ATP Yield Research Articles

Optimization of glycolysis: new discussions

The concept of glycolysis optimization, first presented in Waddell (Biochemical Education 25 (1997) 204–205) and Heinrich et al. (Eur. J. Biochem. 243 (1997) 191–201), is reiterated and clarified in response to questions by Christoffersen et al. (Biochemical Education 26 (1998) 290–291). Indeed, increasing the ATP yield above 2ATP/glucose would lead to a decrease in the ATP production rate and a lower flux of material toward lactate.

Carbohydrate utilization during exercise after high-altitude acclimation: a new perspective.

At high altitude (HA), carbohydrate (CHO) is thought to be the preferred fuel because of its higher yield of ATP per mole of O2. We used indirect calorimetry and D-[6-3H]glucose infusions to determine total CHO and circulatory glucose utilization during exercise in HA-acclimated and sea level (SL) rats. We hypothesized that the percent contribution of CHO to total metabolism (VO2) is determined by exercise intensity relative to an aerobic maximum (% VO2max). HA rats run under hypoxia (FIO2 = 0.12) showed a decrease in VO2max compared with SL (67.55 +/- 1.26 vs. 89.30 +/- 1.23 ml kg-1 min-1). When exercised at 60% of their respective VO2max, both groups showed the same relative use of CHO (38 +/- 3% and 38 +/- 5% of VO2, at the beginning of exercise, in HA and SL, respectively). In both HA and SL, circulatory glucose accounted for approximately 20% of VO2, the balance was provided by muscle glycogen (approximately 18% of VO2). After 20 min at a higher intensity of 80% VO2max, 54 +/- 5% (HA) and 59 +/- 4% (SL) of VO2 was accounted for by CHO. We conclude the following: (i) the relative contributions of total CHO, circulatory glucose, and muscle glycogen do not increase after HA acclimation because the O2-saving advantage of CHO is outweighed by limited CHO stores; and (ii) relative exercise intensity is the major determinant of metabolic fuel selection at HA, as well as at SL.

Methanogenic Degradation of Polysaccharides and the Characterization of Polysaccharolytic Clostridia from Anoxic Rice Field Soil

Summary The anaerobic degradation of polysaccharides to methane via intermediary metabolites and the characteristics of some polysaccharolytic bacteria were investigated in Italian rice field soil. The addition of xylan, pectin or cellulose to slurries of anoxic rice field soil enhanced the production rates of CH 4 and CO 2 both at 15 and 30 °C (cellulose only after prolonged incubation), and resulted in the transient accumulation of H 2 , acetate, propionate and lactate. Counting of bacteria using the MPN technique indicated that xylan- and pectin-fermenting bacteria were more abundant than cellulolytic bacteria. Three gram-positive, strictly anaerobic, rod-shaped clostridia strains, RCel1, RXyl1 and RPec1 were isolated by enrichment cultures using as substrates cellulose, xylan and pectin, respectively, and characterized phylogenetically (16S rDNA sequences) and physiologically. The fermentation of cellulose by the cellulolytic strain RCell, closely related to Clostridium papyrosolvens , was investigated in more detail both at 30 °C and 15 °C, both in monoculture and in coculture with either Methanospirillum hungatei or Sporomusa ovata . The cocultures generally resulted in higher growth yields of strain RCel1 than in monoculture suggesting a better ATP yield per mol of anhydroglucose fermented. In monoculture, strain RCel1 fermented cellulose primarily to H 2 , acetate and ethanol and to smaller amounts of succinate, lactate and formate. Propionate was produced only at 15 °C. In coculture with M. hungatei , an increase in H 2 and acetate production and a decrease in lactate, ethanol, and formate production was observed. The H 2 partial pressures in the cocultures were lower than in the monoculture. In coculture with S. ovata , cellulose was fermented to acetate as main product. The steady state H 2 partial pressure in coculture with S. ovata was higher than with M. hungatei , and was lower at 15 °C than at 30 °C in both cocultures as expected from the theory. The levels of H 2 in coculture with M. hungatei were similar to those observed in rice field soil slurries. The other fermentation products of cellulose, xylan or pectin observed in bacterial cultures were also mostly the same as observed in slurries of anoxic rice field soil, but important quantitative differences remained.

