Abstract
A proline endopeptidase inhibitor was purified from rat brain cytosol by ion exchange chromatography on SP-Sephadex C-25 and repeated gel filtrations on Sephadex G-50. The purified inhibitor appeared to be homogeneous on polyacrylamide gel electrophoresis with and without sodium dodecyl sulfate and displayed no multiple forms. The inhibitor showed Mr=7000 by gel filtration and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and contained 61.6% polar amino acid residues, 3.3% aromatic amino acid residues and no tryptophan. The inhibitor was highly specific for proline endopeptidase from rat brain and hog kidney, and inhibited the enzyme competitively. It did not act on proline-specific exopeptidase such as dipeptidyl aminopeptidase IV, or on usual endopeptidases such as trypsin, elastase and plasmin, or thiol proteases such as papain and ficin.
