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The pyrenoid is a unique protein complex in the chloroplast stroma of most eukaryotic algae. Schiff(1) has provided some evidence that Euglena pyrenoids contain RuBisCO. Cook et al.(2) reported that the pyrenoid is recognized in the chloroplasts of synchronized cells of E. gracilis only in the first half of the light period. Recently, Kiss et al.(3) showed by immunofluorescence method that anti-spinach RuBisCO binds to the pyrenoid region of the chloroplasts of E. gracilis.

Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) changes its functioning form depending on the concentration of ribulose bisphos-phate (RuBP) in the in vitro assay (Fig. 1) [1,2]. The specific activity of the carboxylase reaction is very different among the three forms. Binding of RuBP to the regulatory sites of RuBisCO has been inferred to cause the change of the form.

The thiomethyl group of S-adenosylmethionine is often recycled as methionine from methylthioadenosine. The corresponding pathway has been unravelled in Bacillus subtilis. However methylthioadenosine is subjected to alternative degradative pathways depending on the organism. This work uses genome in silico analysis to propose methionine salvage pathways for Klebsiella pneumoniae, Leptospira interrogans, Thermoanaerobacter tengcongensis and Xylella fastidiosa. Experiments performed with mutants of B. subtilis and Pseudomonas aeruginosa substantiate the hypotheses proposed. The enzymes that catalyze the reactions are recruited from a variety of origins. The first, ubiquitous, enzyme of the pathway, MtnA (methylthioribose-1-phosphate isomerase), belongs to a family of proteins related to eukaryotic intiation factor 2B alpha. mtnB codes for a methylthioribulose-1-phosphate dehydratase. Two reactions follow, that of an enolase and that of a phosphatase. While in B. subtilis this is performed by two distinct polypeptides, in the other organisms analyzed here an enolase-phosphatase yields 1,2-dihydroxy-3-keto-5-methylthiopentene. In the presence of dioxygen an aci-reductone dioxygenase yields the immediate precursor of methionine, ketomethylthiobutyrate. Under some conditions this enzyme produces carbon monoxide in B. subtilis, suggesting a route for a new gaseous mediator in bacteria. Ketomethylthiobutyrate is finally transaminated by an aminotransferase that exists usually as a broad specificity enzyme (often able to transaminate aromatic aminoacid keto-acid precursors or histidinol-phosphate). A functional methionine salvage pathway was experimentally demonstrated, for the first time, in P. aeruginosa. Apparently, methionine salvage pathways are frequent in Bacteria (and in Eukarya), with recruitment of different polypeptides to perform the needed reactions (an ancestor of a translation initiation factor and RuBisCO, as an enolase, in some Firmicutes). Many are highly dependent on the presence of oxygen, suggesting that the ecological niche may play an important role for the existence and/or metabolic steps of the pathway, even in phylogenetically related bacteria. Further work is needed to uncover the corresponding steps when dioxygen is scarce or absent (this is important to explore the presence of the pathway in Archaea). The thermophile T. tengcongensis, that thrives in the absence of oxygen, appears to possess the pathway. It will be an interesting link to uncover the missing reactions in anaerobic environments.

Light perception by the plant photoreceptor phytochrome requires the tetrapyrrole chromophore phytochromobilin (P Phi B), which is covalently attached to a large apoprotein. Arabidopsis mutants hy1 and hy2, which are defective in P Phi B biosynthesis, display altered responses to light due to a deficiency in photoactive phytochrome. Here, we describe the isolation of the HY2 gene by map-based cloning. hy2 mutant alleles possess alterations within this locus, some of which affect the expression of the HY2 transcript. HY2 encodes a soluble protein precursor of 38 kD with a putative N-terminal plastid transit peptide. The HY2 transit peptide is sufficient to localize the reporter green fluorescent protein to plastids. Purified mature recombinant HY2 protein exhibits P Phi B synthase activity (i.e., ferredoxin-dependent reduction of biliverdin IX alpha to P Phi B), as confirmed by HPLC and by the ability of the bilin reaction products to combine with apophytochrome to yield photoactive holophytochrome. Database searches and hybridization studies suggest that HY2 is a unique gene in the Arabidopsis genome that is related to a family of proteins found in oxygenic photosynthetic bacteria.

