Photosynthesis in Rhodospirillum rubrum. 3. Metabolic control of reductive pentose phosphate and tricarboxylic acid cycle enzymes

Enzymes of the reductive pentose phosphate cycle including ribulose-diphosphate carboxylase, ribulose-5-phosphate kinase, ribose-5-phosphate isomerase, aldolase, glyceraldehyde-3-phosphate dehydrogenase and alkaline fructose-1,6-diphos-phatase were shown to be present in autotrophically grown Rhodospirillum rubrum. Enzyme levels were measured in this organism grown photo- and dark heterotrophically as well. Several, but not all, of these enzymes appeared to be under metabolic control, mediated by exogenous carbon and nitrogen compounds. Light had no effect on the presence or levels of any of these enzymes in this photosynthetic bacterium.The enzymes of the tricarboxylic acid cycle and enolase were shown to be present in R. rubrum cultured aerobically, autotrophically, or photoheterotrophically, both in cultures evolving hydrogen and under conditions where hydrogen evolution is not observed. Light had no clearly demonstrable effect on the presence or levels of any of these enzymes.     

Chemolithotrophic growth and regulation of hydrogenase formation in the coryneform hydrogen bacterium strain 11/x

1. The present paper deals with the chemolithotrophic growth of a Gram-positive hydrogen bacterium strain 11/x which shows the characteristic features of some coryneform bacteria.
2. Like other hydrogen bacteria, the strain 11/x is a facultative chemolithotroph and grows on many organic substrates faster than in a mineral medium under an atmosphere of knallgas+CO₂. Fully induced, autotrophically grown cells, subcultured mixotrophically on fructose show additive growth.
3. Cell-free extracts of autotrophically grown cells are able to reduce methylene blue, dichlorophenolindophenol, phenazine methosulphate, menadione, and FMN with hydrogen. Conditions for direct NAD(P) reduction could not be found.
4. Hydrogenase is formed under autotrophic as well as mixotrophic conditions. In the latter case the rate of hydrogenase formation is diminished depending on the organic substrate. Heterotrophically grown cells do not have any detectable hydrogenase activity. For the induction of hydrogenase in those cells a nitrogen source is a prerequisite.
5. The formation of ribulose-1,5-diphosphate carboxylase and phosphoribulokinase seems to be regulated in a way similar to that of hydrogenase: the enzymes could only be detected in autotrophically and mixotrophically grown cells but not in those grown heterotrophically.

     

The metabolism of glucose by heterocysts and vegetative cells of Anabaena cylindrica

Whole filaments of autotrophically grown Anabaena cylindrica and heterocysts isolated from them will assimilate and metabolise exogenous glucose. Radiorespirometric experiments suggest the operation of the pentose phosphate pathway. Glucose-6-phosphate and 6-phosphogluconate dehydrogenase are present in heterocysts at 6–8 times the levels found in vegetative cells whereas enzymes of the reductive pentose phosphate and glycolytic pathways are barely or not detectable. Glucose-6-phosphate dehydrogenase in vegetative cells, but not in heterocysts is subject to inhibition by ribulose diphosphate.     

Regulation of the pyruvate kinase from Alcaligenes eutrophus H 16 in vitro and in vivo

The biosynthesis of the enzyme pyruvate kinase (E.C. 2.7.1.40) of Alcaligenes eutrophus (Hydrogenomonas eutropha) H 16 was influenced by the carbon and energy source. After growth on gluconate the specific enzyme activity was high while acetate grown cells exhibited lower activities (340 and 55 μmoles/min·g protein, respectively). The pyruvate kinase from autotrophically grown cells was purified 110-fold. The enzyme was characterized by homotropic cooperative interactions with the substrate phosphoenolpyruvate, the activators AMP, ribose-5-phosphate, glucose-6-phosphate and the inhibitor ortho-phosphate. In addition to phosphate ATP caused inhibition but in this case non-sigmoidal kinetics was obtained. The half maximal substrate saturation constant S_0.5 for phosphoenolpyruvate in the absence of any effectors was 0.12 mM, in the presence of 1 mM ribose-5-phosphate 0.07 mM, and with 9 mM phosphate 0.67 mM. The corresponding Hill values were 0.96, 1.1 and 2.75. The ADP saturation curve was hyperbolic even in the presence of the effectors, the K _m value was 0.14 mM ADP. When the known intracellular metabolite concentrations in A. eutrophus H 16 were compared with the regulatory sensitivity of the enzyme, it appeared that under the conditions in vivo the inhibition by ATP was more important than the regulation by the allosteric effectors.     

