The incorporation of l-fucose into glycoproteins in the Golgi apparatus of rat liver and in serum

Abstract

l-Fucose was used as a radioactive precursor to study the synthesis of glycoproteins in the Golgi complex isolated from rat liver using both biochemical and au toradiographic techniques. Protein-bound fucose appeared in the Golgi complex of rat liver initially in the perchloric acid-insoluble fraction (maximum specific activity at 10 min after fucose injection) of the isolated Golgi comples and then in the perchloric acid-soluble fraction (maximum at 15 min) before being released in the perchloric acid-soluble fraction of serum. The results of biochemical studies correlated well with electron microscope autradiographic studies on sections of rat liver and isolated Golgi fractions labelled with l-[ 3H]fucose. Within 2 min, fucose was incorporated into the Golgi complex with the maximum number of silver grains over the Golgi complex observed at approximately 10 min, while the maximum number over the plasma membrane and associated vesicles appeared at 30 min. In isolated Golgi membranes, autoradiographic studies showed most radioactivity localized in the cisternae (maximum at 2 min) of the Golgi complex and then in the tubules (maximum at 10 min) befor appearing in the secretory vesicles (maximum at 20 min).