Difference spectra taken at -196°C were given to confirm that glycolate oxidation by Euglena mitochondria is linked to the electron transport system with the production of ATP. In feeding experiments with 1-14C-glycolate on E. gracilis cells having glycolate dehydrogenase only in mitochondria, greater parts of the taken-up radioactivity were excreted as 14CO2 and greater parts of the remaining were distributed to the amino acid and protein fractions, mainly as glycine and serine. Presence of ammonium decreased 14CO2 evolution and augmented incorporation and distribution to protein of label. Exhaustion of nitrogen source stopped glycolate uptake. Deficiency of nitrogen source repressed glycolate dehydrogenase most extensively among the enzymes involved in the glycolate pathway. The mechanism of regulation of the glycolate metabolism by nitrogen source is discussed.

SUMMARY: Assimilation of fatty acids, fatty alcohols and sugars by Euglena gracilis Z was investigated with or without illumination. Propionate, butyrate, valeriate, hexanoate, myristate, palmitate, ethanol, propanol, lauryl alcohol, tridecanol and myristyl alcohol supported considerable growth. The assimilation of propionate, valeriate, palmitate, butanol, lauryl alcohol and myristyl alcohol were strictly light-dependent. The photoassimilation of myristyl alcohol was saturated by lower light intensity than photosynthesis and was not completely inhibited by a photosynthetic inhibitor, suggesting involvement of a photoreaction other than photosynthesis in the photoassimilation. D-Glucose, D-fructose, D-galactose, D-xylose, D-glyceraldehyde and glycerol also supported growth. Disaccharides were not used as the carbon source for growth. The difference in the mechanism of photoassimilation between myristyl alcohol and D-galactose is discussed.

An improved method was devised to purify ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) with high specific activity (2.1 mumol of CO2 fixed/mg protein/min) from Euglena gracilis Z. The purified enzyme stored at -80 degrees C required treatment with dithiothreitol for full activity. The dithiothreitol-treated RuBisCO was activated by 12 mM NaHCO3 and 20 mM MgCl2, and the activated state was stable at least for 60 min in the presence of 4 mM ethylenediaminetetraacetate. The form of inorganic carbon fixed by the Euglena enzyme was CO2, as for the plant enzymes. The carboxylase reaction proceeded linearly with time for at least 8 min. The optimum pH for this reaction was 7.8 to 8.0. The carboxylase activity increased with increasing temperature up to 50 degrees C. The activation energy for the carboxylation reaction was 10.0 kcal/mol. The Michaelis constants of Euglena RuBisCO were 30.9 microM for CO2, 560 microM for O2, and 10.5 microM for ribulose 1,5-bisphosphate. Mathematical comparison between the photosynthesis rate predicted from these enzymatic properties and the observed rate suggested that there is no CO2-concentrating mechanism in E. gracilis.

The mechanism of induction of glycolate excretion by aminooxyacetate (AOA) during photosynthesis in Euglena gracilis Z has been studied enzymologically and metabolically. AOA inhibited glutamate: glyoxylate aminotransferase competitively with glutamate with Ki’s of 0.7 and 9.5 μm. Glycolate dehydrogenase and NADPH: glyoxylate reductase were also competitively inhibited by AOA with glycolate and glyoxylate, respectively. The Ki℉s were 1.2 and 0.4 mm, respectively. These inhibitions of the glycolate pathway enzymes could not be the immediate cause of the induction of the excretion. Intracellular concentrations of glycolate and glyoxylate were 10 and 3 nmol/mg chlorophyll in photosynthesizing Euglena. Addition of AOA to the cells caused increases of both metabolites to 13 and 7 nmol/mg chlorophyll, respectively. Glycolate dehydrogenase was strongly inhibited by glyoxylate competitively with glycolate. The Ki was 10 μm, less than one-fifteenth of the Km of glycolate dehydrogenase for glycolate. These results ...

