Kinetic studies of the fatty acid synthetase multienzyme complex from Euglena gracilis variety bacillaris

The Mitochondrion of Euglena gracilis

In the presence of oxygen, Euglena gracilis mitochondria function much like mammalian mitochondria. Under anaerobiosis, E. gracilis mitochondria perform a malonyl-CoA independent synthesis of fatty acids leading to accumulation of wax esters, which serve as the sink for electrons stemming from glycolytic ATP synthesis and pyruvate oxidation. Some components (enzymes and cofactors) of Euglena's anaerobic energy metabolism are found among the anaerobic mitochondria of invertebrates, others are found among hydrogenosomes, the H₂-producing anaerobic mitochondria of protists.

Red blood cell glutathione peroxidase activity in female nulligravid and pregnant rats

BACKGROUND

The alterations of the glutathione peroxidase enzyme complex system occur in physiological conditions such as aging and oxidative stress consequent to strenuous exercise.

METHODS

Authors optimize the spectrophotometric method to measure glutathione peroxidase activity in rat red blood cell membranes.

RESULTS

The optimization, when applied to age paired rats, both nulligravid and pregnant, shows that pregnancy induces, at seventeen d of pregnancy, an increase of both reactive oxygen substance concentration in red blood cells and membrane glutathione peroxidase activity.

CONCLUSION

The glutathione peroxidase increase in erythrocyte membranes is induced by systemic oxidative stress long lasting rat pregnancy.

Mitochondrial trans-2-enoyl-CoA reductase of wax ester fermentation from Euglena gracilis defines a new family of enzymes involved in lipid synthesis

Under anaerobiosis, Euglena gracilis mitochondria perform a malonyl-CoA independent synthesis of fatty acids leading to accumulation of wax esters, which serve as the sink for electrons stemming from glycolytic ATP synthesis and pyruvate oxidation. An important enzyme of this unusual pathway is trans-2-enoyl-CoA reductase (EC 1.3.1.44), which catalyzes reduction of enoyl-CoA to acyl-CoA. Trans-2-enoyl-CoA reductase from Euglena was purified 1700-fold to electrophoretic homogeneity and was active with NADH and NADPH as the electron donor. The active enzyme is a monomer with molecular mass of 44 kDa. The amino acid sequence of tryptic peptides determined by electrospray ionization mass spectrometry were used to clone the corresponding cDNA, which encoded a polypeptide that, when expressed in Escherichia coli and purified by affinity chromatography, possessed trans-2-enoyl-CoA reductase activity close to that of the enzyme purified from Euglena. Trans-2-enoyl-CoA reductase activity is present in mitochondria and the mRNA is expressed under aerobic and anaerobic conditions. Using NADH, the recombinant enzyme accepted crotonyl-CoA (km=68 microm) and trans-2-hexenoyl-CoA (km=91 microm). In the crotonyl-CoA-dependent reaction, both NADH (km=109 microm) or NADPH (km=119 microm) were accepted, with 2-3-fold higher specific activities for NADH relative to NADPH. Trans-2-enoyl-CoA reductase homologues were not found among other eukaryotes, but are present as hypothetical reading frames of unknown function in sequenced genomes of many proteobacteria and a few Gram-positive eubacteria, where they occasionally occur next to genes involved in fatty acid and polyketide biosynthesis. Trans-2-enoyl-CoA reductase assigns a biochemical activity, NAD(P)H-dependent acyl-CoA synthesis from enoyl-CoA, to one member of this gene family of previously unknown function.

Isolation of a novel type-I fatty-acid synthetase from Euglena gracilis. Specific derepression in streptomycin-bleached cells