Metabolism in Pyruvate Fermentation Under Various Aeration Conditions

Intracellular flux analysis was made to study the metabolism of pyruvate fermentation using Torulopsis glabrata IFO 0005 under different aeration conditions. With the fluxes calculated, key metabolic pathways were analyzed and compared in detail for cultures at various DO concentrations. Low ATP yields of many cases indicates that most energy generated was consumed by some non-biosynthesis related functions in metabolism. Total energy requirement for metabolism and intracellular redox balance were also considered.

Energy provision from glycogen, glucose, and fatty acids on adrenergic stimulation of isolated working rat hearts.

We postulated that glycogen is a significant energy substrate compared with fatty acids and glucose in response to adrenergic stimulation of working rat hearts. Oxidation rates were determined at 1-min intervals by release of 3H2O from [9,10-(3)H]oleate (0.4 mM, 1% albumin) and 14CO2 from exogenous [U-14C]glucose (5 mM) or, by a pulse-chase method, from [14C]glycogen. We estimated the 14C enrichment of glycogen metabolized at each time point to determine true rates of glycogen use. Based on the pattern of glycogen enrichment over time, glycogenolysis did not exhibit a high degree of preference for newly synthesized glycogen. Epinephrine (1 microM) increased contractile performance 86% but did not stimulate oleate oxidation. The increased energy demand was supplied by carbohydrates, initially by a burst of glycogenolysis (contributing 35% to total ATP synthesis for 5 min) and followed by delayed increase in the use of exogenous glucose (eventually contributing 29% to ATP synthesis). On the basis of the release of 14CO2 and [14C]lactate specifically from glucose or glycogen, we found that a larger portion of glycogen was oxidized compared with exogenous glucose, augmenting the yield of ATP from glycogen. Thus the heart responds to an acute increase in energy demand by selective oxidation of glycogen.

Mechanism and evolution of hypoxia-tolerance in humans.

To physiologists, the term 'adaptation' usually refers to any trait that is considered advantageous; evolutionary biologists require a more rigorous definition (restricting it to traits arising and maintained under selection). By their definition, many physiological traits may merely reflect inheritance passed on through lineage. In considering the evolution of tolerance to reduced oxygen availability, we examined the issue (of true adaptations versus simple inheritance) in pinnipeds (the two dominant groups, phocids and otariids, with varying diving capacities) and in human lineages exposed for varying generational periods to hypobaric hypoxia. Basic principles of the evolution of complex physiological systems first emerged from an analysis of the diving response. We then analyzed human responses to hypobaric hypoxia in three different lineages: lowlanders, Andean natives (Quechuas) and Himalayan natives (Sherpas). As in the pinniped example, we found 'conservative' and 'adaptable' physiological characters involved in human responses to hypoxia. Conservative characters are clearly dominant and are too numerous to outline in detail; three examples are haemoglobin oxygen-affinities, the organization of muscle into different fibre types and the brain's almost exclusive preference for glucose as a fuel. Most notably, we also found evidence for 'adaptable' characters at all levels of organization examined. At the whole-body level in Quechuas and Sherpas, we found (i) that maximum aerobic and anaerobic exercise capacities were down-regulated, (ii) that the acute effect of hypoxia (making up the energy deficit due to oxygen lack; i.e. the Pasteur effect) expected from lowlanders was blunted, and (iii) that acclimation effects were also attenuated. The biochemical behaviour of skeletal muscles was consistent with lowered reliance on glycolytic contributions to energy supply, thus improving the yield of ATP per mole of carbon fuel utilized. Heart adaptations also seemed to rely upon stoichiometric efficiency adjustments, improving the yield of ATP per mole of oxygen consumed (by using glucose in preference to fatty acids). Most of the biochemical and physiological adaptations we noted (both as acute and as acclimation responses) were similar in Sherpas and Quechuas. These two lineages have not shared a common ancestor for approximately one-third of the history of our species, so it is possible that their similar physiological traits arose independently as hypoxia defence adaptations in two different times and places in our history. As in the evolution of exquisite capacities for management of oxygen down to vanishingly low levels in diving animals, the evolution of human hypoxia-tolerance can be described in terms of how two (conservative versus adaptable) categories of physiological characters are assembled in different human lineages and how the assembly changes through generational time. More recent evidence indicating that our species evolved under 'colder, drier and higher' conditions suggests that these adaptations may represent the 'ancestral' physiological condition for humans.

