title: Trypsin-kallikrein isoinhibitor K (type Kunitz) from snails (Helix pomatia). Purification and characterization.
abstract: A basic proteinase inhibitor, isoinhibitor K, was purified by SE-Sephadex C-25 column chromatography from the mixture of acid-stable and heat-stable isoinhibitors of the snail (Helix pomatia). Isoinhibitor K is homogeneous in polyacrylamide gel, cellulose acetate and polyacrylamide-dodecylsulfate electrophoresis. From the electrophoretic mobility in dodecylsulfate-polyacrylamide gel and apparent molecular weight of 6500 +/- 200 was estimated. From the amino acid composition the inhibitor consists of 58 amino acid residues. It contains three disulfide bridges, a C-terminal valine and a lysine residue at the reactive site. Isoinhibitor K inhibits the enzymes: bovine trypsin and chymotrypsin, porcine plasmin and pancreatic kallikrein, the trypsin-like component of Streptomyces griseus proteinase-pronase E, and fungi proteinase K from Tritirachium album Limber, which is only inhibited very slightly in contrast to the effect of the mixture of isoinhibitors. The inhibitory effect of isoinhibitor K against these enzymes is compared to that of the mixture or of other isoinhibitors. The following enzymes are not inhibited by isoinhibitor K: Aspergillus proteinase P and alkaline bacillus proteinase 2231 (Röhm), which both are inhibited by the mixture of isoinhibitors. Porcine elastase, bacterial proteinase N (M) (Röhm), and a trypsin-like proteinase from wheat are not inhibited, porcine acrosin and porcine serum kallikrein only to a very minor extent by the mixture of isoinhibitors. Reactive-site peptide-bond cleavage during inhibition could not be detected. Thus, the inhibitory behaviour is just as broad in specificity and as unusual as that of the trypsin-kallikrein inhibitor (Kunitz) from bovine organs. The N-terminus is blocked by pyroglutamic acid. Isoinhibitor K is the main component of the isoinhibitors secreted into the mucus and amounts to 35-40% of the mixture.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D007611:Aprotinin / Q000302:isolation & purification* / Q000494:pharmacology; D002918:Chymotrypsin / Q000037:antagonists & inhibitors; D006372:Helix, Snails / Q000032:analysis*; D007610:Kallikreins / Q000037:antagonists & inhibitors; D008970:Molecular Weight; D011402:Pronase / Q000037:antagonists & inhibitors; D011480:Protease Inhibitors; D012908:Snails / Q000032:analysis*; D014361:Trypsin Inhibitors
chemical_list: D000596:Amino Acids; D011480:Protease Inhibitors; D014361:Trypsin Inhibitors; D007611:Aprotinin; D007610:Kallikreins; D002918:Chymotrypsin; D011402:Pronase