Conversion of Tryptophan to Indoleacetamide and Further Conversion to Indoleacetic Acid by Plant Preparations

Abstract

Horse radish peroxldase and cabbage preparations with peroxldase activity catalyzed the oxldative decarboxylatlon of tryptophan to indoleacetamide. Pyridoxal-5[image]-phosphate and Mn++ were required cofactors in this conversion. The further conversion of inoleacetamide to indoieacetic acid was demonstrated in cabbage seedlings and cabbage seedling homogenates. If the homogenates were dialyzed, there was a complete loss of amldase activity. No indoleacetamide could be detected after feeding DL-tryptophan-3-C14 to cabbage seedlings. Cabbage seedling homogenates contained potent inhibitors of the decarboxylation reaction which were removed by dialysis. An explanation is advanced as to how these observations would explain the lack of indoleacetamide formation in vivo. Small amounts of free indoleacetic acid were formed from tryptophan during the decarboxylatlon even when purified horseradish peroxldase was the enzyme used. There was no reaction between free indoleacetamide and horseradish peroxidase in the presence of pyridoxal-5[image]-phosphate and Mn++.