Patchwork‐structure serpins from silkworm (Bombyx mori) larval hemolymph

Abstract

A new serpin (serine proteinase inhibitor), having antichymotryptic activity, was isolated from silkworm, Bombyx mori, larval hemolymph and was named silkworm antichymotrypsin II (sw‐AchyII). Amino‐acid‐sequence analysis of sw‐AchyII revealed that it consisted of 375 amino acids without cysteine or glycosylated residues. sw‐AchyII formed an SDS‐undissociable complex with α‐chymotrypsin, but this complex was broken down at pH 12.5 into α‐chymotrypsin and sw‐AchyII in which the reactive site was cleaved. Amino‐acid‐sequence analysis after cleavage identified in P1‐P1′ residue at the reactive site of sw‐AchyII as Phe340‐Met341. The amino acid sequence from the amino terminus to residue 336 was completely identical to the corresponding region of sw‐AT [Takagi, H., Narumi, H., Nakamura, K. & Sasaki, T. (1990) J. Biochem. (Tokyo) 108, 372–378]. The degree of similarity between sw‐AchyII and silkworm antitrypsin (sw‐AT) from residue 337 to the carboxy terminus was only 46%. Reactive sites of both serpins were in the variable regions. Copyright © 1991, Wiley Blackwell. All rights reserved