Vitamin A Deficiency and the Glycoproteins of Rat Corneal Epithelium

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Abstract
The effect of vitamin A deficiency on in vitro incorporation of labeled precursors into glycoproteins of rat corneal epithelium was investigated. Whole corneas from deficient and pair-fed normal rats were incubated with radioactive precursors of glycoproteins; glycoproteins from the separated epithelial tissue were extracted and digested to yield glycopeptides. The glycopeptides eluted between 0.35 and 0.42 N LiCl by a continuous gradient from a DEAE—Sephadex column were found to be significantly affected by vitamin A deficiency. These affected glycopeptides were further separated by polyacrylamide gel electrophoresis and their carbohydrate content was assayed by gas—liquid chromatography. The results showed no fucose content and a much higher molar ratio of sialic acid to hexosamine (1.5 to 1.9) than that (0.3) of a similar vitamin A-sensitive glycopeptide previously isolated from rat small intestinal mucosa (De Luca, L., Schumacher, M. & Wolf, G. [1970] J. Biol. Chem. 245, 4551). It can be concluded that cornea contains a vitamin A-sensitive glycoprotein from which the affected glycopeptide is derived.