Malic enzyme levels are increased by the activation of NADPH-consuming pathways: detoxification processes

The administration to rats of either t-butyl hydroperoxide or phenobarbital, compounds that are metabolized through detoxification processes, produces an increase in specific activity of the NADPH-consuming enzymes, glutathione reductase and NADPH-cytochrome c reductase. These compounds also produce a very significant increase in the specific activity of malic enzyme. Immunoprecipitation with a specific antibody for malic enzyme indicates that specific activity changes are the result of corresponding changes in the amounts of enzyme protein present. The administration of 1,3-bis(chloroethyl(-1-nitrosourea (a glutathione reductase inhibitor) together with t-butyl hydroperoxide abolishes any stimulation of malic enzyme activity. These results indicate that an increase in NADPH consumption induces the synthesis of malic enzyme. Alternatively, a protection of enzyme degradation cannot be rigorously excluded.     

Species-related variations in tissue antioxidant status--I. Differences in antioxidant enzyme profiles.

1. Antioxidant enzyme activity profiles in red cells of man, rabbit, quail, pig and rat have been investigated and found to exhibit striking differences. 2. No direct correlations between activities of "functionally coupled" enzymes (superoxide dismutase/catalase and glutathione peroxidase/glutathione reductase) were apparent, suggesting their independent regulation. 3. However, activities of red cell catalase and glutathione peroxidase in the various species studied were inversely correlated. 4. This was most evident in quail red cells, which showed negligible catalase activity but the highest levels of glutathione peroxidase of all the species examined. 5. A significant positive correlation between catalase and glutathione reductase activities was also demonstrated. 6. This may be relevant to the suggestion that the binding of NADPH to catalase may serve to decrease the intracellular inactivation of this reducing cofactor which may be limiting in the glutathione reductase reaction. 7. Basal levels of glutathione, which have been claimed to be limiting for the glutathione peroxidase reaction, were found to correlate positively with the activity of this enzyme in red cells. 8. Myocardial tissues also exhibited species-related differences in antioxidant enzyme profiles but these did not bear any obvious relationship to patterns observed in the corresponding red cells.     

Coding nucleotide sequence of rat liver malic enzyme mRNA

The nucleotide sequence of the mRNA for malic enzyme ((S)-malate NADP+ oxidoreductase (oxaloacetate-decarboxylating, EC 1.1.1.40) from rat liver was determined from three overlapping cDNA clones. Together, these clones contain 2078 nucleotides complementary to rat liver malic enzyme mRNA. The single open reading frame of 1761 nucleotides codes for a 585-amino acid polypeptide with a calculated molecular mass of about 65,460 daltons. The cloned cDNAs contain the complete 3'-noncoding region of 301 nucleotides for the major mRNA species of rat liver and 16 nucleotides of the 5'-noncoding region. Amino acid sequences of seven tryptic peptides (67 amino acids) from the purified protein are distributed through the single open reading frame and show excellent correspondence with the translated nucleotide sequence. The putative NADP-binding site for malic enzyme was identified by amino acid sequence homology with the NADP-binding site of the enoyl reductase domain of fatty acid synthetase.     

The characteristics of glutathione reductase distribution and activity in the liver of adult rats subjected to paraquat action in the embryonic period

Paraquat action on glutathione reductase activity and intratissue distribution in the liver of intact rats and also in the animals antenatally treated with the given herbicide was studied by some biochemical and histochemical methods. It has been ascertained that paraquat injection into intact animals promotes the increase in the intracellular enzyme level, development of glutathione reductase staining of hepatocyte nuclei, diffuse distribution of the staining along the lobe. In rats antenatally treated with paraquat acute priming does not induce glutathione reductase. In these conditions a mosaic distribution of this enzyme is observed in the hepatic tissue.     

