title: alpha2-Macroglobulin from hemolymph of the freshwater crayfish Astacus astacus.
abstract: 1. A high mol. wt proteinase inhibitor has been purified from the haemolymph of the freshwater crayfish Astacus astacus. 2. The protein is a disulphide-bonded dimer (Mr 390,000) of two identical polypeptide chains (Mr 185,000). 3. The inhibitor displays a broad specificity and protects trypsin from inhibition by soybean trypsin inhibitor and thus is similar to vertebrate alpha 2-macroglobulin. 4. The alpha 2-macroglobulin-like inhibitor from Astacus interacts with bovine trypsin in an equimolar stoichiometry thereby decreasing tryptic hydrolysis of N-benzoyl-L-arginine-ethylester to 50% residual activity. In contrast, the activity of Astacus protease, a digestive zinc proteinase from crayfish toward succinyl-alanyl-alanyl-alanyl-4-nitroanilide is inhibited almost completely. 5. Sensitivity of the inhibitor to methylamine and autolytic cleavage suggests the presence of an internal thioester bond. 6. The N-terminal amino acid sequence of Astacus alpha 2-macroglobulin is strongly related to the alpha 2-macroglobulins from Pacifastacus leniusculus (91% identity) and from the lobster Homarus americanus (72% identity). In contrast, only 25% of the residues are identical with the alpha 2-macroglobulin from the horseshoe crab Limulus polyphemus. There is also a faint similarity to human complement protein C3 and human alpha 2-macroglobulin.
authors.affiliation: Department of Physiology, University of Heidelberg, FRG.
authors.forename: W
authors.initials: W
authors.lastname: Stöcker
authors.forename: S
authors.initials: S
authors.lastname: Breit
authors.forename: L
authors.initials: L
authors.lastname: Sottrup-Jensen
authors.forename: R
authors.initials: R
authors.lastname: Zwilling
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003400:Astacoidea / Q000378:metabolism*; D003176:Complement C3 / Q000737:chemistry; D010450:Endopeptidases / Q000378:metabolism; D006458:Hemolymph / Q000737:chemistry*; D006801:Humans; D046911:Macromolecular Substances; D008744:Methylamines / Q000494:pharmacology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012689:Sequence Homology, Nucleic Acid; D000511:alpha-Macroglobulins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D003176:Complement C3; D046911:Macromolecular Substances; D008744:Methylamines; D000511:alpha-Macroglobulins; C027451:methylamine; D010450:Endopeptidases