Glycoproteins of the Lens in Relation to age and Cataract Formation

I. Glycoproteins of the Bovine Lens Fibers

¹ Department of Ophthalmology, College of Physicians and Surgeons, Columbia University, New York, N. Y.

Bovine lens fibers contain significant amounts of a characteristic glycoprotein. This complex between a carbohydrate and a polypeptide can be completely extracted by heating for 18 hours at 90° C. with 0.6N trichloroacetic acid (TCA). It can be partly extracted by digestion with 80 percent ethanol containing 5 per cent KOH for 72 hours at room temperature. The carbohydrate of this glycoprotein consists of three hexoses, predominantly galactose with only small amounts of glucose and mannose, glucosamine, fucose, and so far an unidentified derivative of neuraminic acid. The content of neuraminic acid in the glycoprotein fraction extracted by TCA is several times as high as in that extracted by alkaline ethanol. This suggests that protein or lipid linked carbohydrate with high neuraminic acid content is present in lens fibers in addition to the glycoprotein extracted by alkaline ethanol. The total glycoprotein fraction sediments with the albuminoid of the lens fibers. The microsomal fraction and the soluble proteins of the lens fibers are free of any significant amounts of glycoprotein. The albuminoid of the nucleus of the lens fibers contains significantly less carbohydrate than that of the cortical part. The hypothesis is set forth that the glycoprotein of the lens fibers plays the role of a cement or lubricant substance between lens fibers which has been previously demonstrated by histochemical methods.