Purification and immunological studies of glutathione reductase from rat liver. Evidence for an antigenic determinant at the nucleotide-binding domain of the enzyme

Glutathione reductase has been purified to homogeneity by a method which is an improvement of an earlier procedure (Carlberg, I. and Mannervik, B. (1975) J. Biol. Chem. 250, 5475-5480). The new steps in the purification scheme include affinity chromatography on 2',5' ADP-Sepharose 4B. Antibodies to glutathione reductase from rat liver were raised in rabbits and used for analysis of the enzyme by quantitative 'rocket' immunoelectrophoresis. Glutathione reductase from human erythrocytes, porcine erythrocytes, and calf-liver gave precipitin lines showing partial identity with the rat liver enzyme in Ouchterlony double diffusion experiments. Enzyme from spinach, yeast (Saccharomyces cerevisiae), and the photosynthetic bacterium Rhodospirillum rubrum did not give precipitates with the antibodies to the enzyme from rat liver. Titration of glutathione reductase from the different sources with antibodies confirmed the cross-reactivity of the mammalian enzymes; the human enzyme giving the strongest heterologous reaction. No reaction was observed with the enzyme from spinach, yeast, and Rhodospirillum rubrum. NADPH, NADP+, and 2',5' ADP were found to inhibit the interaction between antibodies and glutathione reductase from rat liver and human erythrocytes. NADH, glutathione, or glutathione disulfide did not protect the enzyme from reacting with the antibodies. It is concluded that glutathione reductase has an antigenic binding site for the antibodies at the pyridine nucleotide-binding site of the enzyme molecule.     

NADH-cytochrome c reductase, succinate cytochrome c reductase and phospholipids.

Phospholipid peroxidation of isolated rat liver inner mitochondrial membranes induced by either ascorbate or cysteine was accompanied by a release of flavins and coenzyme Q. A straight correlation between this release and the alteration of molecular species of phosphatidylcholine and phosphatidylethanolamine containing one saturated and one unsaturated fatty acid has been found. Peroxidation induced on molecular species of phosphatidylcholine and phosphatidylethanolamine containing only unsaturated fatty acids were accompanied by losses in enzyme activities of NADH-cytochrome c reductase and succinate cytochrome c reductase.     

Glucocorticoid-dependent induction of HMG-CoA reductase and malic enzyme gene expression by polychlorinated biphenyls in rat hepatocytes

Administration of xenobiotics to rats results in hypercholesterolemia and in the induction of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and malic enzyme. To investigate the mechanism of the induction of the enzymes by xenobiotics, the effects of xenobiotics on gene expressions for HMG-CoA reductase, malic enzyme, and cytochrome P-450 in rat liver and in cultured hepatocyte were investigated. The treatment of rats with polychlorinated biphenyls (PCB) as a xenobiotic induced mRNAs for HMG-CoA reductase and malic enzyme as well as CYP2B1/2 (cytochrome P-450b/e). Other xenobiotics, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), and chloretone, also increased HMG-CoA reductase mRNA. In an investigation of diurnal rhythm of mRNA for HMG-CoA reductase, the induction by PCB was observed in a dark period. Induced expressions of HMG-CoA reductase gene and malic enzyme gene by PCB were observed in primary cultured rat hepatocytes and showed that the action of PCB on the gene expression relating to lipid metabolism was directed on hepatocytes. The induction was observed only in hepatocytes cultured on Engelbreth-Holm-Swarm sarcoma basement membrane gel (EHS-gel), not on type I collagen, which is usually used for monolayer culture of hepatocytes. The induction of CYP2B1/2 gene expression also was observed only in the cells cultured on EHS-gel. The induction of HMG-CoA reductase and malic enzyme by PCB required dexamethasone. However, the addition of dexamethasone per se to medium containing insulin did not show an inductive effect on levels of mRNA for HMG-CoA reductase and malic enzyme. From the data of diurnal variation and hepatocyte culture experiment, HMG-CoA reductase and malic enzyme are considered to be induced by PCB through the so-called "permissive effect" of glucocorticoid.     

Purification and immunological studies of glutathione reductase from rat liver evidence for an antigenic determinant at the nucleotide-binding domain of the enzyme

