-Several peroxidase isoenzymes (pI 8-9) from phase-partitioned Chinese cabbage plasma membrane oxidized l-tryptophan to indole-3-acetaldoxime as shown by (i) correlation of catalytic activity with benzidineguaiacol staining on isoelectric focussing (IEF) gels, (ii) inhibition of enzyme activity by polyclonal antisera directed against tobacco peroxidase isoenzymes (which cross-react with Chinese cabbage peroxidases) and (iii) inhibition of tetraguaiacol formation by l-tryptophan. Treatment of the outside-out plasma membrane vesicles with 1 M sodium chloride and sonification released only part of the membrane-bound tryptophan oxidizing enzyme activity, suggesting little non-specific binding of peroxidases to (or trapping in) the membrane vesicles.