Starch Degradation in Synchronously Grown Chlamydomonas reinhardtii and Characterization of the Amylase

The activities of amylase and phosphorylase were monitored during the 12-hour light/dark synchronous cell cycle of autotrophically grown Chlamydomonas reinhardtii 11-32/90. The activity of amylase increased from 7.3 to 42 micromole reducing equivalents per 10⁹ cells per hour while phosphorylase increased from 43 to 214 micromole glucose 1-phosphate released per 10⁹ cells per hour between the midlight and middark periods. Cellular fractionation indicated that both enzymes were localized solely within the chloroplast. The pH optima for amylase and phosphorylase were 6.7 to 7.6 and 6.0 to 7.4, respectively. The amylase is a heat-labile α-amylase which is insensitive to ethylenetetraaecetate but inhibited by N-ethylmaleimide.     

Enzymes of the autotrophic pathway in mating partners and transconjugants of Nocardia opaca 1 b and Rhodococcus erythropolis

Enzyme activities have been measured in the partners of a bacterial mating system consisting of the hydrogen autotroph Nocardia opaca (donor and Aut^- recipient), the heterotroph Rhodococcus erythropolis (recipient) and intra- and interspecies transconjugants after growth on fructose, pyruvate and under autotrophic conditions. Specific activities of each of the enzymes hydrogenase, phosphoribulokinase and ribulosebisphosphate carboxylase were high in autotrophically grown cells of the donor and the transconjugants: they amounted to only 10% after growth on pyruvate. The recipient cells did not grow autotrophically and the enzymes mentioned were not detectable even after growth on pyruvate. Other enzymes of the Calvin cycle were constitutively formed in all strains examined.The properties of hydrogenase (K _m for NAD, R_f in gel electrophoresis) and of ribulosebisphosphate carboxylase (K _m for RuBP and R_f) were the same in the donor and transconjugant cells. The properties of glucose-6-phosphate dehydrogenase (K _m for G-6-P and mode of inhibition by ATP and phosphoenolpyruvate) were the same in the recipient and the interspecies transconjugant cells and differed from those of the donor cells. The curves of growth under autotrophic conditions in batch culture of the donor and interspecies transconjugant were almost congruent. The specific activities of hydrogenase, phosphoribulokinase and ribulosebisphosphate carboxylase increased from 40% at the beginning to 100% at the end of the exponential growth phase; these enzymes were under coordinate control.The results are in accordance with genetic studies: the genetic information for autotrophic growth is localized on a so far unidentified genetic element and is transferred en bloc from N. opaca to Aut^- mutants of the same strain or to recipient bacteria such as R. erythropolis; expression in the wild type and transconjugant cells is the same.Abbreviations G-6-P glucose-6-phosphate - 6-PG 6-phosphogluconate - FBP fructose-1,6-bisphosphate - SBP sedoheptulose-1,7-bisphosphate - RuBP ribulose-1,5-bisphosphate     

Ribulose diphosphate oxygenase. V. Presence in ribulose diphosphate carboxylase from Rhodospirillum rubrum

Ribulose-1,5-diphosphate carboxylase was purified fifteenfold from Rhodospirillum rubrum grown autotrophically under H₂ and CO₂. There was RuDP oxygenase activity associated with the carboxylase. The oxygenase had maximal activity at pH 9.4. Although these bacterial RuDP oxygenase and carboxylase activities were cold labile, activity could not be restored by treatment at 50° in the presence of Mg⁺⁺ and a sulfhydryl reagent, in contrast to results with the enzyme from eukaryotes.     

Photoproduction of hydrogen from water in hydrogenase-containing algae.

Scenedesmus obliquus and Chlorella vulgaris cells had active hydrogenase after dark anaerobic adaptation. Illumination of these algae with visible light led to an initial production of small quantities of hydrogen gas which soon ceased owing to production of oxygen by photolysis of water. The presence of oxygen-absorbing systems in a separate chamber, not in contact with the algae, gave only a slight stimulation of hydrogen production. Addition of sodium dithionite directly to the algae led to an extensive light-dependent production of hydrogen. This stimulation was due to oxygen removal by dithionite and not to its serving as an electron donor. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea, an inhibitor of photosystem II, abolished all hydrogen photoproduction. Hydrogen evolution was not accompanied by CO₂ production and little difference was noted between autotrophically and heterotrophically grown cells. Hydrogen was not produced in a photosystem II mutant of Scenedesmus even in the presence of dithionite, establishing that water was the source of hydrogen via photosystems II and I. Hydrogen production was stimulated by the presence of glucose and glucose oxidase as an oxygen-absorbing system. Oxygen inhibited hydrogen photoproduction, even if oxygen was undetectable in the gas phase, if the algal solution did not contain an oxygen absorber. It was demonstrated that under these conditions hydrogenase was still active and the inability to produce hydrogen was probably due to oxidation of the coupling electron carrier.     