Glutathione reductase has been purified to homogeneity by a method which is an improvement of an earlier procedure (Carlberg, I. and Mannervik, B. (1975) J. Biol. Chem. 250, 5475–5480). The new steps in the purification scheme include affinity chromatography on 2′,5′ ADP-Sepharose 4B. Antibodies to glutathione reductase from rat liver were raised in rabbits and used for analysis of the enzyme by quantitative ‘rocket’ immunoelectrophoresis. Glutathione reductase from human erythrocytes, porcine erythrocytes, and calf-liver gave precipitin lines showing partial identity with the rat liver enzyme in Ouchterlony double diffusion experiments. Enzyme from spinach, yeast (Saccharomyces cerevisiae), and the photosynthetic bacterium Rhodospirillum rubrum did not give precipitates with the antibodies to the enzyme from rat liver. Titration of glutathione reductase from the different sources with antibodies confirmed the cross-reactivity of the mammalian enzymes; the human enzyme giving the strongest heterologous reaction. No reaction was observed with the enzyme from spinach, yeast, and Rhodospirillum rubrum. NADPH, NADP⁺, and 2′,5′ ADP were found to inhibit the interaction between antibodies and glutathione reductase from rat liver and human erythrocytes. NADH, glutathione, or glutathione disulfide did not protect the enzyme from reacting with the antibodies. It is concluded that glutathione reductase has an antigenic binding site for the antibodies at the pyridine nucleotide-binding site of the enzyme molecule.     

Irreversible inhibition of the human placental NADP-linked 15-hydroxyprostaglandin dehydrogenase/9-ketoprostaglandin reductase by glutathione thiosulfonate

Oxidation of glutathione disulfide by a mixture of performic and hydrochloric acids leads to the formation of several compounds that are stronger inhibitors than glutathione disulfide of the placental enzyme that possess both NADP-linked 15-hydroxyprostaglandin dehydrogenase and 9-ketoprostaglandin reductase activities. The only one of these inhibitors that has been identified is glutathione thiosulfonate. The others are unstable and may include glutathione sulfinyl sulfone and glutathione disulfone. Since the enzyme appears to have a glutathione binding site in close proximity to its active site and glutathione thiosulfonate reacts with free sulfhydryl groups, the effects of this thiosulfonate on the enzyme were examined in more detail. Glutathione thiosulfonate and methyl methanethiosulfonate cause a time-dependent irreversible inhibition of both the hydroxyprostaglandin dehydrogenase and the ketoprostaglandin reductase activities, presumably by reacting with a free sulfhydryl at the prostaglandin binding site. Experiments with PGA1-glutathione show that this sulfhydryl is not necessary for the catalytic activity of the enzyme as long as the substrate can bind at the glutathione site.     

NAD+-malic enzyme. Regulatory properties of the enzyme from Ascaris suum.

The regulatory properties of the NAD-dependent malic enzyme from the mitochondria of Ascaris suum have been studied. The malate saturation curve exhibits sigmoidicity and the degree of this sigmoidicity increases as the pH is increased. Fumarate was the only compound tested that stimulated the enzyme activity, whereas oxalacetate was the most powerful inhibitor. Activation by low levels of fumarate was found to be competitive with malate. It is proposed that this stimulation has physiological significance in controlling the dismutation reaction in the parasite. The branched-chain volatile fatty acid excretion products, tiglate, 2-methylbutanoate, and 2-methylpentanoate, inhibited the enzyme activity and this inhibition was competitive with malate. The Ki values for these compounds are in the physiological range of their concentrations; therefore, it is suggested that they may aid in controlling the malic enzyme activity in vivo. Oxalacetate inhibition of malic enzyme activity was competitive with malate, and the Ki values decreased with an increase in pH. Two alternatives are proposed which could account for the lack of oxalacetate decarboxylation by the ascarid malic enzyme.     

Irreversible inhibition of the human placental NADP-linked 15-hydroxyrpostaglandin dehydrogenase/9-ketoprostaglandin reductase by glutathione thiosulfonate

Oxidation of glutathione disulfide by a mixture of performic and hydrochloric acids leads to the formation of several compounds that are stronger inhibitors than glutathione disulfide of the placental enzyme that posses both NADP-linked 15-hydroxypyrostaglandin dehydrogenase and 9-ketoprostaglandin reductase activities. The only one of these inhibitors that has been identified is glutathione thiosulfonate. The others are unstble and may include glutathione sulfinyl sulfone and glutathione disulfone. Since the enzyme appears to have a glutathione binding site in close proximity to its active site and glutathione thiosulfonate reacts with free sulfhydryl groups, the effects of this thiosulfonate on the enzyme were examined in more detail. Glutahione thiosulfonate and methyl methanethiosulfonate cause a time-dependent irreversible inhibition of both the hydroxyprostaglandin dehydrogenase and the ketoprostaglandin reductase activities, presumably by reacting with a free sulfhydryl at the prostaglandin binding site. Experiments with PGA-glutathione show that this sulfhydryl is not necessary for the catalytic activity of the enzyme as long as the substrate can bind at the glutahione site.     

