1Malaysian Journal of Biochemistry and Molecular Biology (2008) 16(1), 1-10Review ArticleSnake Venom L-Amino Acid Oxidases and Their PotentialBiomedical ApplicationsNget-Hong Tan and Shin-Yee FungDepartment of Molecular Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia Author for correspondence: Prof. Dr. Nget-Hong Tan,Department of Molecular Medicine, Faculty of Medicine,University of Malaya, 50603 Kuala Lumpur. Tel: 603-79674912Fax: 603-79674957 E-mail: tanngethong@yahoo.com.sgAbstractL-amino acid oxidase (LAAO) occurs widely in snake venoms. The enzyme is highly specific for L-amino acids, and generally hydrophobic amino acids are the best substrates. LAAO is a flavoprotein consisting of two identical subunits, each with a molecular mass of approximately 60 kDa. The purified enzymes are glycoproteins with 3-4% carbohydrate. Deglycosylation of the enzyme did not alter the enzymatic activity but appeared to alter its pharmacological activities. The amino acid sequences of snake venom LAAOs showed a high degree of homology. X-ray structural analysis of LAAO revealed a dynamic active site and the presence of 3domains: a FAD-binding domain, a substrate-binding domain and a helical domain. LAAOs were reported to exhibit moderate lethal toxicity. Recent studies showed that LAAOs are multifunctional enzymes exhibiting edema-inducing, platelet aggregation inducing or inhibiting, apoptotic inducing as well as anti-bacterial, anti-coagulant and anti-HIV effects. These effects are mostly mediated by the H 2O 2 liberated in the oxidation process but direct interactions between LAAO and the target cells may play an important role.High resolution X-ray structure of the enzyme revealed the presence of a channel that would direct the H 2O 2 product to the exterior surface of the protein, near the glycan moiety at Asn 172. The glycan moiety was thought to be involved with LAAO-target cell interaction. This may explain the ability of LAAO to localize H 2O 2 to the targeted cells. A better understanding of the pharmacological actions of LAAOs will facilitate the application of snake venom LAAOs in the design of anti-cancer and anti-HIV drugs as well as drugs for the treatment of infectious diseases caused by parasites such as leishmaniasis.Keywords: L-amino acid oxidase, snake venomIntroductionL-Amino acid oxidase (L-amino acid:O 2 oxidoreductase,E.C. 1.4.3.2.) is a flavoenzyme that catalyzes the oxidative deamination of an L-amino acid to form the corresponding α-ketoacid and ammonia: RCH(NH 3+)COO - + O 2 + H 2O +RCOCOO - + NH 4+ + H 2O 2L-Amino acid oxidase (LAAO) occurs widely in nature [1] and snake venoms are perhaps the richest sources of the enzyme. Snake venom LAAOs are generally very active and have been used widely in preparation of α-keto acids because of their chemo- and stereospecificity [2, 3].α-Keto acids of essential amino acids are useful nutraceuticals as well as therapeutic agents for certain diseases. Recently, snake venom LAAO has become an interesting object for biomedical studies because of its antimicrobial, anti-HIV, anticoagulant, platelet aggregation-inducing and inhibiting, apoptotic-inducing as well as anti-cancer activities. Snake venom LAAO is recognized as a multifunctional protein with promising biomedical application. Several reviews on snake venom L-amino acid oxidases have been published [1, 4-9].LAAO Assay MethodsMany methods of LAAO assay are available [1]. The O 2 electrode technique has been widely used, particularly in kinetic studies. A commonly used spectrophotometric method was described by Bergmeyer, which measuredthe rate of oxidation by measuring the rate of formation of color complex between the hydrogen peroxide produced and o-dianisidine [10]. Based on the same principle, a spectrophotometric microplate assay has been developed suitable for processing large numbers of samples [11].Occurrence in Snake VenomsLAAO can be found in venoms from most genera [12].The richest sources of LAAO are the crotalid venoms.The enzyme usually constitutes 1-4% of the venom by weight but in Calloselasma rhodostoma (Malayan pit viper)it constitutes up to 30% by weight of the dried venom [8].V enoms from mamba and sea snakes either contain no or trace amount of L-amino acid oxidase activity.Purification of Snake Venom LAAOsSince 1990s, many authors have reported the purification and characterization of LAAOs from various snake venoms (Table 1). In some snake venoms, the enzymes present were in many isoforms. Hayes and Wellner, for example, reported that there were at least 18isoforms of the LAAO in Crotalus adamanteus venom,and that glycosylation contributes to the microheterogeneity
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