Plasma and liver contents of malonic aldehyde are studied one day after administration of bromobenzene to mice pretreated with a polymeric form of zinc-metaUothionein from rat liver. It is found that zinc-metallothionein injected in a dose of 1-4 mg/kg 5-10 min prior to injection of bromobenzene (2 g/kg, about 56% of LDs0) markedly lowers the malonic dialdehyde level and active toxicity of this xenobiotic. Administration of a mixture modeling Zn-metaUothionein (albumin, cysteine, and zinc) in a dose of 4 mg/kg has no appreciable effect on the malonic dialdehyde level raised after bromobenzene injection, and does not change its LDs0. It is concluded that the protective effect of exogenous zinc-metallothionein is due to its antioxidant activity, which allows for normalization of lipid peroxidation.Metallothioneins (MT) are low-molecular-weight proteins containing up to 30% cysteine and capable of binding ions of heavy metals. MT synthesis is induced by toxic influences, which raises animals' resistance to them [6]. It is thought that the antioxidant activity of MT is one of the mechanisms underlying their antitoxic effects [6]. In fact, MT preparations do inhibit lipid peroxidation (LPO) in vitro [12]. Lipid peroxidation in rodents is suppressed after induction of the synthesis of endogenous MT by heavy metals [9]. At the same time, little is known about the effect of exogenous MT on LPO and other biological processes in vivo. Zn-MT reduces the damaging effect of Cd-MT in rats [15], mitigates the acute toxicity of ethanol [1], and protects mice against radiation [2]. The aim of this study was to examine the effect of exogenous Zn-MT on plasma and liver lev-Institute of Biophysics, Russian Ministry of Health; Institute of Nutrition, Russian Academy of Medical Sciences, Moscow. {Presented by B. B. Moroz, Member of the Russian Academy of Medical Sciences) els of LPO products after the injection of bromobenzene, a compound inducing lipid peroxidation. MATERIALS AND METHODSExperiments were performed on male (CBA• B1)F 1 mice weighing 24-26 g. All solutions were injected intraperitoneally. Purification and characterization of Zn-MT from rat liver (the protein was dissolved in the standard 10 mM Tris-HC1 buffer, pH 7.4) were described elsewhere [1]. A polymeric form of Zn-MT, which is more stable in the organism, was obtained by a reported method [11]: lysine residues were cross-linked by glutaric aldehyde (Fluka), and the protein was separated from the low-molecular form on Sephadex G-75. After electrophoresis of the polymer under denaturating conditions, a wide band corresponding to a molecular weight range of 61-70 kD was obtained, which is consistent with the published data [11]. Thus, the polymeric form consisted of 8-10 Zn-MT monomers (6-7 kD) [6,11]. Mice were in-0007-4888/95/0001-0037512.50 9Plenum Publishing Corporation