Regulation of methanol metabolism in the facultative methylotroph Nocardia sp. 239 during growth on mixed substrates in batch- and continuous cultures

The regulation of methanol metabolism in Nocardia sp. 239 was investigated. Growth on mixtures of glucose or acetate plus methanol in batch cultures resulted in simultaneous utilization of the substrates. The presence of glucose, but not of acetate, repressed synthesis of the ribulose monophosphate (RuMP) cycle enzymes hexulose-6-phosphate synthase (HPS) and hexulose-6-phosphate isomerase (HPI), and methanol was used as an energy source only. Comparable results were obtained following addition of formaldehyde (fed-batch system) to a culture growing on glucose. The synthesis of the methanol dissimilatory and assimilatory enzymes in Nocardia sp. 239 thus appears to be controlled differently. Methanol and/or formaldehyde induce the synthesis of these enzymes, but under carbon-excess conditions their inducing effect on HPS and HPI synthesis is completely overruled by glucose, or metabolites derived from it. Repression of the synthesis of these RuMP cycle enzymes was of minor importance under carbon- and energy-limiting conditions in chemostat cultures. Addition of a pulse of glucose to a formaldehyde-limited (2.5 mmol l^–1 h^–1) fed-batch culture resulted in a decrease in the levels of several enzymes of methanol metabolism (including HPI), whereas the HPS levels remained relatively constant. Increasing HPS/HPI activity ratios were also observed with increasing growth rates in formaldehyde-limited chemostat cultures. The data indicate that additional mechanisms, the identity of which remains to be elucidated, are involved in controlling the levels of these C₁-specific enzymes in Nocardia sp. 239.Abbreviations HPS hexulose-6-phosphate synthase - HPI hexulose-6-phosphate isomerase - RuMP ribulose monophosphate - FBP fructose-1,6-bisphosphate - PFK 6-phosphofructokinase     

Glycerolipid biosynthesis in rat adipose tissue. Effect of polyamines on triglyceride synthesis.

Triacylglycerol formation from sn-glycerol 3-phosphate and 1,2-diacyl-sn-glycerol was markedly elevated in the presence of spermine and spermidine. This was attributed to the activation of microsomal sn-glycerol 3-phosphate acyltransferase and 1,2-diacyl-sn-glycerol acyltransferase and to the inhibition of palmitoyl-CoA hydrolase. Spermine was more effective than spermidine, and putrescine did not stimulate triacylglycerol formation. The stimulatory effect of spermine on triacylglycerol-forming enzymes was observed in the presence of Mg²⁺ and was apparent in the presence or absence of bovine serum albumin. The activation of 1,2-diacyl-sn-glycerol acyltransferase by spermine was specific, and other diacylglycerol-utilizing enzymes were not affected under these conditions. These studies demonstrate that polyamines may be important regulators of triacylglycerol formation in adipose tissue.     

Microaerophilic Cooperation of Reductive and Oxidative Pathways Allows Maximal Photosynthetic Membrane Biosynthesis in Rhodospirillum rubrum

