The Lens Capsule: SUGAR AND AMINO ACID COMPOSITION

Abstract

Abstract Anterior and posterior portions of the lens capsules of calf and cow eyes were obtained free of cellular material by a procedure which included ultrasonic treatment. Sugar analyses indicated that approximately 11% of the dry weight of the capsules was in the form of monosaccharide residues, which were identified as glucose, galactose, mannose, fucose, hexosamines, and sialic acids. Small amounts of hexuronic acids were also present. The hexosamines consisted of glucosamine and galactosamine, which were present in the ratios of 92:8 in the calf anterior capsule and 93:7 in the calf posterior capsule. The sialic acids consisted of both N-glycolyl- and N-acetylneuraminic acids in the ratio of 60:40 in the anterior calf capsule and 65:35 in the posterior calf capsule. Distinct differences with age were noted in the composition of the lens capsule. Cow capsules contained larger amounts of glucose and galactose, and smaller levels of mannose and hexosamine than those from calves. Decreases in the sialic acid content were observed in the older animals while the fucose remained constant with age. The posterior portions of the capsules of both age groups contained less glucose and galactose than the anterior parts, but more sialic acid and hexuronic acid. The peptide portion of the capsules was characterized by the occurrence of a large amount of glycine (approximately one-fourth of the amino acid residues), as well as of hydroxyproline (10% of the amino acid residues) and hydroxylysine (4% of the amino acid residues). In addition, all of the commonly occurring amino acids were present, including cystine, methionine and tryptophan. Amide analyses indicated that nearly half of the dicarboxylic amino acids were in the uncharged form; in the anterior calf capsule 45% of these amino acids were in the amide form. An accounting of the charged groups of the capsules indicated that each had a net positive charge; the anterior calf capsule had a positive charge of 25 per 1000 amino acid residues. Of particular note in the amino acid composition of the lens capsules was the occurrence of very high hydroxylysine to lysine and hydroxyproline to proline ratios, which increased still further with age. While the composition of these lens capsules place them in the collagen group of proteins, they appear most closely related to other extracellular membranes, such as the renal glomerular basement membrane.