The Occurrence of Phenylalanine Ammonia-Lyase and Cinnamic Acid p-Hydroxylase on the Endoplasmic Reticulum of Cell Suspension Cultures of Glycine max

Abstract

Abstract 1. The time course of activity of soluble and microsomal phenylalanine ammonia-lyase (PAL) was studied in dark grown cell cultures of soybean (Glycine max). A distinct activity increase of PAL in the soluble and microsomal fraction occurred prior to the stationary phase of the cell culture. Cinnamic acid p-hydroxylase and NADH : cytochrome c reductase, too, exhibited maximal activity in the log phase, 5 days after the transfer of soybean cells to fresh culture medium. 2. Upon subfractionation of the once washed microsomal fraction by sedimentation velocity centrifugation on a sucrose gradient, membranes of the endoplasmic reticulum could be separated from fractions containing mainly membranes from the Golgi apparatus or plasma membranes, respectively. PAL and cinnamic acid p-hydroxylase were found in fractions of endoplasmic reticulum whereas no activity of either enzymes could be detected in fractions containing Golgi apparatus or plasma membranes. 3. Repeated washing of microsomal fractions led to a residual membrane-bound PAL representing about 1% of the total PAL activity of the cells. This residual membrane-bound activity could be solubilized almost completely by Triton X-100 or digitonin at concentrations of 0.5 - 5%.