A novel, high-molecular-mass fatty-acid synthetase (FAS) complex has been isolated from streptomycin-bleached Euglena gracilis cells. The enzyme was purified 250-fold from the crude cell homogenate and subsequently migrated upon SDS/PAGE as a single band of molecular mass 270 kDa. This apparent subunit size of the purified protein contrasted with a smaller size of only 200 kDa which was exhibited by the same protein upon immunoblotting of the crude cell extract. The purified Euglena FAS complex cosediments in a sucrose density gradient with yeast FAS and, from this, both enzymes were concluded to have the same overall molecular mass of 2.3 MDa. The enzyme described in this paper appears to be a typical type-I FAS multienzyme which clearly differs from the E. gracilis FAS so far described. Instead, it appears to be organized structurally similar to the type-I FAS multienzymes of lower fungi. In vitro, the purified Euglena FAS complex synthesizes mainly palmitic acid, or its CoA ester, from acetyl CoA and malonyl CoA as substrates. The Km values for acetyl CoA and malonyl CoA are 20 microM and 31 microM, respectively. Similar to the FAS enzymes of other lower eucaryotes, the Euglena type-I FAS is a flavoprotein. In contrast to yeast FAS, however, the flavin cofactor appears to be covalently attached to the enzyme protein. By immunological techniques, the enzyme was shown to be absent in green as well as in etiolated E. gracilis cells, while being rapidly induced upon streptomycin bleaching of heterotrophically growing green cells. The data suggest an inverse correlation between organellar development and derepression of this FAS complex.

Fatty acid synthesis in mitochondria of Euglena gracilis

A malonyl-CoA-independent fatty acid synthetic system, different from the systems in other subcellular fractions, occurred in mitochondria of Euglena gracilis. The system had ability to synthesize fatty acids directly from acetyl-CoA as both primer and C2 donor using NADH as an electron donor. Fatty acids were synthesized by reversal of beta-oxidation with the exception that enoyl-CoA reductase functioned instead of acyl-CoA dehydrogenase in degradation system. A fairly high activity of enoyl-CoA reductase was found on various enoyl-CoA substrates (C4-C12) with NADH or NADPH. Three species of enoyl-CoA reductase, distinct from each other by their chain-length specificity, were found in Euglena mitochondria, and one of them was highly specific for crotonyl-CoA. It is also discussed that the mitochondrial fatty-acid synthetic system contributes to wax ester fermentation, the anaerobic energy-generating system found in the organism.

Comparison of glycerophosphate acyltransferases from Euglena chloroplasts and microsomes

The acylation of sn-glycerol 3-phosphate is a common reaction in the pathways leading to the biosynthesis of glycerol-derived phospholipids, galactolipids, and sulfolipids. Enzymes catalyzing this reaction have been solubilized from Euglena chloroplasts, microsomes, and mitochondria (B. A. Boehler and M. L. Ernst-Fonberg (1976) Arch. Biochem. Biophys. 175, 229-235; L. V. Grobovsky, S. Hershenson, and M. L. Ernst-Fonberg (1979) FEBS Lett. 102, 261-264). Some characteristics of the reactions catalyzed by the acyl-CoA:sn-glycerol-3-phosphate O-acyltransferases (EC 2.3.1.15) solubilized from chloroplasts and microsomes of Euglena have been compared. Although the two enzymes have some common features, including stimulation by bovine serum albumin and phosphatidyl choline and sensitivity to sulfhydryl-binding reagents, they differ in their stabilities and responses to salt and glycerol. They exhibit different acyl-CoA substrate dependency curves. The proportions of monoacyl sn-glycerol-3-phosphate acyltransferase activity differ in the two solubilized enzyme preparations, and different products are produced by each of the glycerophosphate acyltransferases solubilized from chloroplasts and microsomes, respectively. Neither glycerophosphate acyltransferase will use palmitoyl- or myristoyl-acyl carrier protein (ACP) as a substrate whereas both use the corresponding CoA esters. Neither is inhibited by ACP, but the enzyme from microsomes is inhibited by CoA.

Relatedness of acyl carrier proteins shown by amino acid compositions

1. Relatedness among the following carrier proteins was assessed on the basis of amino acid compositions: eight acyl carrier proteins (ACP's) associated with fatty acid synthesis, ACP's associated with citrate lyase and citramalate lyase, a biotin carboxyl carrier protein and cytochrome 552. Two independent indices of amino acid composition were used. 2. The fatty acid synthesis-associated ACP's of many organisms and the lyase-associated ACP's show a high degree of relatedness among one another. 3. The ACP's show no relatedness to biotin carboxyl carrier protein or cytochrome 552.