The purple nonsulfur bacterium Rhodospirillum rubrum has been employed to study physiological adaptation to limiting oxygen tensions (microaerophilic conditions). R. rubrum produces maximal levels of photosynthetic membranes when grown with both succinate and fructose as carbon sources under microaerophilic conditions in comparison to the level (only about 20% of the maximum) seen in the absence of fructose. Employing a unique partial O₂ pressure (pO₂) control strategy to reliably adjust the oxygen tension to values below 0.5%, we have used bioreactor cultures to investigate the metabolic rationale for this effect. A metabolic profile of the central carbon metabolism of these cultures was obtained by determination of key enzyme activities under microaerophilic as well as aerobic and anaerobic phototrophic conditions. Under aerobic conditions succinate and fructose were consumed simultaneously, whereas oxygen-limiting conditions provoked the preferential breakdown of fructose. Fructose was utilized via the Embden-Meyerhof-Parnas pathway. High levels of pyrophosphate-dependent phosphofructokinase activity were found to be specific for oxygen-limited cultures. No glucose-6-phosphate dehydrogenase activity was detected under any conditions. We demonstrate that NADPH is supplied mainly by the pyridine-nucleotide transhydrogenase under oxygen-limiting conditions. The tricarboxylic acid cycle enzymes are present at significant levels during microaerophilic growth, albeit at lower levels than those seen under fully aerobic growth conditions. Levels of the reductive tricarboxylic acid cycle marker enzyme fumarate reductase were also high under microaerophilic conditions. We propose a model by which the primary “switching” of oxidative and reductive metabolism is performed at the level of the tricarboxylic acid cycle and suggest how this might affect redox signaling and gene expression in R. rubrum.     

Proteome Analyses of Strains ATCC 51142 and PCC 7822 of the Diazotrophic Cyanobacterium Cyanothece sp. under Culture Conditions Resulting in Enhanced H2 Production

Cultures of the cyanobacterial genus Cyanothece have been shown to produce high levels of biohydrogen. These strains are diazotrophic and undergo pronounced diurnal cycles when grown under N₂-fixing conditions in light-dark cycles. We seek to better understand the way in which proteins respond to these diurnal changes, and we performed quantitative proteome analysis of Cyanothece sp. strains ATCC 51142 and PCC 7822 grown under 8 different nutritional conditions. Nitrogenase expression was limited to N₂-fixing conditions, and in the absence of glycerol, nitrogenase gene expression was linked to the dark period. However, glycerol induced expression of nitrogenase during part of the light period, together with cytochrome c oxidase (Cox), glycogen phosphorylase (Glp), and glycolytic and pentose phosphate pathway (PPP) enzymes. This indicated that nitrogenase expression in the light was facilitated via higher levels of respiration and glycogen breakdown. Key enzymes of the Calvin cycle were inhibited in Cyanothece ATCC 51142 in the presence of glycerol under H₂-producing conditions, suggesting a competition between these sources of carbon. However, in Cyanothece PCC 7822, the Calvin cycle still played a role in cofactor recycling during H₂ production. Our data comprise the first comprehensive profiling of proteome changes in Cyanothece PCC 7822 and allow an in-depth comparative analysis of major physiological and biochemical processes that influence H₂ production in both strains. Our results revealed many previously uncharacterized proteins that may play a role in nitrogenase activity and in other metabolic pathways and may provide suitable targets for genetic manipulation that would lead to improvement of large-scale H₂ production.     

Regulation of the glucolytic enzymes inPseudomonas putida

Summary The synthesis of glucose catabolizing enzymes is under inductive control inPseudomonas putida. Glucose, gluconate and 2-ketogluconate are the best nutritional inducers of these enzymes. Mutants unable to catabolize gluconate or 2-ketogluconate synthesized relatively high levels of glucose dehydrogenase and gluconate-6P dehydrase activities when grown in the presence of these substrates. This identifies both compounds as true inducers of these enzymes. KDGP aldolase is induced by its substrate, as evidenced by the inability of mutant cells unable to form KDGP to produce this enzyme at levels above the basal one. A 3-carbon compound appears to be the inducer of glyceraldehyde-3P dehydrogenase. This pattern of regulation suggests that there is a low degree of coordinate control in the synthesis of the glucolytic enzymes byP. putida. This is also supported by the lack of proportionality found in the levels of two enzymes governed by the same inducers, glucose dehydrogenase and gluconate-6P dehydrase, in cells grown on different conditions.Abbrevitions P phosphate - KDGP 2-Keto-3-deoxygluconate-6-phosphate - GDH glucose dehydrogenase - GNDH gluconate dehydrogenase - GK glucokinase - GNK gluconokinase - KGK ketogluconokinase - KGR 2-Ketogluconate-6-phosphate reductase - GPDH glucose-6-phosphate dehydrogenase - GNPD gluconate-6-phosphate dehydrase - KDGPA 2-Keto-3-deoxygluconate-6-phosphate aldolase - GAPDH glyceraldehyde-3-phosphate dehydrogenase     

3-Hydroxypropionyl-coenzyme A synthetase from Metallosphaera sedula, an enzyme involved in autotrophic CO2 fixation

