Chemical composition and solubility of human glomerular and tubular basement membranes of adult and senescent men.

The effect of aging on the composition of human renal basement membranes was studied in persons aged 22-90 years. The relative proportion of cortex in kidney appears to decrease with aging. Twenty pairs of GBM and TBM preparations were isolated using the detergent method. Protein content of the basement membrane preparations amounts to about 66% and is independent of type of membrane or age. Amino acid and carbohydrate analyses of both GBM and TBM revealed that the extents of hydroxylation of proline at the C4 position and of lysine decrease with aging. In the case of lysine this occurred from the seventh of life onwards. The decreases are probably not caused by a change of the collagen content. The extent of glycosylation of hydroxylysine is similar for all basement membrane preparations. An adapted protein assay is presented for solutions containing SDS and dithiothreitol. In the presence of these two compounds, solubility of GBM and TBM from adult and aged persons is similar and amounts to about 55 and 85% after 10 and 60 min, respectively, of heating at 95 degrees C. In SDS-polyacrylamide gels, no differences were observed for the major peptide bands between the preparations, irrespective of basement membrane type or age.