The lipid intermediate pathway in the retina for the activation of carbohydrates involved in the glycosylation of rhodopsin.
The presence of and many of the properties of enzymes in the retina involved in the biosynthesis of key intermediates in the dolichol pathway of carbohydrate activation has been demonstrated. The formation of dolichol phosphate-mannose and of mannose-containing oligosaccharide-polyprenols, and their use as substrates in further biosynthetic reactions was shown. The biosynthesis of the core-region glucosamine-containing mono, di and tri-saccharide pyrophosphoryl polyprenols, and the novel function of GDP-mannose as a regulator in their biosynthesis, was described. The participation of the dolichol pathway in the glycosylation of rhodopsin was demonstrated by the inhibition of core-region glycosylation of this glycoprotein by the antibiotic, tunicamycin. Preliminary evidence was obtained that glycosylation of rhodopsin was not a requirement for its insertion into disc membranes.
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Lorand V. Johnson Laboratory for Research in Ophthalmology Department of Surgery, Division of Ophthalmology and the Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106 USA.