How does the ratio of ATP yield from the complete oxidation of palmitic acid to that of glucose compare with the relative energy contents of fat and carbohydrate?

The authors of many recent popular textbooks of biochemistry quote values for the ‘energy content’ of triacylglcyerol and dry carbohydrate on a weight basis as well as presenting calculations for the yield of ATP obtained when a molecule of glucose, or palmitic acid, is completely oxidised to CO 2 and H 2O. By extending these calculations and computing the yield of ATP in terms of the weight of glucose or palmitic acid oxidised to CO 2 and H 2O, it can be shown that the value for the ratio of the energy content of fat to that of carbohydrate is almost identical to the ratio of the yield of ATP per gram of palmitic acid oxidised, compared with that of glucose. Therefore, the efficiency (on a per gram basis) by which energy is made available as ATP is comparable for both the oxidation of fat and carbohydrate, thus underscoring the fact that the catabolic pathways for both fat and carbohydrate ultimately use the same means of generating ATP, namely, oxidative phosphorylation.

The degradation of protein and non-starch polysaccharides from botanically diverse sources of dietary fibre by ponies as measured by the mobile bag technique

Fibrous foods are major sources of energy and protein for equids. The potentially energy yielding fraction of dietary fibre consists of non-starch polysaccharides (NSP). NSP cannot be digested by equine enzymes and in order for the animal to obtain energy from NSP it must be fermented by the gut microflora to yield volatile fatty acid. This fermentation process is less efficient in terms of yield of ATP than the digestion of starch to glucose, and is generally believed to occur solely in the large intestine. Plant protein may be associated with the NSP or the protoplast. However, horses can only utilize that protein which has been digested and absorbed in the small intestine. Thus, knowledge of the site and extent of nutrient degradation is important to enable the accurate formulation of diets for horses. Therefore in the current study the site and extent of NSP and crude protein (CP) degradation from four fibrous foods commonly given to horses in the United Kingdom were determined in caecally fistulated ponies using mobile bags.The trial was a 4 X 3 incomplete Latin square design with three caecally fistulated Welsh X pony geldings (ca. 250 kg live weight) and four botanically diverse sources of dietary fibre. The ponies were maintained on a basal diet of hay and grass nuts and water was available ad libitum. Bags (6X1 cm) of monofilament polyester mesh pore size 4 μm were filled with 350 mg of either unmolassed sugar-beet pulp (SB), hay cubes (HC), soya hulls (SH) or oat hulls : naked oats (2:1) (OH: NO), which had been ground to pass a 1-mm steel mesh. On two consecutive mornings 20 bags were introduced into the ponies via a naso-gastric tube. Each bag contained two 100 mg steel washers which enabled their capture by a magnet placed inside the caecal fistula: the cannulae were positioned just posterior to the ileo-caecal junction. Between 10 and 16 bags were recovered on the magnet, the remaining bags were allowed to continue through the hind-gut and were subsequently collected in the faeces.

The oxygen-responsive transcriptional regulator FNR of Escherichia coli: the search for signals and reactions.

