Spontaneous and radical-induced plasma membrane lipid peroxidation in differently oxidant-sensitive yeast species and its suppression by antioxidants

Protective role of mitochondrial superoxide dismutase against high osmolarity, heat and metalloid stress inSaccharomyces cerevisiae

Superoxide dismutases, both cytosolic Cu, Zn-SOD encoded by SOD1 and mitochondrial Mn-SOD encoded by SOD2, serve Saccharomyces cerevisiae cells for defense against the superoxide radical but the phenotypes of sod1A and sod2delta mutant strains are different. Compared with the parent strain and the sod1delta mutant, the sod2delta mutant shows a much more severe growth defect at elevated salt concentrations, which is partially rescued by 2 mmol/L glutathione. The growth of all three strains is reduced at 37 degrees C, the sod2delta showing the highest sensitivity, especially when cultured in air. Addition of 1 mmol/L glutathione to the medium restores aerobic growth of the sod1delta mutant but has only a minor effect on the growth of the sod2delta strain at 37 degrees C. The sod2delta strain is also sensitive to AsIIl and AsV and its sensitivity is much more pronounced under aerobic conditions. These results suggest that, unlike the Sodlp protein, whose major role is oxidative stress defense, Sod2p also plays a role in protecting S. cerevisiae cells against other stresses--high osmolarity, heat and metalloid stress.

Effect of antioxidants on Saccharomyces cerevisiae mutants deficient in superoxide dismutases

S. cerevisiae strain delta sodl lacking Cu,Zn-superoxide dismutase and delta sodl delta sod2 mutant lacking both Cu,Zn-SOD and Mn-superoxide dismutase displayed strongly reduced aerobic growth on glucose, glycerol and lactate; delta sod2 deletion had no effect on aerobic growth on glucose and largely precluded growth on glycerol and lactate. The oxygen-induced growth defects and their alleviation by antioxidants depended on growth conditions, in particular on oxygen supply to cells. Under strong aeration, vitamins A and E had a low effect, 100 mumol/L quercetin alleviated the growth defects of all three mutants while beta-carotene had no growth-restoring effect. The superoxide producer paraquat inhibited the aerobic growth of all three mutants in a concentration-dependent manner. Low concentrations of antioxidants had no effect on paraquat toxicity while higher concentrations supported the toxic effect of the agent.

Role of strategic cysteine residues in oxidative damage to the yeast plasma membrane H(+)-ATPase caused by Fe- and Cu-containing Fenton reagents

Damage caused to Saccharomyces cerevisiae SY4 plasma membrane H(+)-ATPase by Fe- and Cu-Fenton reagents was determined in secretory vesicles containing enzyme in which Cys residues were replaced singly or in pairs by Ala. Cys-221 situated in a beta-sheet domain between M2 and M3 segments, phosphorylation domain-located Cys-409 and Cys-532 situated at the ATP-binding site play a role in the inactivation. In the presence of all three residues the enzyme exhibited a certain basic inactivation, which did not change when Cys-532 was replaced with Ala. In mutants having intact Cys-532 but lacking one or both other cysteines, replacement of Cys-221 with Ala led to lower inactivation, suggesting that Cys-221 may serve as a target for metal-catalyzed oxidation and intact Cys-532 promotes this target role of Cys-221. In contrast, the absence of Cys-409 caused higher inactivation by Fe-Fenton. Cys-532 thus seems to serve as a target for Fe-Fenton, intact Cys-409 causing a conformational change that makes Cys-532 less accessible to oxidation. The mutant lacking both Cys-221 and Cys-409 is more sensitive to Fe-Fenton than to Cu-Fenton and the absence of both Cys residues thus seems to expose presumable extra Fe-binding sites. These data and those on protection by ATP, ADP, 1,4-dithiothreitol and deferrioxamine B point to complex interactions between individual parts of the enzyme molecule that determine its sensitivity towards Fenton reagents. ATPase fragmentation caused by the two reagents differed in that the Fe-Fenton reagent produced in Western blot "smears" whereas the Cu-Fenton reagent produced defined fragments.

Viability and formation of conjugated dienes in plasma membrane lipids of Saccharomyces cerevisiae, Schizosaccharomyces pombe, Rhodotorula glutinis and Candida albicans exposed to hydrophilic, amphiphilic and hydrophobic pro-oxidants

Effects of four lipid peroxidation-inducing pro-oxidants--amphiphilic tert-butyl hydroperoxide (TBHP), hydrophobic 1,1'-azobis(4-cyclohexanecarbonitrile) (ACHN), hydrophilic FeII and 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH)--on cell growth and on generation of peroxidation products in isolated plasma membrane lipids were determined in four yeast species (S. cerevisiae, S. pombe, R. glutinis and C. albicans) differing in their plasma membrane lipid composition. TBHP and ACHN inhibited cell growth most strongly, FeII and AAPH exerted inhibitory action for about 2 h, with subsequent cell growth resumption. S. cerevisiae strain SP4 was doped during growth with unsaturated linoleic (18:2) and linolenic (18:3) acids to change its resistance to lipid peroxidation. Its plasma membranes then contained some 30% of these acids as compared with some 1.3% of 18:2 acid found in undoped S. cerevisiae, while the content of (16:1) and (18:1) acids was lower than in undoped S. cerevisiae. The presence of linoleic and linolenic acids in S. cerevisiae cells lowered cell survival and increased the sensitivity to pro-oxidants. Peroxidation-generated conjugated dienes (CD) were measured in pure TBHP- and ACHN-exposed fatty acids used as standards. The CD level depended on the extent of unsaturation and the pro-oxidant used. The TBHP-induced CD production in a mixture of oleic acid and its ester was somewhat lower than in free acid and ester alone. In lipids isolated from the yeast plasma membranes, the CD production was time-dependent and decreased after a 5-15-min pro-oxidant exposure. ACHN was less active than TBHP. The most oxidizable were lipids from S. cerevisiae plasma membranes doped with linoleic and linolenic acids and from C. albicans with indigenous linolenic acid.