Multiple forms of soluble monophenol, dihydroxyphenylalamine: oxygen-oxidoreductase (EC 1.14.18.1) from potato tubers (Solanum tuberosum). II. Partial characterization of the enzyme forms with different molecular weights.

Gel chromatography on Sephadex G-200 was used to separate a soluble phenoloxidase from potatoes (var. Maritta) into at least six active fractions with dopa (dihydroxyphenylalanine) as substrate. Only high-molecular-weight-enzyme forms exhibited monophenoloxidase activity. Re-chromatography of the highest-molecular-weight form gave the same molecular weight distribution as with the crude enzyme. The molecular weights indicate association phenomena of subunits with a molecular weight of about 36000 daltons. According to polyacrylamide-gel electrophoresis, several monomeric forms with differnt isoelectric points seem to be present. This suggests that the large number of multiple forms of the enzyme arises from various combinations of identical and/or different subunits. SDS polyacrylamide gel electrophoresis failed to show the monomeric forms; the dimer and higher oligomers were obtained.