An analysis of the relationships among obesity, plasma insulin and hepatic lipogenic enzymes in "viable yellow obese" mice (Avy/a).

The development of obesity, hyperinsulinemia and six hepatic lipogenic enzymes in Avy/a mice were compared to that in a/a mice. Correlation between body weight, liver weight, plasma insulin concentration and activities of hepatic enzymes was analyzed. In the Avy/a mice, body weight, liver weight and plasma insulin level increased steadily as the mice aged. In the a/a mice, the change of these three parameters was much slower. Plasma insulin concentration in a/a mice did not increase until eight months of age. Compared with a/a mice, Avy/a mice had higher 6-phosphogluconate dehydrogenase and fatty acid synthetase activities at two months of age; lower citrate cleavage enzyme, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities at three months of age; lower citrate cleavage enzyme and glucose-6-phosphate dehydrogenase and higher acetyl CoA carboxylase activities at five months of age; and higher malic enzyme, citrate cleavage enzyme and 6-phosphogluconate dehydrogenase activities at eight months of age. There were significant correlations between plasma insulin level and body weight and between plasma insulin level and the activities of malic enzyme and citrate cleavage enzyme in Avy/a mice. The correlation between body weight and malic enzyme and citrate cleavage enzyme activities disappeared after the analysis was adjusted for plasma insulin level.     

Immunohistochemical study of glutathione reductase in rat ocular tissues at different developmental stages

Glutathione, which is found in high levels in eye tissues, is involved in multiple functions, including serving as an antioxidant and as an electron donor for peroxidases. Although the activities of enzymes related to glutathione metabolism have been reported in the eye, the issue of which cells produce these proteins, where they are produced and at what levels is an important one. Glutathione reductase, an enzyme which recycles oxidized glutathione by transferring electrons from NADPH, was localized immunohistochemically in adult rat eye in this study. The reductase was distributed in the corneal and conjunctival epithelia, corneal keratocytes and endothelium, iridial and ciliary epithelia, neural retina, and retinal pigment epithelium. In addition, it was highly expressed in ganglion cells, which are responsible for transmitting photophysiological signals from the retina to the higher visual centres. To clarify the correlation of glutathione reductase expression and oxidative stress, the enzymatic activity and the level of protein expression at the pre- and postnatal stages was examined. Expression of the enzyme was detected first in the ganglion cell layer of a late prenatal stage, and appeared in the inner plexyform layer after birth. Along with an increasing differentiation between the inner nuclear and outer nuclear layers, glutathione reductase expression became detectable in the outer plexyform layer. Pigment epithelial cells were positively stained only after birth. Expression was also detected in the lens epithelium from the prenatal to early postnatal stages although its level was low in the adult lens. Collectively, these data, except for lens epithelia, suggest the pivotal role of glutathione reductase in recycling oxidized glutathione for the protection of the tissues against oxidative stress, which is caused by eye opening accompanied by the initiation of various ocular processes, such as accession of light and transduction of the photochemical signal.     

Intersubunit transfer of fatty acyl groups during fatty acid reduction

Fatty acid reduction in Photobacterium phosphoreum is catalyzed in a coupled reaction by two enzymes: acyl-protein synthetase, which activates fatty acids (+ATP), and a reductase, which reduces activated fatty acids (+NADPH) to aldehyde. Although the synthetase and reductase can be acylated with fatty acid (+ATP) and acyl-CoA, respectively, evidence for acyl transfer between these proteins has not yet been obtained. Experimental conditions have now been developed to increase significantly (5-30-fold) the level of protein acylation so that 0.4-0.8 mol of fatty acyl groups are incorporated per mole of the synthetase or reductase subunit. The acylated reductase polypeptide migrated faster on sodium dodecyl sulfate-polyacrylamide gel electrophoresis than the unlabeled polypeptide, with a direct 1 to 1 correspondence between the moles of acyl group incorporated and the moles of polypeptide migrating at this new position. The presence of 2-mercaptoethanol or NADPH, but not NADP, substantially decreased labeling of the reductase enzyme, and kinetic studies demonstrated that the rate of covalent incorporation of the acyl group was 3-5 times slower than its subsequent reduction with NADPH to aldehyde. When mixtures of the synthetase and reductase polypeptides were incubated with [3H] tetradecanoic acid (+ATP) or [3H]tetradecanoyl-CoA, both polypeptides were acylated to high levels, with the labeling again being decreased by 2-mercaptoethanol or NADPH. These results have demonstrated that acylation of the reductase represents an intermediate and rate-limiting step in fatty acid reduction. Moreover, the activated acyl groups are transferred in a reversible reaction between the synthetase and reductase proteins in the enzyme mechanism.     

