title: Inhibition of human platelet aggregation by L-amino acid oxidase purified from Naja naja kaouthia venom.
abstract: L-Amino acid oxidase (LAO) widely exists in snake venoms. Purification of LAO from the Naja naja kaouthia (monocellate cobra) venom has been reported (Tan and Swaminathan, 1992), but its structural characterization and physiological function remained to be determined. The function of snake venom LAOs in hemostasis, especially their effect on platelet aggregation, has been controversial. We determined the N-terminal amino acid sequence of the N. n. kaouthia LAO named K-LAO to be DDRRSPLEECFQQNDYEEFLEIAKNGLKKTxNPKHVXxV (38 residues). The protein data base search revealed that the enzyme had high similarities with other snake venom LAOs. Further, platelet aggregation studies revealed that K-LAO functionally did not induce platelet aggregation in a platelet-rich plasma system, but that it inhibited platelet aggregation induced by agonists such as ADP, collagen and ristocetin in a dose-dependent manner. K-LAO diminished platelet aggregation more intensely under low than high shear stress. This inhibitory activity of K-LAO on either ristocetin-induced or shear-induced platelet aggregation was quenched by addition of catalase. These results indicate that K-LAO functions as an inhibitor to platelet aggregation through the formation of hydrogen peroxide. The enzyme may contribute to the development of a severe hematological disorder due to cobra envenomation.
authors.affiliation: Department of Blood Transfusion Medicine, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8522, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Sakurai
authors.forename: H
authors.initials: H
authors.lastname: Takatsuka
authors.forename: A
authors.initials: A
authors.lastname: Yoshioka
authors.forename: T
authors.initials: T
authors.lastname: Matsui
authors.forename: M
authors.initials: M
authors.lastname: Suzuki
authors.forename: K
authors.initials: K
authors.lastname: Titani
authors.forename: Y
authors.initials: Y
authors.lastname: Fujimura
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000328:Adult; D000594:Amino Acid Oxidoreductases / Q000302:isolation & purification / Q000633:toxicity*; D000595:Amino Acid Sequence; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects*; D003094:Collagen / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004546:Elapid Venoms / Q000633:toxicity*; D017815:Elapidae / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D066298:In Vitro Techniques; D050830:L-Amino Acid Oxidase; D008969:Molecular Sequence Data; D010974:Platelet Aggregation / Q000187:drug effects*; D012310:Ristocetin / Q000494:pharmacology; D020539:Sequence Analysis, Protein
chemical_list: D004546:Elapid Venoms; D012310:Ristocetin; D000244:Adenosine Diphosphate; D003094:Collagen; D000594:Amino Acid Oxidoreductases; D050830:L-Amino Acid Oxidase