AN OLD ENZYME WITH A NEW FUNCTION - PURIFICATION AND CHARACTERIZATION OF A DISTINCT MATRIX-DEGRADING METALLOPROTEINASE IN RAT-KIDNEY CORTEX AND 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 gel 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 trypsin and was not inhibited by tissue inhibitors of metalloproteinases indicating that it is distinct from the other matrix-degrading metalloproteinases. Unexpectedly, the amino acid sequence of the NH2-terminal and two internal peptides of the enzyme showed complete homology to those alpha subunits of rat meprin, an enzyme previously shown to degrade azocasein and insulin B chain but not known to degrade extracellular matrix components. Immunoprecipitation studies, Western blot analyses and other biochemical properties of the purified enzyme confirm that the distinct matrix-degrading enzyme is indeed meprin. Our data also demonstrate that meprin is the major enzyme in the renal cortex capable of degrading components of the extracellular matrix. The demonstration of this hitherto unknown function of meprin suggests its potential role in renal pathophysiology.