Abstract
Maize root peroxidases (POD) may also have polyphenol oxidase (PPO) activity as shown by using 3-amino-9-ethylcarbazole or DOPA as hydrogen donor to detect isoenzymes after disc gel electrophoresis. Copper chelators inhibited POD activity, and since PODs are haemoproteins, it can be concluded that copper chelators are not entirely specific for Cu enzymes. This raises the question whether PPO are only Cu enzymes. In POD preparations contaminated by catalase, POD activity could be over-estimated; this could be due to the auto-oxidation of the hydrogen donor or to stimulation of PPO activity by oxygen, as demonstrated with DOPA, dopamine and gallic acid. No correlation was found between the chemical nature of the substrate and the type of peroxidatic or oxidatic oxidation.
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