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Abstract
Incubation of the albuminoid of bovine lenses with 7.5M urea at R.T. yields a fraction insoluble in 7.5M urea which represents 7 to 10 per cent of the total albuminoid. This fraction, can be dissolved by extraction with chloroform methanol into a fraction soluble in this solvent and an insoluble residue. Both these fractions do not differ essentially in the composition and in the ratio of this carbohydrate to protein. They are characterized, furthermore by a very low ratio of sialic acid and galactose which differentiates them clearly from gangliosides as found in brain red cells and in kidney. The carbohydrate content and proportion of carbohydrate to protein is higher in the equatorial region than in the polar and nuclear regions. In the equatorial region, in addition, one part of the urea-insoluble fraction sedimenting in the centrifuge at lower speed significantly differs in the composition of its carbohydrate from the fraction sedimenting only at higher speeds, insofar as the hexose component in the last fraction contains a much higher proportion of glucose which does not appear to be linked to hexosamine and is not extracted by chloroform methanol. The hypothesis is set forth that this glycoprotein and glycolipoprotein fraction insoluble in urea represents isolated fragments of the plasma membrane of the lens fibers.