The FNR (fumarate and nitrate reductase regulation) protein of Escherichia coli is an oxygen-responsive transcriptional regulator required for the switch from aerobic to anaerobic metabolism. In the absence of oxygen, FNR changes from the inactive to the active state. The sensory and the regulatory functions reside in separate domains of FNR. The sensory domain contains a Fe-S cluster, which is of the [4Fe-4S]2+ type under anaerobic conditions. It is suggested that oxygen is supplied to the cytoplasmic FNR by diffusion and inactivates FNR by direct interaction. Reactivation under anoxic conditions requires cellular reductants. In vitro, the Fe-S cluster is converted to a [3Fe-4S]+ or a [2Fe-2S]2+ cluster by oxygen, resulting in FNR inactivation. After prolonged incubation with oxygen, the Fe-S cluster is destroyed. Reassembly of the [4Fe-4S]2+ cluster might require cellular proteins, such as the NifS-like protein of E. coli. In this review, the rationale for regulation of alternative metabolic pathways by FNR and other oxygen-dependent regulators is discussed. Only the terminal reductases of respiration, and not the dehydrogenases, are regulated in such a way as to achieve maximal H+/e- ratios and ATP yields.

Theoretical approaches to the evolutionary optimization of glycolysis--chemical analysis.

In the first part of this work [Heinrich, R., Montero, F., Klipp, E., Waddell, T. G. & Melendez-Hevia, E. (1997) Eur. J. Biochem. 243, 191-201] the kinetic and thermodynamic constraints under which an optimal glycolysis must be designed have been analysed. In this second part, we present a chemical analysis of the glycolytic pathway in order to determine if its design is chemically optimized according the possibilities that a glycolytic design can have. Our results demonstrate that glycolysis in modern-day cells (from glucose to lactate) has an optimized design for maximizing the flux of ATP production, and a thermodynamic profile which guarantees a high kinetic efficiency. We also discuss some cases of paleometabolism for this pathway as alternative metabolic pathways, less optimized, that exist in some bacteria. Our analysis relates mainly to metabolism designed under constant chemical affinity (substrates and products of the pathway constant), where the target of optimization can be the flux of ATP production. We also discuss the case of an externally imposed input flux, whose target of optimization is the stoichiometric yield of ATP.

The degradation of organic matter and crude protein of four botanically diverse feedstuffs in the foregut of ponies as measured by the mobile bag technique

There is a paucity of information on the digestion and utilisation of feeds by horses. Currently, most diets are formulated according to NRC (1989) recommendations which assume digestibility coefficients: for example, a digestibility coefficient for crude protein of 0.46 is used for animals at maintenance compared with 0.55 for lactating mares. However, if the digestibility of diets is uncertain, then use of such assumed values could result in either the under- or over-supply of nutrients. Furthermore, knowledge of the site of digestion is important. For example, only dietary protein digested and absorbed in the proximal small intestine can be efficiently utilised by the horse and the digestion of carbohydrate in the foregut (in terms of ATP yield) is more efficient than its fermentation in the hind gut. Therefore, in order to formulate diets more precisely, it is important to know a) the site at which dietary components are degraded and b) the extent of this degradation. In the present study mobile bags were used to determine the extent of organic matter disappearance (OMD) and crude protein disappearance (CPD) from four botanically diverse feedstuffs in the foregut of caecally - fistulated ponies.

Environmental versus functional hypoxia/anoxia in sole Solea solea:the lactate paradox revisited

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 154:79-90 (1997) - doi:10.3354/meps154079 Environmental versus functional hypoxia/anoxia in sole Solea solea: the lactate paradox revisited Dalla Via J, van den Thillart G, Cattani O, Cortesi P The effects of hypoxia (12 and 6% air saturation), anoxia and forced exercise on intermediary metabolism were compared and the first 4 h of recovery after exhaustive exercise examined in common sole Solea solea. Intermediates of energy metabolism and lactate production were analyzed in white muscle, liver and blood. Rates of ATP production by anaerobic metabolism for the 4 different conditions were 52, 150, 1777, and 6834 µmol 100g-1 h-1, respectively. Total anaerobic ATP yield was 625, 1799, 3074, and 3132 µmol ATP 100g-1. Under hypoxia the energy consumption of the fish appeared to be depressed (i.e. below standard metabolic rate), while under anoxia the rate was at routine metabolic rate, and under forced exercise was twice the active metabolic rate. The muscle/blood lactate ratio after forced exercise was comparable to those found previously for other flatfish species; however, hypoxia exposure resulted in a completely inverse situation with blood lactate levels up to 20 mM, whereas anoxia resulted in an intermediate situation. The results challenge the present concept of lactate 'releasers' and 'non-releasers' describing the transfer of lactate from muscle tissue into the blood. It is concluded that the distinction between lacate 'releasers' and 'non-releasers' can no longer be applied on a species basis but must be related to type and intensity of the induced stress situation. Intermediary metabolism · Metabolic depression · Forced exercise · Recovery · Lactate 'releaser' and 'non-releaser' · Flatfish Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 154. Publication date: July 31, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Influence of dietary fiber consumption on oxidative metabolism and anaplerotic flux in isolated rat colonocytes.

