Evidence that kidney lysosomal proteinases degrade the collagen of glomerular basement membrane.

Three thiol-dependent tissue proteinases have been isolated from human kidney cortex by methods using detergent extraction, gel chromatography, affinity chromatography and separation by ion-exchange. The properties of each enzyme toward several chromogenic low molecular weight substrates, azocasein and collagen indicate that they are similar to cathepsins B, H and L. All three enzymes degrade glomerular basement membrane at acid pH. Cathepsin B and L were particularly active against glomerular basement membrane. It has been demonstrated that in liver these enzymes exist together in lysosomes. These properties indicate that the kidney thiol proteinases may be an important factor in the turnover of glomerular basement membrane.