cell biochemistry and function Cell Biochem Funct 2003; 21: 75–79. Published online 1 November 2002 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/cbf.998 Glutathione redox system, GSH-Px activity and lipid peroxidation (LPO) levels in tadpoles of R.r.ridibunda and B.viridis Levent Cavas 1 and Leman Tarhan 2 * 1 Department of Chemistry, Faculty of Arts and Sciences, University of Dokuz Eylu ¨l, 35160, _ Izmir, Turkey 2 Department of Chemistry, Faculty of Education, University of Dokuz Eylu ¨l, 35150, Buca, _ Izmir, Turkey Total glutathione (t-GSH), reduced glutathione (GSH), glutathione disulphide (GSSG) levels, t-GSH/GSSG ratio, glu- tathione peroxidase (GSH-Px) activity and lipid peroxidation (LPO) levels were investigated during the development period of a predominantly aquatic amphibian R.r.ridibunda and a predominantly terrestrial amphibian B. viridis. While t-GSH and GSH showed a similar trend, GSSG concentration increased significantly ( p < 0.05) during the larval stages in R.r.ridibunda larvae. In contrast to R.r.ridibunda larvae, there was no significant ( p > 0.05) change between 1 and 5 weeks in the t-GSH and GSH concentrations of B. viridis. t-GSH and GSH concentrations of B. viridis larvae became sharply elevated after the fifth week, GSSG levels increased 3.25-fold during the metamorphosis. The t-GSH/GSSG ratio fluctuated and the lowest t-GSH/GSSG ratios were observed at the third week for both species. GSH-Px activities for both species increased signi- ficantly ( p < 0.05) during the growing period. The highest GSH-Px activities in R.r.ridibunda and B.viridis were observed at the eighth week and they were 3.45  0.17 and 4.1  0.21 IU mg 1 , respectively. The membrane LPO levels in the R.r.ridibunda and B. viridis tadpoles significantly ( p < 0.001) decreased from 206  10.3 to 146  7.3 and from 198  9.9 to 23  1.15 nmol MDA g 1 w.w., respectively. Copyright # 2002 John Wiley & Sons, Ltd. key words — t-GSH; GSH; GSSG; GSH-Px; t-GSH/GSSG; LPO; R.r.ridibunda; B.viridis INTRODUCTION Glutathione (GSH) is a tripeptide of glutamate, cyste- ine and glycine that contains an unusual -peptide bond between glutamate and cysteine. Such a bond prevents GSH from being hydrolysed by most pepti- dases. GSH is found in most mammalian and many prokaryotic cells and is the most abundant intracellu- lar thiol (0.2–10 mM) GSH has several important cel- lular functions. GSH participates as a coenzyme and is involved in amino acid transport. It also protects many cells with high intracellular GSH levels against oxida- tive damage caused by reactive oxygen species (ROS). GSH may react with ROS non-enzymically 1–4 and also acts directly as a free radical scavenger by neutra- lizing HO  , restores damaged molecules by hydrogen donation, reduces peroxides and maintains protein thiols in the reduced state. 5 Oxidative stress may cause changes in the glutathione redox state of differ- ent tissues and thereby, increase the rate of glutathione disulphide (GSSG) production from cells. 6 Intracellu- lar reduced glutathione (GSH) is converted into oxi- dized glutathione (GSSG) by glutathione peroxidase (GSH-Px), which catalyses the reduction of perox- ides. 7 GSH-Px uses glutathione as a hydrogen donor to eliminate H 2 O 2 and to convert organic hydroperox- ides to the corresponding alcohol. 8–10 These oxygen- derived reactive oxygen species (ROS) damage the polyunsaturated fatty acids (PUFA) of membranes. Lipid peroxidation (LPO) is defined as a complex pro- cess in which oxidation of PUFA leads to membrane damage and cell death. 11,12 Amphibians metamor- phose during their development, i.e. after the embryo they experience a larval stage. Amphibian larvae use the saturated oxygen in water by uptake at their gills, but after developing their lungs, they are exposed to high concentrations of atmospheric oxygen. The Received 24 January 2002 Copyright # 2002 John Wiley & Sons, Ltd. Accepted 22 May 2002 *Correspondence to: Dr Leman Tarhan, Department of Chemistry, Faculty of Education, University of Dokuz Eylu ¨l, 35150, Buca, _ Izmir, Turkey. Tel: þ90 232 4204882-1317. Fax: þ90 232 4204855. E-mail: leman.tarhan@deu.edu.tr