Trimming of glucoses from N-linked core glycans on newly synthesized glycoproteins occurs sequentially through the action of Glucosidases I and II in the endoplasmic reticulum (ER). Glucosidase II is an ER-localized enzyme that contains alpha and beta subunits (Glucosidase IIalpha and Glucosidase IIbeta). The alpha and beta subunits form a defined heterodimeric complex with a molecular weight about 161 kDa. Glucosidase IIalpha is the catalyitc core of the enzyme and can function independently of the beta subunit. The sequence of Glucosidase IIbeta encodes protein rich in glutamic and aspartic acid with a putative ER retention signal (HDEL) at the C terminus. The phosphorylated form of Glucosidase IIbeta is localized in the plasma membrane and is highly expressed in FGF stimulated fibroblasts and epidermal carcinoma cells. Glucosidase IIbeta was first purified from a human carcinoma cell line as a potential substrate for protein kinase C. Through the HDEL signal at the C-terminus, Glucosidase IIbeta retains the complete complex in the ER.