N-glycosylation of membrane glycoproteins in retinol-deficient rat liver.
The effect of vitamin A deficiency on N-linked oligosaccharides of membrane glycoproteins was studied in rat liver in order to evaluate the suggested role of retinol in protein N-glycosylation. First, oligosaccharides of newly synthesized glycoproteins from rough endoplasmic reticulum of vitamin A deficient liver were compared with that of pair-fed controls. Oligosaccharides were metabolically labelled with D-[2-3H]mannose, released from the glycoproteins with endoglycosidase H, purified by reversed phase HPLC and ion exchange chromatography, and were reduced with sodium borohydride. HPLC fractionation of the oligosaccharide alditols showed that the glycoproteins carried mainly four oligosaccharide species, Glc1Man9GlcNAc2, Man9GlcNAc2, Man8GlcNAc2 and Man7GlcNAc2, in identical relative amounts in the vitamin A deficient and the control tissue. In particular, no increase in the proportion of short chain oligosaccharides was noted in vitamin A deficient liver. Second, the number of N-linked oligosaccharides was estimated in dipeptidylpeptidase IV (DPP IV), a major glycoprotein constituent of the hepatic plasma membrane, comparing the newly synthesized glycoprotein from rough endoplasmic reticulum and the mature form of DPP IV from the plasma membrane. No evidence was obtained that retinol deficiency caused incomplete glycosylation of this membrane glycoprotein. From these data, the suggested role of retinol as a cofactor involved in the synthesis of N-linked oligosaccharides of glycoproteins must be questioned.
Institut für Klinische Chemie und Biochemie, Freie Universität Berlin, Germany.
R
R
Tauber
R
R
Nuck
W
W
Gerok
R
R
Büchsel
E
E
Köttgen
W
W
Lohle
C
C
Karasiewicz
W
W
Reutter
D000818:Animals; D002240:Carbohydrate Sequence; D018819:Dipeptidyl Peptidase 4; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D008099:Liver / Q000378:metabolism*; D008297:Male; D008362:Mannosides / Q000378:metabolism; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000737:chemistry; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000302:isolation & purification; D011134:Polysaccharides / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D014802:Vitamin A Deficiency / Q000378:metabolism*
D008362:Mannosides; D008562:Membrane Glycoproteins; D009844:Oligosaccharides; D011134:Polysaccharides; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D018819:Dipeptidyl Peptidase 4