Isolation and Characterization of Golgi Membranes from Suspension-cultured Cells of Rice (Oryza sativa L.)

The isolation of Golgi membranes from suspension-cultured cells of rice (Oryza sativa L.) was attempted by linear glycerol density gradient centrifugation. When “burst” membranes in the pellet obtaind after differential centrifugation at 100,000 × g were suspended in 20% (w/w) glycerol in 50 mM malate-NaOH (pH 6.0) and loaded onto a linear density gradient of glycerol, which extended from 30 to 80% (w/w) in 1 mM EDTA in 50 mM glycylglycine-NaOH (pH 7.5), IDPase, a marker enzyme for Golgi membranes, was separated from other membrane markers on the glycerol gradient. In addition, UDPase and GDPase activities overlapped with the peak fraction of IDPase activity. Furthermore, membrane glycoproteins in each fraction were characterized by lectin-peroxidase staining. Concanavalin A and lentil lectin, which have the ability to bind to the high-mannose type of oligosaccharide, bound to glycoproteins distributed in ER membrane fractions, while wheat germ lectin, castor bean lectin, peanut lectin, and Ulex europaeus lectin-I which recognize the complex type and/or the mucin type of oligosaccharides interacted with glycoproteins in the Golgi membrane fractions but not with those in the ER membrane. These results strongly suggest that the oligosaccharide structures of glycoproteins in the ER membrane are of the high-mannose type, whereas glycoproteins in the Golgi membrane have modified N-linked and/or O-linked oligosaccharide chains.