Colonic fermentation of dietary fiber produces short-chain fatty acids which are energetic substrates for colonocytes. A high-fiber diet may lead to adaptations in colonocyte energy utilization, product formation and anaplerotic fluxes. For 2 weeks, Sprague-Dawley rats consumed diets containing 0, 150 or 300 g/kg fiber in place of digestible carbohydrate. Colonocytes were isolated; substrate oxidation and anaplerotic flux were measured. Glutamine oxidation was higher and glutamate formation was lower with increasing levels of fiber. Glucose, propionate and butyrate oxidation were not altered by diet. ATP yield from glutamine was higher in fiber-fed rats, but ATP from propionate, butyrate and glucose were not affected by the diets. Assessment of anaplerotic flux using the CO2 ratios method revealed no changes attributable to diet. The amount by which CO2 production is greater from C-1 vs C-2 of short-chain fatty acids in this system was established to be approximately 2-fold. Colonocytes use fuels in the preferential order of: glucose & butyrate > > propionate & glutamine. Because differences attributable to diet do not lead to physiologically significant alterations in anaplerotic flux or ATP yield, only minor adaptations of colonocyte oxidative metabolism occur after 2 weeks of consuming a high fiber diet.

Enhancement of marine bacterial growth by mineral surfaces

The effects of sorptive inert surfaces on growth of marine bacteria and metabolism, as well as partitioning of organic substrates, were examined in microcosms inoculated with bacterioplankton from a local salt marsh. Introduction of organic-free glass beads to a dilute seawater medium (tryptic soy broth) increased yields of ATP, a surrogate for bacterial biomass, by 187% within the entire microcosm (attached + free-living). Growth efficiencies (bacterial C/media C) were 30% for bacteria grown in microcosms with beads compared with 16% without beads. Surface enrichment increased rates of proteolytic enzyme activity and cell-specific [3H]leucine incorporation into protein by factors of 6.8 and 2.2, respectively. Scanning electron microscopy revealed obvious organic coatings on all beads after 2 h of exposure, but few strongly attached bacteria were evident, even after 40 h of exposure. Results support the hypothesis that mineral surfaces facilitate bacterial utilization of complex organic matter through physical–chemical processes that increase conversion efficiencies of labile substrate despite possible kinetic limitations. Furthermore, firm attachment by bacteria to these surfaces is apparently not a requirement to produce surface-enhanced activity.Key words: epibacteria, sorption, interfaces, hydrolytic enzymes, growth efficiency.

THE ORGANIZATION AND REGULATION OF PLANT GLYCOLYSIS.

This review discusses the organization and regulation of the glycolytic pathway in plants and compares and contrasts plant and nonplant glycolysis. Plant glycolysis exists both in the cytosol and plastid, and the parallel reactions are catalyzed by distinct nuclear-encoded isozymes. Cytosolic glycolysis is a complex network containing alternative enzymatic reactions. Two alternate cytosolic reactions enhance the pathway's ATP yield through the use of pyrophosphate in place of ATP. The cytosolic glycolytic network may provide an essential metabolic flexibility that facilitates plant development and acclimation to environmental stress. The regulation of plant glycolytic flux is assessed, with a focus on the fine control of enzymes involved in the metabolism of fructose-6-phosphate and phosphoenolpyruvate. Plant and nonplant glycolysis are regulated from the "bottom up" and "top down," respectively. Research on tissue- and developmental-specific isozymes of plant glycolytic enzymes is summarized. Potential pitfalls associated with studies of glycolytic enzymes are considered. Some glycolytic enzymes may be multifunctional proteins involved in processes other than carbohydrate metabolism.

