Isolation and Characterisation of a Low Molecular Weight Inhibitor (of Chymotrypsin and Human Granulocytic Elastase and Cathepsin G) from Leeches

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Abstract
Two protein proteinase inhibitors were isolated and purified from the leech Hirudo medicinalis by means of gel filtration and ion-exchange chromatography. They inhibit chymotrypsin, subtilisin and the granulocytic neutral proteases elastase and cathepsin G. They proved to be homogeneous in polyacrylamide and dodecylsulfate [SDS] gel electrophoresis and by end group analysis; only threonine was found as N-terminal amino acid residue using the dansylation technique. These inhibitors, termed eglins, are stable in neutral and weakly acid (pH 3) solutions and resist non-specific proteolysis. From the amino acid compositions, a MW of 6600-6800 is calculated for both inhibitory proteins, which is in good agreement with a value of about 6000 estimated by SDS electrophoresis. The eglins contain an unusually large amount of hydrophobic amino acid residues but no methionine, isoleucine or, a rarity, cysteine residues or disulfide bridges. To our knowledge, the eglins are the 1st examples of proteinase inhibitors of the protein type not stabilized by disulfide bridges.

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