Multiple forms of soluble monophenol, dihydroxyphenylalanine: oxygen-oxidoreductase (EC 1.14.18.1) from potato tubers (Solanum tuberosum).

Upon polyacrylamide gel electrophoresis, a soluble phenoloxidase from potatoes (var. Maritta) revealed 17 multiple forms with activity towards dopa and almost all other o-diphenols tested, but only 5 of the forms reacted with monophenols. Isoelectric focusing of the crude enzyme resulted in 2 main peaks with activity towards dopa, having isoelectric points at pH ranges 4.0-4.7 and 5.1-5.4: smaller amounts of the enzyme at higher pI values were also detected. When activity peaks were controlled by polyacrylamide gel electrophoresis, all bands previously detected by electrophoresis of the crude enzyme were recovered, but all peaks were electrophoretically heterogeneous. Gel chromatography of the crude enzyme showed different molecular forms. Their molecular weights indicated monomer, dimer, tetramer, octamer and polymer (at least hexadecamer) forms with a monomer molecular weight of about 36000.