title: Acute toxicity of vipoxin and its components: is the acidic component an "inhibitor" of PLA2 toxicity?
abstract: Vipoxin is a heterodimeric neurotoxin isolated from the venom of the Bulgarian long-nosed viper Vipera ammodytes meridionalis. Vipoxin represents a noncovalent association of two subunits - a basic and toxic phospholipase A2 enzyme, and an acidic non-enzymatic component (vipoxin's acidic component). It was postulated that the phospholipase A2 subunit was more toxic than the whole vipoxin complex and the function of the acidic component was to reduce the enzymatic and toxic activities of the basic phospholipase A2. In the present study, we report new data on the acute toxicity (LD50) of vipoxin and its individual separated components. Vipoxin LD50 (mice, i.p. and i.v.) values were found to be 0.7-1.2 mg/kg b.w. (i.p.) and 0.9-1.3 mg/kg b.w. (i.v.). The established LD50 values for the separated pure phospholipase A2 subunit are higher - 10.0-13.0 mg/kg b.w (i.p.) and 2.2-3.0 mg/kg b.w. (i.v.), i.e. the individual phospholipase A2 subunit displays less toxic activity than vipoxin, contrary to the data published in the literature. The reconstituted vipoxin complex (obtained after preliminary incubation of pure separated phospholipase A2 and acidic component showed enzyme activity and toxicity comparable to that of the native vipoxin complex. Addition of acidic component to the phospholipase A2 subunit showed a positive effect on the enzymatic activity, reaching maximal enzyme reaction rate of acidic component to phospholipase A2 molar ratio of 0.8:1 on using 4-nitro-3-octanoyloxy-benzoic acid as substrate. For the first time we showed that the acidic subunit was absolutely required for the toxic activity of vipoxin. Based on the obtained results, we assume that the function of the acidic component is to stabilize the neurotoxin's quaternary structure, required for its toxic and enzymatic activities, similarly to the role of the acidic component of crotoxin.
authors.affiliation: Sofia University "St. Kl. Ohridski", Faculty of Chemistry and Pharmacy, Department of Analytical Chemistry, Laboratory of Biocoordination and Bioanalytical Chemitsry, Sofia, Bulgaria ; Military Medical Academy, Emergency Toxicology Clinic, Sofia, Bulgaria.
authors.forename: Vasil N
authors.initials: VN
authors.lastname: Atanasov
authors.forename: Silviya
authors.initials: S
authors.lastname: Stoykova
authors.forename: Yana
authors.initials: Y
authors.lastname: Goranova
authors.forename: Mariana
authors.initials: M
authors.lastname: Mitewa
authors.forename: Svetla
authors.initials: S
authors.lastname: Petrova
keywords: acidic component; acute toxicity; phospholipase A2; vipoxin
references.citation: Eur J Biochem. 1993 Jun 1;214(2):491-6
references.pmid: 8513799
references.citation: Toxicon. 1978;16(1):37-44
references.pmid: 622724
references.citation: Biochemistry. 1993 Oct 12;32(40):10708-13
references.pmid: 8399216
references.citation: Biol Chem Hoppe Seyler. 1987 Apr;368(4):343-52
references.pmid: 3606821
references.citation: Acta Crystallogr D Biol Crystallogr. 2001 Nov;57(Pt 11):1552-9
references.pmid: 11679719
references.citation: Toxicon. 1996 Oct;34(10):1149-55
references.pmid: 8931255
references.citation: Toxicon. 1976;14(6):477-85
references.pmid: 13518
references.citation: Toxicon. 2004 Jun 1;43(7):801-10
references.pmid: 15284014
references.citation: Spectrochim Acta A Mol Biomol Spectrosc. 2003 Feb;59(3):617-27
references.pmid: 12524132
references.citation: Adv Cytopharmacol. 1979;3:231-5
references.pmid: 474296
references.citation: Farmakol Toksikol. 1978 Jun-Aug;41(4):497-502
references.pmid: 668880