Effects of the herbicide molinate on the metabolic activities of a degradative Streptomyces griseus strain

Abstract Cometabolic degradation of the herbicide molinate was tested using two microorganisms, Arthrobacter sp., strain M3 and Streptomyces griseus strain M2; the latter classified on the basis of the presence of the enzymatic cofactor SF‐420. The strains M3 and M2, inoculated in a basic salts medium with glucose as carbon source and added with 100 mg L‐1 of molinate, degraded respectively 35 and 51% of the herbicide in 36 days. Increasing concentrations of molinate, ranging from 50 to 200 mg L‐1 in glucose medium, did not affect the final ATP yield of the strain M2, but decreased the final growth yield and the ATP synthesis rate. Moreover, the onset of coenzyme SF‐420 synthesis was progressively delayed. In contrast, surprisingly, SF‐420 final yield and production rate were increased by progressive increasing concentrations of molinate in the mineral medium.

Glycerol fermentation by a new 1,3-propanediol-producing microorganism:Enterobacter agglomerans

According to their ability to synthesize 1,3-propanediol from glycerol, two species were isolated from the anoxic mud of a distillery waste-water digestor:Clostridium butyricum andEnterobacter agglomerans. The latter, a facultatively anaerobic gram-negative bacterium, is described for the first time as a microorganism producing 1,3-propanediol from glycerol. The products of glycerol conversion byE. agglomerans were identified using nuclear magnetic resonance. A 20-g/l glycerol solution was fermented mainly to 1,3-propanediol (0.51 mol/mol) and acetate (0.18 mol/mol). Ethanol, formate, lactate and succinate were formed as by-products. Gas production was very low; 1,3-propanediol production perfectly balanced the oxido-reduction state of the microorganism. Acetate was the predominant metabolite generating energy for growth. High-glycerol-concentration fermentations (71 g/l and 100 g/l) resulted in an increase of the 1,3-propanediol yield (0.61 mol/mol) at the expense of lactate and ethamol production. Specific rates of glycerol consumption and 1,3-propanediol and acetate production increased whereas the growth rate decreased. The decreased in ATP yield was linearly correlated with the specific rate of 1,3-propanediol production. Incomplete glycerol consumption (about 40 g/l) was systematically observed when high glycerol concentrations were used. The unbalanced oxido-reduction state, the low carbon recovery and the detection of an unknown compound by HPLC observed in these cases indicate the formation of another metabolite, which is possibly an inhibitory factor.

Toxicity of octanoic acid in Saccharomyces cerevisiae at temperatures between 8.5 and 30°C

Octanoic acid causes the inhibition of growth, decrease of the biomass yield and yield of ATP, stimulation of the specific production of ethanol in Saccharomyces cerevisiae. The toxicity of this fatty acid is higher in cells grown at temperatures below 25°C, particularly below 15.5°C, as indicated by the enhancement of the exponential constant of growth inhibition by octanoic acid with the decrease of temperature. Moreover, its presence leads to an increase of the minimum temperature for growth. The intracellular pH (pHi) of cells harvested in the mid-exponential phase of growth at temperatures within the range 8.5–30°C decreased sharply from 6.8 – 6.9 down to 5.8 – 6.2 when octanoic acid is present at concentrations of the undissociated toxic form below 14 mg 1−1. However, with more inhibitory concentrations (up to 44.5 mg 1−1) the pHi only attained 5.7 – 6.1. This may result from the decreased synthesis of succinic and acetic acids in octanoic-acid-stressed cells and from the increased buffering capacity of their cytoplasm due to the reduced internal volume. The effect of octanoic acid on intracellular acidification is nearly independent of growth temperature within the range 8.5–30°C and cannot explain the augmentation of toxicity at low temperatures.