A modified 3-hydroxypropionate cycle has been proposed as the autotrophic CO₂ fixation pathway for the thermoacidophilic crenarchaeon Metallosphaera sedula. The cycle requires the reductive conversion of 3-hydroxypropionate to propionyl-coenzyme A (propionyl-CoA). The specific activity of the 3-hydroxypropionate-, CoA-, and MgATP-dependent oxidation of NADPH in autotrophically grown cells was 0.023 μmol min⁻¹mg protein⁻¹. The reaction sequence is catalyzed by at least two enzymes. The first enzyme, 3-hydroxypropionyl-CoA synthetase, catalyzes the following reaction: 3-hydroxypropionate + ATP + CoA → 3-hydroxypropionyl-CoA + AMP + PP_i. The enzyme was purified 95-fold to a specific activity of 18 μmol min⁻¹ mg protein⁻¹ from autotrophically grown M. sedula cells. An internal peptide sequence was determined and a gene encoding a homologous protein identified in the genome of Sulfolobus tokodaii; similar genes were found in S. solfataricus and S. acidocaldarius. The gene was heterologously expressed in Escherichia coli, and the His-tagged protein was purified. Both the native enzyme from M. sedula and the recombinant enzyme from S. tokodaii not only activated 3-hydroxypropionate to its CoA ester but also activated propionate, acrylate, acetate, and butyrate; however, with the exception of propionate, the affinities for these substrates were reduced. 3-Hydroxypropionyl-CoA synthetase is up-regulated eightfold in autotrophically versus heterotrophically grown M. sedula, supporting its proposed role during CO₂ fixation in this archaeon and possibly other members of the Sulfolobaceae family.     

The Assimilation of Acetate by Chlorella vulgaris

The acetate metabolism of autotrophically grown, acetate-adaptedand acetate-grown cells is compared. All oxidize acetate rapidlyand assimilate about half of the acetate added in short-termexperiments. Kinetic analysis of the incorporation of ¹⁴C-acetatereveals citrate as a primary product of acetate assimilationin all cells in darkness. Malate formed from acetate-I-¹⁴C byacetate-grown cells is asymmetrically labelled in a manner consistentwith a primary incorporation of acetate into malate by a malatesynthase reaction. The chief difference between autotrophic and acetate-grown cellsis the faster rate at which the latter incorporate acetate carboninto compounds outside the tricarboxylic acid cycle. In particular,incorporation into protein and carbohydrate is much faster inacetate-grown cells and it is suggested that enzymes catalysingreactions leading away from the tricarboxylic acid cycle mayincrease in activity in acetate-grown cells. Light greatly stimulates acetate incorporation into lipide andalso increases the synthesis of protein and carbohydrate.     

Mutational Analyses of Glucose Dehydrogenase and Glucose-6-Phosphate Dehydrogenase Genes in Pseudomonas fluorescens Reveal Their Effects on Growth and Alginate Production

The biosynthesis of alginate has been studied extensively due to the importance of this polymer in medicine and industry. Alginate is synthesized from fructose-6-phosphate and thus competes with the central carbon metabolism for this metabolite. The alginate-producing bacterium Pseudomonas fluorescens relies on the Entner-Doudoroff and pentose phosphate pathways for glucose metabolism, and these pathways are also important for the metabolism of fructose and glycerol. In the present study, the impact of key carbohydrate metabolism enzymes on growth and alginate synthesis was investigated in P. fluorescens. Mutants defective in glucose-6-phosphate dehydrogenase isoenzymes (Zwf-1 and Zwf-2) or glucose dehydrogenase (Gcd) were evaluated using media containing glucose, fructose, or glycerol. Zwf-1 was shown to be the most important glucose-6-phosphate dehydrogenase for catabolism. Both Zwf enzymes preferred NADP as a coenzyme, although NAD was also accepted. Only Zwf-2 was active in the presence of 3 mM ATP, and then only with NADP as a coenzyme, indicating an anabolic role for this isoenzyme. Disruption of zwf-1 resulted in increased alginate production when glycerol was used as the carbon source, possibly due to decreased flux through the Entner-Doudoroff pathway rendering more fructose-6-phosphate available for alginate biosynthesis. In alginate-producing cells grown on glucose, disruption of gcd increased both cell numbers and alginate production levels, while this mutation had no positive effect on growth in a non-alginate-producing strain. A possible explanation is that alginate synthesis might function as a sink for surplus hexose phosphates that could otherwise be detrimental to the cell.     

