The oligosaccharide moiety of rhodopsin-its structure and cellular location.
The sugar chains of bovine rhodopsin released from opsin by hydrazinolysis were reduced with NaB((3)H)(4) and fractionated by paper chromatography. Three oligosaccharides were obtained. The structure of the major ((3)H)-oligosaccharide (ca. 60% of total) was elucidated by sequential exoglycosidase digestion, methylation analysis and endo-?-N-acetyl glucosaminidase D digestion. The structure of the sugar moiety of rhodopsin was thus identified as: Since the terminal GlcNac serves as galactose acceptor, the location of the sugar moiety of rhodopsin in the disc membrane was studied by incorporation of ((3)H)-galactose (from UDP-((3)H)-galactose) into the disk membrane. After inversion of disks by freeze-thawing, rhodopsin in the membrane incorporated one mole of ((3)H)-galactose per mole purified pigment. Intact disks incorporated lower amounts of ((3)H)-galactose. It was therefore concluded that the sugar moiety of rhodopsin is located on the internal surface of disk membrane. The results of lectin binding studies are consistent with the conclusion. Inverted disks, but not intact disks, bind concanavalin A (specific for ?-mannosyl residue) and wheat germ lectin (specific for N-acetylglucosamine). Since intact sealed rod outer segments bind concanavalin A, the sugar moiety of rhodopsin in the plasma membrane is probably exposed on the external surface of the rod.
Shichi
H
H
Laboratory of Vision Research, National Eye Institute, National Institutes of Health, Bethesda, MD 20205, U.S.A.
Adams
A J
AJ
Kobata
A
A