title: Inhibition of thrombin and other trypsin-like serine proteinases by cyclotheonamide A.
abstract: Cyclotheonamide A (CA), a cyclic peptide isolated from the marine sponge of the genus Theonella was shown to be a slow-binding inhibitor of several trypsin-like serine proteinases. Values of 4.6 x 10(4), 4.8 x 10(4), 9.3 x 10(3), 2.1 x 10(3) and 2.7 x 10(2) M-1 s-1 were determined for the second-order rate constants for formation of CA complexes with thrombin, trypsin, plasmin, 2-chain t-PA and factor Xa, respectively. The equilibrium constant (Ki) was measured for dissociation of CA from the CA complex with human thrombin (Ki = 1.0 nM), bovine trypsin (Ki = 0.2 nM), human plasmin (Ki = 12 nM), human factor Xa (Ki = 50 nM) and human 2-chain tissue plasminogen activator (t-PA) (Ki = 40 nM). CA produces dose dependent increases in clotting time assays. The clotting time in the thrombin time, activated partial thromboplastin time and prothrombin time assays, were doubled by 1.5, 0.9 and 48 microM CA, respectively. A model for the binding of CA to the active site of thrombin is proposed.
authors.affiliation: Department of Biological Chemistry, Merck Research Laboratories, West Point, Pennsylvania 19486.
authors.forename: S D
authors.initials: SD
authors.lastname: Lewis
authors.forename: A S
authors.initials: AS
authors.lastname: Ng
authors.forename: J J
authors.initials: JJ
authors.lastname: Baldwin
authors.forename: N
authors.initials: N
authors.lastname: Fusetani
authors.forename: A M
authors.initials: AM
authors.lastname: Naylor
authors.forename: J A
authors.initials: JA
authors.lastname: Shafer
mesh_terms: D001665:Binding Sites; D001780:Blood Coagulation Tests; D065427:Factor Xa Inhibitors; D005341:Fibrinolysin / Q000037:antagonists & inhibitors; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D008958:Models, Molecular; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000494:pharmacology*; D011485:Protein Binding; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology*; D013917:Thrombin / Q000037:antagonists & inhibitors*; D010959:Tissue Plasminogen Activator / Q000037:antagonists & inhibitors; D014361:Trypsin Inhibitors / Q000494:pharmacology
chemical_list: D065427:Factor Xa Inhibitors; D010456:Peptides, Cyclic; D015842:Serine Proteinase Inhibitors; D014361:Trypsin Inhibitors; C081986:cyclotheonamide A; D013917:Thrombin; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin