A Technique for the Assay of Enzymes in Intact Plant Cells in the Presence of Dimethylsulfoxide

Abstract

In our studies on the biosynthesis of tryptophan in callus tissue of Nicotiana tabacum var. Wisconsin 38 (3,4), we have made use of a convenient technique for the assay of enzymes in intact cells of this tissue. The technique involves the use of dimethylsulfoxide (DMSO), an agent which appears to alter the permeability properties of many cell types without effecting the activity of a variety of enzymes (1). By altering the permeability of intact cells with DMSO in order to facilitate the entry of substrates and release of reaction products, we hoped to observe activity for the enzymes of the tryptophan pathway without initially encountering the technical problems of denaturation which often occur in plant tissues in the preparation of cell-free extracts. Because our most extensive studies have been done, both in whole cells and in partially-purified preparations, with the terminal enzyme, tryptophan synthetase, data for this enzyme are presented here in order to show some of the characteristics of the