A Third Glycopeptide (Nephritogenoside) Isolated from the Glomerular Basement Membrane

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Abstract
A new glycopeptide was isolated from the glomerular basement membrane (GBM) of normal rats. Unlike already known glycopeptides, this glycopeptide has biological activity (nephritogenic activity) to induce glomerulonephritis when injected once into the footpads of homologous animals. A close relationship was found between the nephritogenic activity and the non-dialyzable glucose content of this nephritogenic glycopeptide. Thus, the nephritogenic activity can be assessed quantitatively by estimating the content of “non-dialyzable glucose.” Chemical purification of the nephritogenic glycopeptide involved the selective removal of inactive glycopeptide containing galactose, mannose, and N-acetyl-glucosamine (but no glucose). Trichloroacetic acid (TCA) treatment was a simple but highly effective procedure for selective removal of this inactive glycopeptide. The non-reducing terminus of the nephritogenic glycopeptide is α-D-gluco-pyranoside, and the glycopeptide reacts specifically with concanavalin A, even in the crude state. We propose that the nephritogenic glycopeptide is not an artifact produced during exhaustive proteolytic digestion, but a natural substance having a fixed molecular shape, even in the crude state, and whose union with GBM-proper can be easily broken by proteolytic digestion.