Isolation and characterization of guamerin, a new human leukocyte elastase inhibitor from Hirudo nipponia

A new human leukocyte elastase inhibitor was extracted and purified from a Korean native leech Hirudo nipponia. The inhibitor, called guamerin, has a molecular weight of 6,110 and shows inhibition constant (K(i)) of 8.1 x 10^{- 14} M. It is stable at a wide range of pH from 1 to 11 and heat-stable up to 90 °C. The complete amino acid sequence of guamerin reveals a cysteine-rich polypeptide of 57 amino acid residues that shows no similarity to any known elastase inhibitors but has 51% sequence homology with hirustasin. Guamerin has identical spacing of 10 cysteine residues as antistasin-type serine proteinase inhibitors, but the P1 reactive site residue is Met³⁶ instead of Arg. The neighboring sequence of the reactive site consists primarily of hydrophobic amino acid residues. Based on examinations of the target proteinases and the reactive site specificity, guamerin is a new low molecular weight protein that inhibits elastases.