title: Identification of the reactive site of ascidian trypsin inhibitor.
abstract: A trypsin inhibitor from hemolymph of the solitary ascidian, Halocynthia roretzi, has been reported to be present in two forms, ATI-I and ATI-II. ATI-I consists of a single polypeptide chain with a unique sequence of 55 amino acid residues, while ATI-II has two chains that seem to be derived from ATI-I by cleavage at the Lys16-Met17 bond [Kumazaki, T., Hoshiba, N., Yokosawa, H., and Ishii, S. (1990) J. Biochem. 107, 409-413]. ATI-II (as modified inhibitor) was proved to be produced by incubation of ATI-I (as virgin inhibitor) with a catalytic amount of bovine trypsin. The tryptic hydrolysis at the Lys16-Met17 bond in virgin inhibitor showed a maximum velocity at around pH 3.5. On the other hand, acid treatment of a complex prepared by mixing equimolar quantities of trypsin and the the modified inhibitor yielded free trypsin and the virgin inhibitor. The results of chemical analyses indicated that the Lys16-Met17 bond that had been cleaved in ATI-II was resynthesized by the acid treatment. These findings strongly suggest that the Lys16-Met17 bond is the reactive site of ATI for trypsin.
authors.affiliation: Department of Biochemistry, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo.
authors.forename: T
authors.initials: T
authors.lastname: Kumazaki
authors.forename: S
authors.initials: S
authors.lastname: Ishii
authors.forename: H
authors.initials: H
authors.lastname: Yokosawa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001197:Ascaridia / Q000737:chemistry*; D001665:Binding Sites; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D008969:Molecular Sequence Data; D014357:Trypsin / Q000378:metabolism / Q000494:pharmacology*; D014361:Trypsin Inhibitors / Q000378:metabolism*
chemical_list: D014361:Trypsin Inhibitors; D008715:Methionine; D014357:Trypsin; D008239:Lysine