Mutational analysis of parasite trypanothione reductase: acquisition of glutathione reductase activity in a triple mutant

African trypanosomes contain a cyclic derivative of oxidized glutathione, N1,N8-bis(glutathionyl)spermidine, termed trypanothione. This is the substrate for the parasite enzyme trypanothione reductase, a key enzyme in disulfide/dithiol redox balance and a target enzyme for trypanocidal therapy. Trypanothione reductase from these and related trypanosomatid parasites is structurally homologous to host glutathione reductase but the two enzymes show mutually exclusive substrate specificities. To assess the basis of host vs parasite enzyme recognition for their disulfide substrates, the interaction of bound glutathione with active-site residues in human red cell glutathione reductase as defined by prior X-ray analysis was used as the starting point for mutagenesis of three residues in trypanothione reductase from Trypanosoma congolense, a cattle parasite. Mutation of three residues radically alters enzyme specificity and permits acquisition of glutathione reductase activity at levels 10(4) higher than in wild-type trypanothione reductase.     

Plant Morphological and Biochemical Responses to Field Water Deficits: III. Effect of Foliage Temperature on the Potential Activity of Glutathione Reductase

Activity of glutathione reductase has been related to stress tolerance; however, these enzyme assays are generally conducted at 25°C. Foliage temperature varies greatly in the field in response to soil water availability and ambient conditions and this may affect enzyme response. This study was conducted to determine the effect of changing foliage temperature on glutathione reductase activity of wheat under field conditions. Wheat leaf glutathione reductase was purified and the temperature response of the enzyme was determined at 2.5°C intervals between 12.5 and 45°C. These data, in conjunction with continuous measurements of field-grown wheat foliage temperatures, were used to compare the temperature-related changes in potential glutathione reductase activities in water stressed and control plants. Assuming saturating substrate levels, the results indicate that early in the season the daily potential enzyme activity of the irrigated and stressed plants could never have reached the daily activity predicted from the 25°C (room temperature) measurements. Later in the season, the daily potential activity of the irrigated plants was lower, and the daily potential activity of the stressed plants was higher, than the activities predicted from the 25°C determinations. These results suggest that a better understanding of the regulation of plant metabolism will be obtained by linking continuous temperature measurements of plant foliage with enzyme responses to temperature.     

The NADPH consumption regulates the NADPH-producing pathways (pentose phosphate cycle and malic enzyme) in rat adipocytes

The changes in the activity of the pentose phosphate cycle and the malic enzyme produced by the activation or inhibition of different NADPH-consuming pathways have been studied. The inhibition of the fatty acid synthesis by kynurenate produced a decrease in the flux through the pentose phosphate cycle and a diminution in the malic enzyme pathway. The incubation of the adipocytes in the presence of ter-butyl-hydroperoxide, a compound which is metabolized via a NADPH-consuming pathway, produced a big increase in the pentose phosphate cycle and the malic enzyme activities. The regulation of these NADPH-producing pathways by the NADPH/NADP ratio is discussed.     

Mixed disulfide with glutathione as an intermediate in the reaction catalyzed by glutathione reductase from yeast and as a major form of the enzyme in the cell

