Studies on the Renal Glomerular Basement Membrane

Glomeruli were prepared from bovine renal cortex with the use of sieves of varying mesh, both for the disruption of the tissue and for the separation of the glomeruli from other tissue components. Basement membranes, obtained by the ultrasonic treatment of these glomeruli, were shown to be free of cellular contaminants. Compositional studies performed on the glomerular basement membrane indicated that this structure is a glycoprotein with a carbohydrate content of approximately 9%. The sugar components present were identified as glucose, galactose, mannose, hexosamines, sialic acids, and fucose. The hexosamines consisted of both glucosamine and galactosamine in a ratio of 8.7:1.3, while the sialic acids occurred as N-glycolylneuraminic acid and N-acetylneuraminic acid in the ratio of 5.9:4.1. Essentially all of the sialic acid could be released by the action of neuraminidase or by mild acid hydrolysis. The peptide portion of the basement membrane was characterized by the presence of large amounts of glycine (one-fifth of the amino acid residues), as well as by the occurrence of substantial amounts of hydroxyproline (6.5% of the membrane weight) and hydroxylysine (2.8%). In addition, all of the commonly occurring amino acids were present, including half-cystine (2.7%), methionine (1.6%), and tryptophan (0.93%). Amide analyses indicated that 41% of the dicarboxylic amino acids were in the amide form. An accounting of the charged amino acid and sugar residues indicated that per 1000 amino acid residues there was a net positive charge of 14. Of interest among the properties of this membrane was its complete solubility under conditions of mild alkaline treatment.