Amino Acid Sequence and Biological Activities of Another Kunitz-type Protease Inhibitor isolated from the Sea Anemone Anthopleura aff. xanthogrammica

Abstract

In addition to the two protease inhibitors (AXPI-I and II) previously characterized, another inhibitor (AXPI-III) has been isolated from the aqueous extract of the sea anemone Anthopleura aff. xanthogrammica by acetone precipitation, gel nitration, cation-exchange FPLC, and reverse-phase HPLC. Like AXPI-I and II, AXPI-III is a basic polypeptide and its amino acid composition is characterized by the presence of 6 half-Cys residues and the absence of Met and Trp. AXPI-III is potently inhibitory against trypsin and also considerably inhibitory against α-chymotrypsin. Both AXPI-II and III did not inhibit the binding of 125I-α-dendrotoxin to rat synaptosomal membranes, suggesting that they are not blockers of voltage-sensitive potassium channels. Analyses of the N-terminal portion and one asparaginylendopeptidase-digested fragment established the complete amino acid sequence of AXPI-III comprising 61 residues. The overall sequence homology and the conserved location of half-Cys residues confirmed that AXPI-III belongs to the Kunitz-type family.