Glutathione reductase catalyzes the reduction of glutathione disulfide by NADPH. The FAD of the reductase is reduced by NADPH, and reducing equivalents are passed to a redox-active disulfide to complete the first half-reaction. The nascent dithiol of two-electron reduced enzyme (EH(2)) interchanges with glutathione disulfide forming two molecules of glutathione in the second half-reaction. It has long been assumed that a mixed disulfide (MDS) between one of the nascent thiols and glutathione is an intermediate in this reaction. In addition to the nascent dithiol composed of Cys(45) and Cys(50), the enzyme contains an acid catalyst, His(456), having a pK(a) of 9.2 that protonates the first glutathione (residue numbers refer to the yeast enzyme sequence). Reduction of yeast glutathione reductase by glutathione and reoxidation of EH(2) by glutathione disulfide indicate that the mixed disulfide accumulates, in particular, at low pH. The reaction of glutathione disulfide with EH(2) is stoichiometric in the absence of an excess of glutathione. The equilibrium position among E(ox), MDS, and EH(2) is determined by the glutathione concentration and is not markedly influenced by pH between 6.2 and 8.5. The mixed disulfide is the principal product in the reaction of glutathione with oxidized enzyme (E(ox)) at pH 6. 2. Its spectrum can be distinguished from that of EH(2) by a slightly lower thiolate (Cys(50))-FAD charge-transfer absorbance at 540 nm. The high GSH/GSSG ratio in the cytoplasm dictates that the mixed disulfide will be the major enzyme species.     

The redox interconversion mechanism of Saccharomyces cerevisiae glutathione reductase

The changes undergone by pure yeast glutathione reductase during redox interconversion have been studied. Both the active and inactive forms of the enzyme had similar molecular masses, suggesting that the inactivation is probably due to intramolecular modification(s). The glutathione reductase and transhydrogenase activities were similarly inactivated by NADPH and reactivated by GSH, while the diaphorase activity remained unaltered during redox interconversion of glutathione reductase. These results suggest that the inactivation site could be located far from the NADPH-binding site, although interfering with transhydrogenase activity, perhaps by conformational changes. The inactivation of glutathione reductase by 0.2 mM NADPH at pH 8 was paralleled by a gradual decrease in the absorbance at 530 nm and a simultaneous increase in the absorbance at 445 nm, while the reactivation promoted by GSH was initially associated with reversal of these spectral changes. The inactive enzyme spectrum retained some absorbance between 500 nm and 700 nm, showing a shoulder at 580-600 nm. Upon treatment of the enzyme with NADPH at pH 6.5 the spectrum remained unchanged, while no redox inactivation was observed under these conditions. It is suggested that the redox inactivation could be associated with the disappearance of the charge-transfer complex between the proximal thiolate and oxidized FAD in the two-electron-reduced enzyme. The inactive enzyme was reactivated by low GSSG concentrations, moderate dithiol concentrations, and high monothiol concentrations. These results and the spectral changes described above support the hypothesis attributing the redox interconversion to formation/disappearance of an erroneous disulfide between one of the half-cystines located at the GSSG-binding site and another cysteine nearby.     

Different effects of Triton X-100, deoxycholate, and fatty acids on the kinetics of glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase

The effects of Triton X-100, deoxycholate, and fatty acids were studied on the two steps of the ping-pong reaction catalyzed by Se-dependent glutathione peroxidases. The study was carried out by analyzing the single progression curves where the specific glutathione oxidation was monitored using glutathione reductase and NADPH. While the "classic" glutathione peroxidase was inhibited only by Triton, the newly discovered "phospholipid hydroperoxide glutathione peroxidase" was inhibited by deoxycholate and by unsaturated fatty acids. The kinetic analysis showed that in the case of glutathione peroxidase only the interaction of the lipophilic peroxidic substrate was hampered by Triton, indicating that the enzyme is not active at the interface. Phospholipid hydroperoxide glutathione peroxidase activity measured with linoleic acid hydroperoxide as substrate, on the other hand, was not stimulated by the Triton concentrations which have been shown to stimulate the activity on phospholipid hydroperoxides. Furthermore a slight inhibition was apparent at high Triton concentrations and the effect could be attributed to a surface dilution of the substrate. Deoxycholate and unsaturated fatty acids were not inhibitory on glutathione peroxidase but inhibited both steps of the peroxidic reaction of phospholipid hydroperoxide glutathione peroxidase, in the presence of either amphiphilic or hydrophilic substrates. This inhibition pattern suggests an interaction of anionic detergents with the active site of this enzyme. These results are in agreement with the different roles played by these peroxidases in the control of lipid peroxide concentrations in the cells. While glutathione peroxidase reduces the peroxides in the water phase (mainly hydrogen peroxide), the new peroxidase reduces the amphyphilic peroxides, possibly at the water-lipid interface.