AN OLD ENZYME WITH A NEW FUNCTION - PURIFICATION AND CHARACTERIZATIONOF A DISTINCT MATRIX-DEGRADING METALLOPROTEINASE IN RAT-KIDNEY CORTEXAND ITS IDENTIFICATION AS MEPRIN

We have purified to homogeneity the enzyme in the kidney cortex which accounts for the vast majority of matrix-degrading activity at neutral pH. The purified enzyme has an apparent molecular mass of 350 kD by g el filtration and of 85 kD on SDS-PAGE under reducing conditions; and it degrades laminin, type IV collagen and fibronectin. The enzyme was inhibited by EDTA and 1,10-phenanthroline, but not by other proteinase inhibitors. The enzyme was not activated by organomercurials or by tr ypsin and was not inhibited by tissue inhibitors of metalloproteinases indicating that it is distinct from the other matrix-degrading metall oproteinases. Unexpectedly, the amino acid sequence of the NH2-termina l and two internal peptides of the enzyme showed complete homology to those alpha subunits of rat meprin, an enzyme previously shown to degr ade azocasein and insulin B chain but not known to degrade extracellul ar matrix components. Immunoprecipitation studies, Western blot analys es and other biochemical properties of the purified enzyme confirm tha t the distinct matrix-degrading enzyme is indeed meprin. Our data also demonstrate that meprin is the major enzyme in the renal cortex capab le of degrading components of the extracellular matrix. The demonstrat ion of this hitherto unknown function of meprin suggests its potential role in renal pathophysiology.