwiteit waargeneem, terwyl die polifenoloksidase-aktiwiteit verdubbel het. Gedurende dieselfde tydperk het die polifenoloksidase-isosiempatroon heelwat verander. Die peroksidasepatroon het egter geen verandering ondergaan nie. Aangesien die totale oplosbare proteïenkonsentrasie slegs ‘n geringe toename toon, kan die toename in ensiemaktiwiteit nie sonder meer aan ‘n de novo sintese van die ensieme toegeskryf word nie. Dit is egter moont1ik dat sekere aktiveringsprosesse, wat as gevolg van watertekorte in die selle ontstaan, vir die toename in ensiemaktiwiteit verantwoordelik mag wees. Die inkorporering van 14C-L-alanien deur ses van die sewe peroksidase-isoënsieme toon egter dat ten minste ’n gedeelte van die toename in ensiemaktiwiteit aan de novo sintese van die oksiderende ensieme toegeskryf kan word. Dit blyk dus dat die toename in aktiwiteit van die oksiderende ensieme deur aktivering en/of sintese van die ensieme veroorsaak word. Die toename in aktiwiteit van die oksiderende ensieme is moontlik vir die vinniger naoesverbruining van P. neriifolia-loofblare verantwoordelik.