Presence of lysosomal enzymes in the normal glomerular basement membrane matrix |
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Authors: | A K Singh |
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Institution: | (1) Department of Medicine, Section of Nephrology, Rush Medical College, Chicago, Illinois, USA;(2) Hines/Loyola Medical Center, Maywood, Illinois, USA;(3) Hines VA Hospital, Mail Slot 151, 60141 Hines, IL, USA |
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Abstract: | Summary The question posed in the present study was: are there hydrolytic enzymes, including proteases, present in the extracellular
matrix of the glomerular basement membrane? If these enzymes are present they may play a role in the catabolism of the glomerular
basement membrane (GBM) and removal of macromolecular debris resulting from ultrafiltration. Enzymes, acid phosphatase - the
marker for lysosomal enzymes - β-galactosidase, β-glucuronidase and acid protease (using albumin as substrate) were biochemically
assayed in purified basement membrane preparations. It was found that all enzymes were present in significant amounts in the
basement membrane. Compared to other enzymes, acid protease activity was present in much higher amounts. The pH optima of
these enzymes were variable but all had significant activity at neutral pH. A method was developed to localize the marker
enzyme, acid phosphatase, ultrastructurally in the basement membrane in order to substantiate the biochemical findings. Activity
was shown by the presence of dense deposits of lead phosphate. Staining for acid phosphatase could also be shown on isolated,
purified basement membrane. The demonstration of acid hydrolases in the GBM matrix argues for their role in (i) the extracellular
turnover of basement membrane macromolecules, and (ii) clearance of debris of ultrafiltration which tend to clog the membrane
pores. |
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