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Abstract
The presence of two specific trypsin-chymotrypsin inhibitors from head parts of the rhynch-obdellid leech Theromyzon tessulatum is reported. Two proteins, anti-trypsin-chymotrypsin A (ATCA; 14636.6 ± 131 Da) and anti-trypsin-chymotrypsin B (ATCB; 14368 ± 95 Da) were purified by size exclusion and anion-exchange chromatography followed by reversed-phase HPLC. Based on amino-acid composition, N-terminal sequence determination (MELCELGQSCSRD-NPQPSNM), matrix assisted laser desorption-time of flight measurement (MALDI-TOF), trypsin mapping comparison, inhibition constant determination (Ki), and influence on amido-lytic activity of different serine proteases, it is demonstrated that ATCA and ATCB are novel and highly potent serine-protease inhibitors of trypsin and chymotrypsin (ATCA: 350 fM towards trypsin and chymotrypsin; ATCB: 400 and 75 fM towards trypsin and chymotrypsin, respectively). It is further surmised that ATCA and ATCB are linked, in that ATCB would lead to the formation of ATCA after loss of few amino acid residues.