Protein bodies and vacuoles as lysosomes : investigations into the role of mannose-6-phosphate in intracellular transport of glycosidases in pea cotyledons

We have failed to detect the presence of mannose-6-phosphate in the oligosaccharide moiety of glycoproteins from pea (Pisum sativum L. cv Burpeeana) cotyledons using an assay system sensitive to 10 picomoles of mannose-6-phosphate. We were also unable to demonstrate any retention of glycosidase activity from pea seedlings and pea cotyledons on Sepharose-coupled phosphomannosyl receptor proteins isolated from bovine liver which were, however, able to retain phosphomannosylated hexosaminidase purified from Dictyostelium discoideum secretions. Furthermore, although Sepharose-coupled phosphomannosylated hexosaminidase from Dictyostelium was able to bind phosphomannosyl receptors from bovine liver we were unable to detect the retention of any protein from acetone powder extracts of pea seedlings or from endoplasmic reticulum-associated proteins of pea cotyledons.

Based on this collective evidence we conclude that mannose-6-phosphate does not appear to play a role in the targeting of hydrolytic enzymes from the endoplasmic reticulum to the protein bodies in pea cotyledons.

     

Repression of enzyme formation inHydrogenomonas strain H16G+ by molecular hydrogen and by fructose

The glucose-utilizing mutantHydrogenomonas strain H16G⁺ differs from the original strain H16 in having a higher specific activity of glucose-6-phosphate dehydrogenase. During incubation of the original strain or of the mutant H16G⁺ in a mineral salts/fructose-medium under an atmosphere of 80% H₂ + 20% O₂, neither growth nor formation of the enzymes of the Entner-Doudoroff system occur. Molecular hydrogen represses the formation of these enzymes even in the presence of carbon dioxide, peptone, or lactate. Under air, the formation of the enzymes of the Entner-Doudoroff pathway is not repressed by lactate nor by acetate, glutamate or pyruvate. In strain H16G⁺ fructose suppresses the adaptation to glucose; glucose does not repress the formation of a fructose permease. Fructose also suppresses adaptation to and utilization of glutamate and aspartate, but not of lactate. In cells grown either chemolithotrophically or on fructose acetyl-CoA kinase, malate synthase and isocitrate lyase are rapidly formed under air after addition of acetate; the formation of these enzymes is also completely suppressed by molecular hydrogen or fructose.     

Light modulation of the activity of carbon metabolism enzymes in the crassulacean Acid metabolism plant kalanchoë

When intact Kalanchoë plants are illuminated NADP-linked malic dehydrogenase and three enzymes of the reductive pentose phosphate pathway, ribulose-5-phosphate kinase, NADP-linked glyceraldehyde-3-phosphate dehydrogenase, and sedoheptulose-1,7-diphosphate phosphatase, are activated. In crude extracts these enzymes are activated by dithiothreitol treatment. Light or dithiothreitol treatment does not inactivate the oxidative pentose phosphate pathway enzyme glucose-6-phosphate dehydrogenase. Likewise, neither light, in vivo, nor dithiothreitol, in vitro, affects fructose-1,6-diphosphate phosphatase. Apparently the potential for modulation of enzyme activity by the reductively activated light effect mediator system exists in Crassulacean acid metabolism plants, but some enzymes which are light-dark-modulated in the pea plant are not in Kalanchoë.     

Carbon metabolism inSulfobacillus thermosulfidooxidans subsp.asporogenes, strain 41

The activities of carbon metabolism enzymes were determined in cellular extracts of the moderately thermophilic, chemolithotrophic, acidophilic bacteriumSulfobacillus thermosulfidooxidans subsp.asporogenes, strain 41, grown either at an atmospheric content of CO₂ in the gas phase (autotrophically, heterotrophically, or mixotrophically) or autotrophically at a CO₂ content increased to 5–10%. Regardless of the growth conditions, all TCA cycle enzymes (except for 2-oxoglutarate dehydrogenase), one glyoxylate bypass enzyme (malate synthase), and some carboxylases (ribulose bisphosphate carboxylase, pyruvate carboxylase, and phosphoenolpyruvate carboxylase) were detected in the cell-free extracts of strain 411. During autotrophic cultivation of strains 41 and 1269, the increase in the CO2 content of the supplied air to 5–10% resulted in the activation of growth and iron oxidation, a 20–30% increase in the cellular content of protein, enhanced activity of the key TCA enzymes (citrate synthase and aconitase), and, in strain 41, a decrease in the activity of carboxylases.