Morphological changes of the molecular sieve in bovine glomerular basement membrane by protease and lysosomal enzyme digestion

Isolated and lyophilized bovine glomerular basement membrane (GBM) was digested in vitro with proteases such as collagenase, pepsin, trypsin and Pronase, and lysosomal enzymes which are believed to be involved in the pathogenesis of glomerulonephritis. Digested GBM was immediately observed by electron microscopy after negative staining. As has been already reported, untreated GBM has a definite fine three-dimensional meshwork structure of a molecular sieve with numerous pores and strands. After protease and lysosomal enzyme digestion, the regular meshwork was loosened, split and destroyed, and the pores were enlarged. By enzymatic digestion, round particles measuring approximately 70 to 300 Å in diameter and thin filaments measuring approximately 15 to 200 Å in diameter were observed around the digested fragments of GBM. From the present observations and the previous studies, it is presumed that the enlargement of the pores and the destruction of the GBM cause proteinuria and hematuria, respectively, in glomerulonephritis.