The problems of chemical regulation of oxidizing stress and the search for biologically active substances with antioxidant activity are the focus of attention of researchers in different fields of experimental biology and biomedicine [11,15,16]. In physiological conditions, the oxidation-reduction processes, which cover the energy need of cells and support oxygen utilization in tissues, are controlled by regulatory systems maintaining balanced interactions between the reactions that generate the products of oxidation and antioxidizing factors. Disturbances in this interaction, accompanied with activation of free radical processes and accumulation of products of lipid peroxidation, are considered as a universal mechanism of biological membrane damage [10,20] that is the basis of some pathological processes [9,12].Investigations of the relations between oxidizing stress and the development of many diseases revealed that the endogenous antioxidative system does not provide sufficient protection for cells and tissues against the damaging effects of free radicals. Therefore, the search for new agents of inhibition of prooxidative processes and the activation of antioxidation reactions is rather warranted [8,21].Among numerous natural compounds of high biological activity, zosterin polysaccharide, which was named after the source if its isolation, the eelgrass Zostera marina , a member of the family Zosteracea, has attracted particular attention. Zosterin is a pectin with an extremely low degree of etherification [17]. Experimental studies on zosterin pectin have revealed its pharmacological effects, such as the hypocholesteremic, entherosorption, antibacterial, antiviral, antitumoral, antiulcer, and immunomodulating effects [4]. Some of these effects are accompanied by a decrease in the concentration of the products of lipid peroxidation and normalization of the parameters of the endogenous antioxidative system in the blood and liver of experimental animals [3, 5]. These data presume the available antioxidative effects of the studied polysaccharide.The objective of this study was to reveal the antioxidative activities of low-etherified pectin from the eelgrass Z. marina and compare its activities with those of drugs used in medicine as antioxidants. MATERIAL AND METHODSThe eelgrass Zostera marina was sampled from clean water areas of Peter the Great Bay, Sea of Japan. The pectin was isolated using techniques that included acid hydrolysis of raw material, extraction with ammonium oxalate, and sedimentation of pectin with ethanol [18]. The content of galacturonic acid in the pectin was determined applying the colorimetric hydroxydiphenyl method [7]. The etherification was determined by the titrimetric technique [1]. The characteristic viscosity was determined in a mixed solution of 0.05 M sodium chloride and 0.005 M sodium oxalate at a temperature of 25.0 ° C and pH of 6.0 with an Ubbelohde viscosimeter [14]. The physical and chemical parameters of the isolated polysaccharide assay were as follows: galacturonic acid con...

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