In our preceding work ( A. Yokota, Y. Nakano, and S. Kitaoka, 1978, Agric. Biol. Chem . 42 , 121–129 ), extensive decarboxylation of glycolate carboxyl carbon during its metabolism in Euglena gracilis suggested occurrence of a metabolic pathway of glycolate different from that of higher C 3 plants. In the present report, we establish the Euglena glycolate pathway from characteristics of the decarboxylation of the carboxyl carbon and from the metabolic fate of hydroxymethyl carbon of glycolate. The ratio of the decarboxylation of the carboxyl carbon of glycolate to the total metabolized carbon increased with increasing metabolic rate in an asymptotic fashion. Thus, the ratio was 20% at the metabolic rate of 0.05 nmol of glycolate/10 6 cells/min, but it was over 60% at the rate of more than 0.35 nmol/10 6 cells/min after 2 min of incubation. Metabolic products were also changed depending on the rate of metabolism of glycolate; glycine was the main product at the low rate of glycolate metabolism and the contribution of glycine was reversed by the increased contribution of evolved CO 2 at the high rates. At the metabolic rate of 1.5 nmol of glycolate/10 6 cells/min, the rate of the decarboxylation was 1.0 nmol of CO 2 /10 6 cells/min, which could not be explained by the extremely low activity of glycine synthase in Euglena . Experiments with [2- 14 C]glycolate showed that exogenously added formate and methionine caused accumulation of radioactive formate. Based on these results, we have proposed that the glycolate metabolism of E. gracilis consists of glycine and formate pathways and that the relative contribution of both pathways to the glycolate metabolism depends on the metabolic rate of glycolate.

In contrast to reported fact, the air-grown cells of Euglena gracilis z were found to excrete glycolate into the surrounding medium, when placed in an atmosphere of 100% O2 under illumination at 20000 lux at the same rate of the 5% CO2-grown cells, but with a lag phase of about 30 min. The lag was eliminated by lowering intracellular CO2 concentration in the air-grown cells.

The mechanism for decarboxylating the carboxyl carbon of glycolate was studied in Euglena gracilis Z, which liberates more than 70% of the carboxyl carbon as CO(2) during glycolate metabolism.In the isolated mitochondria of E. gracilis, glycolate was oxidized to glyoxylate, 25% of which was aminated to glycine, with the remaining unchanged in the presence of glutamate; in the absence of the amino donor, glyoxylate was not changed. Irrespective of the presence or absence of the amino donor, no decarboxylation took place in Euglena mitochondria. In Euglena chloroplasts glyoxylate was actively decarboxylated by the action of hydrogen peroxide generated by the reaction of a Mn(2+)-dependent NADPH oxidase. This enzyme was purified 120-fold over the crude extract and some of its properties studied. Oxidation of one molecule of NADPH was accompanied by the formation of one molecule of H(2)O(2); the NADPH oxidation was not attributable to the action of l-ascorbate peroxidase, the sole peroxidase present in E. gracilis. Specific participation of chloroplasts and mitochondria in glycolate metabolism is discussed.

The half-saturating concentration of ribulose 1, 5-bisphosphate carboxylase/oxygenase (RuBisCO) from Euglena gracilis Z for CO2 in its activation by CO2 in the presence of a saturating concentration of MgCl2 (Ka) was measured by analyzing the partial reversible inactivation of the fully activated enzyme in the medium with dilute CO2. The Ka of the Euglena enzyme was 12.5 μM. The Ka values were 6.3 μM for the enzyme from soybean, 10.8 μM from maize, 23.3 μM from Scenedesmus obliquus, and 20.8 μM from Anabaena 7120. The activated state of Euglena RuBisCO was stabilized by 6-phosphogluconate, fructose 1, 6-bisphosphate, and 3-phosphoglycerate in the medium containing low concentrations of CO2. Both fructose 6-phosphate and ATP stimulated inactivation in the medium. NADPH not only stabilized the activated state of the enzyme, but also enhanced the enzyme activity over the full activity measured in the absence of NADPH. NADP+ did not nullify the effects of NADPH on the activation at all. The physiological significance of the effects of these photosynthetic metabolites on the activated state of Euglena RuBisCO is discussed.

Isocitrate lyase (ICL) was highly purified from cotyledons of dark-grown pumpkin ( Cucubita maxima Kuri Nankin) seedlings by rapid means, and a method was devised to determine glyoxylate using the enzyme in combination with yeast isocitrate dehydrogenase (NADP + ). The enzymic properties of both enzymes were adequate for determination of varying concentrations of glyoxylate. The intracellular content of glyoxylate in Euglena gracilis Klebs strain Z Pringsheim growing photosynthetically in air was determined to be 2.0 nmol mg −1 chlorophyll using this method.

