Cytochemical differentiation of the Golgi apparatus from GERL.

GERL exhibits a number of structural properties, such as its location at the trans face of the Golgi apparatus, thick limiting membranes with occasional coated regions, and close relationship to the ER, which are similar in all cells wehre it has been identified. Acid hydrolase activity and the formation of lysosomes, also considered characteristic of GERL, have been shown to be less consistent properties of GERL in some cells. Finally, GERL and the Golgi saccules of certain cells undergo significant changes in their cytochemical and structural properties in response to specific alterations in cellular activity. These variations are important for at least two reasons: first, they indicate the care required in differentiating GERL from the Golgi saccules based on limited cytochemical observations; second, and most important, they may yield information regarding the biogenetic and functional relationships between the ER, Golgi saccules, and GERL, such as the origin of GERL in various cells and the role of each organelle in the processing of lysosomal and secretory proteins.