SMALL MOLECULES AS PROBES FOR THE SECRETORY PATHWAY

Abstract

Markers for the unsignalled vesicular flow, the "bulk flow", from the Endoplasmic Reticulum (ER) and the Golgi apparatus were generated according to the following concept: A substrate analog that is able to diffuse through biological membranes is added to living cells. This substrate can be converted into a derivative that is unable to permeate membranes by a corresponding enzyme that is uniquely located to the organelle from which vesicular bulk flow is to be measured. If the non diffusable derivative reaches the medium of the cell culture, it must have been transported in the luminal side of vesicles, thus serving as a bulk phase marker. By use of diffusable substrate analogues that are radioactively labeled the kinetics of secretion of such bulk phase markers can easily be quantitated. Two examples for this approach are described.