The streptomycin-bleached, non-photosynthetic mutant of Euglena gracilis contained NADH-glyoxylate reductase, NADPH-glyoxylate reductase, glutamate-glyoxylate aminotransferase and serine-glyoxylate aminotransferase, in addition to glycolate dehydrogenase. Most activities of NADH- and NADPH-glyoxylate reductases and 75% of glutamate-glyoxylate aminotransferase activity in the crude homogenate were recovered in mitochondria.The mutant cells grown under illumination contained three times as high glycolate dehydrogenase activity as the dark-grown cells. Illumination on the dark-grown cells caused an increase in activity to the level of the light-grown cells. Light at 420nm wavelength was most effective for inducing the enzyme. The enzyme induced by illumination was the mitochondrial one and the specific activity increased 4-fold after illumination for 3 days; the rate of the increase was almost equal to the ratio of the rate of glycolate uptake from incubation medium by the light-grown mutant to that of the d...

As is the case with spinach ribulose bisphosphate carboxylase/oxygenase (Rubisco), [14C]carboxyarabinitol bisphosphate (CABP) bound to purified Chlorella Rubisco with a molar ratio of unity to large subunit of the enzyme. The concentration of binding sites in extracts of photosynthetic organisms was determined by reacting the extracts with [14C]-carboxypentitol bisphosphate (CPBP) and precipitating the resultant Rubisco-[14C]CABP complex with a combination of polyethylene glycol-4000 and MgCl2. Plots of the relationship between concentrations of [14C] CPBP in the reaction mixture and the precipitated [14C]CPBP gave a straight line and the concentration of binding sites were estimated by extrapolation to zero [14C]CPBP since the dissociation constant of CABP with Rubisco is 10−11 molar. Spinach, pea, and soybean leaves contained 6.4 to 6.8 milligrams Rubisco per milligram chlorophyll, corresponding to 92 to 97 ribulose bisphosphate-binding sites per milligram chlorophyll. The Rubisco content of sunflower and wheat leaves was 5.3 to 5.5 milligrams per milligram chlorophyll. The concentrations in C4 plants were not uniform and corn and Panicum miliaceum leaves contained 3 and 7 milligrams Rubisco per milligram chlorophyll. The Rubisco content of green algae was one-fifth to one-sixth that of C3 plant leaves and was affected by the CO2 concentration during growth. The content of Euglena and blue-green algae is also reported.

Euglena gracilis grew with propionate as the sole carbon source under illumination but not in the dark. The metabolic pathway of propionate was determined in E. gracilis growing under illumination. Labeled propionate was first recovered in the amino acid fraction and gradually transferred to protein and paramylon with a lapse in incubation time. In the amino acid fraction aspartic acid was most densely labeled initially, followed by glutamic acid indicating that propionate is metabolized via succinate. The result agreed with the radiorespirometric pattern of specifically labeled propionates: 1-C>2-C = 3-C. E. gracilis contained propionyl-CoA carboxylase, but not α-hydroxyglutarate synthase. The reaction product of the enzyme was identified as methylmalonyl-CoA. The enzyme activity increased in the log phase when propionate in growth medium was actively utilized for growth. From these results we have concluded that illuminated Euglena metabolizes propionate through propionyl-CoA and methylmalonyl-CoA to tr...

E. gracilis grown on air with illumination contained glycolate dehydrogenase both in mitochondria and microbodies while that grown on the air containing 5 % CO2 with illumination contained the enzyme only in mitochondria with half an activity. Transfer of cells grown on air with illumination to 5% CO2 or nitrogen atmosphere or to darkness caused disappearance of the enzyme activity in microbodies remaining it only in mitochondria. E. gracilis grown heterotrophically on various carbon sources, except glutamate in single, contained glycolate dehydrogenase only in mitochondria. The enzyme in microbodies is apparently associated with photorespiration while the mitochondrial enzyme with the glycolate metabolism in this organelle, which has functions not related to photorespiration or photosynthesis.

