Abstract
Purified mango cationic and anionic isoperoxidases catalyse the oxidation of guaiacol, o-dianisidine and 2,2′-azino-di-3-ethyl-benzothiazoline sulphonate (ABTS) at different rates. For an anionic isoperoxidase (A1) o-dianisidine is the most susceptible substrate, whereas for a cationic isoperoxidase (C1) ABTS is oxidised more rapidly. For indoleacetic acid (IAA), mixtures of anionic isoperoxidases catalysed the oxidation at higher rates than cationic isoperoxidases relative to their peroxidase activity towards o-dianisidine. For four purified isoenzymes the greatest rate of oxidation of IAA was found for A1. For dihydroxyfumarate (DHFA), mixtures of cationic isoperoxidases catalysed the oxidation at approximately twice that observed for anionic isoperoxidases per unit of peroxidase activity. Likewise, purified mango cationic isoperoxidases (C1 and C2) oxidised DHFA at a rate three times greater than that for the anionic isoperoxidases of identical peroxidase activity towards o-dianisidine. The mango anionic peroxidases have a greater molecular mass than the cationic isoenzymes. Molecular weights determined by gel filtration of 40 000, 44 000, 22 000 and 27 000 were found for mango isoperoxidases A1, A2, C1 and C2.
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