Comparative energetics of glucose and xylose metabolism in ethanologenic recombinant Escherichia coli B.

This study compared the anaerobic catabolism of glucose and xylose by a patented, recombinant ethanologenic Escherichia coli B 11303:pLOI297 in terms of overall yields of cell mass (growth), energy (ATP), and end product (ethanol). Batch cultivations were conducted with pH-controlled stirred-tank bioreactors using both a nutritionally rich, complex medium (Luria broth) and a defined salts minimal medium and growth-limiting concentrations of glucose or xylose. The value of gamma ATP was determined to be 9.28 and 8.19 g dry wt cells/mol ATP in complex and minimal media, respectively. Assuming that the nongrowth-associated energy demand is similar for glucose and xylose, the mass-based growth yield (Yx/s, g dry wt cells/g sugar) should be proportional to the net energy yield from sugar metabolism. The value of Yx/s was reduced, on average, by about 50% (from 0.096 g/g glu to 0.51 g/g xyl) when xylose replaced glucose as the growth-limiting carbon and energy source. It was concluded that this observation is consistent with the theoretical difference in net energy (ATP) yield associated with anaerobic catabolism of glucose and xylose when differences in the mechanisms of energy-coupled transport of each sugar are taken into account. In a defined salts medium, the net ATP yield was determined to be 2.0 and 0.92 for glucose and xylose, respectively.

Growth of Methanosarcina barkeri (Fusaro) under nonmethanogenic conditions by the fermentation of pyruvate to acetate: ATP synthesis via the mechanism of substrate level phosphorylation.

A mutant of Methanosarcina barkeri (Fusaro) is able to grow on pyruvate as the sole carbon and energy source. During growth, pyruvate is converted to CH4 and CO2, and about 1.5 mol of ATP per mol of CH4 is formed (A.-K. Bock, A. Prieger-Kraft, and P. Schönheit, Arch. Microbiol. 161:33-46, 1994). The pyruvate-utilizing mutant of M. barkeri could also grow on pyruvate when methanogenesis was completely inhibited by bromoethanesulfonate (BES). The mutant grew on pyruvate (80 mM) in the presence of 2 mM BES with a doubling time of about 30 h up to cell densities of about 400 mg (dry weight) of cells per liter. During growth on pyruvate, the major fermentation products were acetate and CO2 (about 0.9 mol each per mol of pyruvate). Small amounts of acetoin, acetolactate, alanine, leucine, isoleucine, and valine were also detected. CH4 was not formed. The molar growth yield (Yacetate) was about 9 g of cells (dry weight) per mol of acetate, indicating an ATP yield of about 1 mol/mol of acetate formed. Growth on pyruvate in the presence of BES was limited; after six to eight generations, the doubling times increased and the final cell densities decreased. After 9 to 11 generations, growth stopped completely. In the presence of BES, suspensions of pyruvate-grown cells fermented pyruvate to acetate, CO2, and H2. CH4 was not formed. Conversion of pyruvate to acetate, in the complete absence of methanogenesis, was coupled to ATP synthesis. Dicyclohexylcarbodiimide, an inhibitor of H(+)-translocating ATP synthase, did not inhibit ATP formation. In the presence of dicyclohexylcarbodiimide, stoichiometries of up to 0.9 mol of ATP per mol of acetate were observed. The uncoupler arsenate completely inhibited ATP synthesis, while the rates of acetate, CO2, and H2 formation were stimulated up to fourfold. Cell extracts of M. barkeri grown on pyruvate under nonmethenogenic conditions contained pyruvate: ferredoxin oxidoreductase (0.5 U/mg), phosphate acetyltransferase (12 U/mg), and acetate kinase (12 U/mg). From these data it is concluded that ATP was synthesized by substrate level phosphorylation during growth of the M. barkeri mutant on pyruvate in the absence of methanogenesis. This is the first report of growth of a methanogen under nonmethanogenic conditions at the expense of a fermentative energy metabolism.