Illumination of the dark-grown Euglena gracilis, both the wild-green type and a permanently bleached mutant, for 4 hr at 2,000 lux caused about 6-fold increase of the cellular content of total l-ascorbic acid. The increase was mainly due to an increase of reduced-form l-ascorbic acid. From the action spectrum only blue light was found to be effective for the increase. Darkening stopped the increase and reillumination started a renewed increase. The activity of l-gulono-γ-lactone dehydrogenase, catalyzing the last step of l-ascorbic acid biosynthesis, was also increased two fold by illumination for 2 hr, and was changed in parallel to that of the cellular content of l-ascorbic acid depending on the presence or absence of illumination. The augmentation of l-ascorbic acid formation was markedly inhibited by various inhibitors and uncouplers, but not by dichlorophenyldimethylurea. The results in sum suggest that the light-dependent increase of l-ascorbic acid formation in E. gracilis is not primarily associat...

The amino acid sequence deduced from the open reading frame designated sll0755 in Synechocystis sp. PCC 6803 is similar to the amino acid sequences of thioredoxin peroxidases from other organisms, In the present study, we found that a recombinant SLL0755 protein that was expressed in Escherichia coli mas able to reduce H2O2 and tertiary butyl hydroperoxide with thioredoxin from E. coli as the electron donor, Targeted disruption of open reading frame sll0755 in Synechocystis sp, PCC 6803 cells completely eliminated the H2O2-dependent and tertiary butyl hydroperoxide-dependent photosynthetic evolution of oxygen and the electron flow in photosystem II. These results indicate that the product of open reading frame sll0755 is a thioredoxin peroxidase whose activities are coupled to the photosynthetic electron transport system in Synechocystis sp. PCC 6803, (C) 1999 Federation of European Biochemical Societies.

Drought-tolerant wild watermelon accumulates high levels of citrulline in the leaves in response to drought conditions. In this work, the hydroxyl radical-scavenging activity of citrulline was investigated in vitro. The second-order rate constant for the reaction between citrulline and hydroxyl radicals was found to be 3.9×109 M−1 s−1, demonstrating that citrulline is one of the most efficient scavengers among compatible solutes examined so far. Moreover, citrulline effectively protected DNA and an enzyme from oxidative injuries. Liquid chromatography-mass spectrometry analysis revealed that at least four major products were formed by the reaction between citrulline and hydroxyl radicals. Activities of metabolic enzymes were not inhibited by up to 600 mM citrulline, indicating that citrulline does not interfere with cellular metabolism. We reasoned, from these results, that citrulline contributes to oxidative stress tolerance under drought conditions as a novel hydroxyl radical scavenger.

Scope Human thioredoxin‐1 (hTrx‐1) is a defensive protein induced by various stresses and exerts antioxidative and anti‐inflammatory effects. Previously, we described a transplastomic lettuce overexpressing hTrx‐1 that exerts a protective effect against oxidative damage in a pancreatic β‐cell line. In this study, we treated diabetic mice (Akita mice) with exogenous hTrx‐1 and evaluated the effects. Methods and results Treatment with drinking water and single applications of exogenous hTrx‐1 did not influence the feeding, drinking behavior, body weight, blood glucose, or glycosylated hemoglobin (HbA1c) levels in Akita mice. However, chronic administration of a 10% hTrx‐1 lettuce‐containing diet was associated with a significant reduction from the baseline of HbA1c levels compared with mice fed a wild‐type lettuce‐containing diet. It also resulted in an increased number of goblet cells in the small intestine, indicating that mucus was synthesized and secreted. Conclusion Our results revealed that the administration of an hTrx‐1 lettuce‐containing diet improves the baseline level of HbA1c in Akita mice. This effect is mediated through goblet cell proliferation and possibly related to protection against postprandial hyperglycemia by mucus, which results in the improvement of blood glucose control. These findings suggest that the hTrx‐1 lettuce may be a useful tool for the continuous antioxidative and antidiabetic efficacies of the hTrx‐1 protein., Administration of an hTrx‐1 lettuce‐containing diet improves the baseline level of HbA1c in Akita mice. This effect is mediated through goblet cell proliferation in the small intestine and possibly related to protection against postprandial hyperglycemia by mucus, which results in the improvement of blood glucose control. These findings suggest that the hTrx‐1 lettuce may be a useful tool for the continuous antioxidative and antidiabetic efficacies of the hTrx‐1 protein.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzes the reactions of carboxylation and oxygenation of ribulose-1,5-bisphosphate. These reactions require that the active site should be closed by a flexible loop (loop 6) of the large subunit. Rubisco from a red alga, Galdieria partita, has the highest specificity for carboxylation reaction among the Rubiscos hitherto reported. The crystal structure of unactivated Galdieria Rubisco has been determined at 2.6 Å resolution. The electron density map reveals that a sulfate binds only to the P1 anion-binding site of the active site and the loop 6 is closed. Galdieria Rubisco has a unique hydrogen bond between the main chain oxygen of Val332 on the loop 6 and the ϵ-amino group of Gln386 of the same large subunit. This interaction is likely to be crucial to understanding for stabilizing the loop 6 in the closed state and to making a higher affinity for anionic ligands.

Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) acts at the branching point of photosynthetic carbon reduction and oxidation cycles (1). The properties of the enzyme and the CO2 and O2 concentrations around the enzyme decide the metabolic fate of photosynthetically fixed carbon, namely whether the carbon is directed to sugar synthesis or to the glycol-ate pathway to be released as CO2 (2).

Euglena gracilis showed a typical photoassimilation of propionate when cultured on propionate as a sole carbon source. While the acid is metabolized by the methylmalonyl-coenzyme A (CoA) pathway under illumination, supporting growth of Euglena ( K. Hosotani, A. Yokota, Y. Nakano, and S. Kitaoka, 1980, Agr. Biol. Chem.44, 1097–1103 ), it does not allow the protozoon to grow in the dark although it was actively taken up and metabolized. Kinetics of incorporation of radioactivity of labeled propionate, trapping effect of exogenous lactate in the incorporation of labeled propionate and radiorespirometric pattern revealed that propionate was metabolized by the lactate pathway in Euglena in the dark. Enzymes involved in the lactate pathway were located in mitochondria. The reason why Euglena can not grow on propionate in the dark is explained by the failure of producing C4 dicarboxylic acids essential for biosynthesis of amino acids and sugars, like the mitochondrial oxidation of fatty acids in higher animals. The Euglena cells cultured in the dark contained enzymes of both methylmalonyl-CoA and lactate pathways, but lack of photosynthetically generated ATP has been suggested to force Euglena to select the less-ATP-requiring but futile pathway.

The form of inorganic carbon accumulated in Euglena gracilis cells was determined. Euglena cell protein bound 0.96 nmol CO2/mg protein. The binding of CO2 was by the formation of protein carbamate as indicated by acid lability of the protein-CO2 complex, stimulation of complex formation by high ionic strength and the carbamate resonance in 13C-NMR spectrum. The protein carbamate could also be isolated from photosynthesizing Euglena. The formation of the carbamate required light energy fixed photosynthetically.

The nonenzymatic reaction of glyoxylate and H2O2 was measured under physiological conditions of the pH and concentrations of reactants. The reaction of glyoxylate and H2O2 was secondorder, with a rate constant of 2.27 l mol(-1) s(-1) at pH 8.0 and 25° C. The rate constant increased by 4.4 times in the presence of Zn(2+) and doubled at 35°C. We propose a mechanism for the reaction between glyoxylate and H2O2. From a comparison of the rates of H2O2 decomposition by catalase and the reaction with glyoxylate, we conclude that H2O2 produced during glycolate oxidation in peroxisomes is decomposed by catalase but not by the reaction with glyoxylate, and that photorespiratory CO2 originates from glycine, but not from glyoxylate, in C3 plants. Simulation using the above rate constant and reported kinetic parameters leads to the same conclusion, and also makes it clear that alanine is a satisfactory amino donor in the conversion of glyoxylate to glycine. Some serine might be decomposed to give glycine and methylene-tetrahydrofolate; the latter is ultimately oxidized to CO2. In the simulation of the glycolate pathway of Euglena, the rate constant was high enough to ensure the decarboxylation of glyoxylate by H2O2 to produce photorespiratory CO2 during the glycolate metabolism of this organism.

Culture of the green alga Chlamydomonas reinhardtii in the medium containing sodium selenite caused the activity of ascorbate peroxidase to disappear and the appearance of glutathione peroxidase. The induced maximum activity of glutathione peroxidase reached 350 micromole (milligram chlorophyll hour)(-1) under assay conditions used. The enzymic properties of the selenite-induced glutathione peroxidase closely resembled those of animal glutathione peroxidase that contains selenium.