THE EFFECT OF CARBON DIOXIDE TENSION ON THE METABOLISM OF CEREBRAL CORTEX AND MEDULLA OBLONGATA

Manometric measurements were made of oxygen uptake (Q _OO2) and aerobic lactic acid output (Q_G) by slices of cerebral cortex and medulla oblongata of the cat in the presence of mixtures of 1, 5, and 20 volumes per cent of carbon dioxide in oxygen. The concentrations of NaHCO₃ and NaCl in the medium were varied to maintain constant pH and sodium ion concentrations. The calcium ion concentration was 0.0002 M. At pH 7.5 under these conditions, an increase in carbon dioxide from 1 per cent to 5 per cent doubled the Q_G of both tissues but did not alter Q _OO2; an increase from 5 per cent to 20 per cent carbon dioxide had no further effect on Q_G in either tissue or Q _OO2 of cortex, but did depress the Q _OO2 of medulla. At pH 8.1, an increase in carbon dioxide from 1 per cent to 5 per cent raised the Q _OO2 and Q_G of cortex by about 60 per cent. Measurements at low oxygen tension carried out previously in phosphate medium were repeated in bicarbonate medium to obtain data for the combined output of lactic acid and carbon dioxide (Q_A). When the oxygen in the gas phase was decreased from 95 to 3 volumes per cent, the lactic acid output as measured colorimetrically increased by 114 mg./gm. in cortex and by 8 mg./gm. in medulla; Q_A increased from 12.3 to 13.5 in cortex and decreased from 5.1 to 3.8 in medulla.     

Ethanol production with Zymomonas mobilis with synthetic medium in batch operation

Ethanol was produced with Zymomonas mobilis Z6 (ATCC 29191), in batch culture with synthetic medium on glucose as substrate and in the presence of aspartate. The concentrations of glucose, phosphate, ammonium, ethanol and dissolved O₂ and CO₂ in the medium and O₂ and CO₂ in the outlet gas as well as the cell mass by culture fluorescence were measured on-line. Cell mass, glucose and aspartate concentrations were measured off-line. In the presence of a sufficient amount of aspartate, the ethanol inhibition effect can be reduced considerably. However, the improvement with yeast extract is more incisive. The relationship between the intensity of culture fluorescence and cell mass concentration is linear, if sufficient aspartate is present.List of Symbols ASP kg/m³ aspartate concentration - CTR kg/(m³ · h) CO₂ transfer rate - N, NH₄ kg/m³ nitrogen concentration from NH ₄ ⁺ - P kg/m³ product (ethanol) concentration - p% product (ethanol) yield - PO₄ kg/m³ phosphate concentration - Q _E kg/(kg · h) specific ethanol production rate - kg/(kg · h) specific nitrogen uptake rate from NH ₄ ⁺ - Q _P kg/(kg · h) specific phosphate uptake rate - Q _s kg/(kg · h) specific substrate (glucose) uptake rate - S kg/m³ glucose concentration - S _O kg/m³ initial glucose concentration - Y _x/s kg/kg yield coefficient - h^–1 specific growth rate     

Metabolic changes during substrate shifts in continuous cultures of the yeast Candida boidinii variant 60

Summary Substrate shift experiments in chemostat cultures with either methanol or glucose as carbon source were performed with the yeast Candida boidinii variant 60. At low dilution rates of 0.064 h^–1 the culture may be easily shifted from methanol to glucose medium and back again to methanol. From these experiments it can be seen that glucose does not give rise to any catabolite inhibition of alcohol oxidase. Alcohol oxidase and formaldehyde dehydrogenase seem to be regulated by a repression-derepression mechanism, as small basal activities of both these enzymes can still be measured during growth on glucose. On the other hand, formate dehydrogenase activity is completely absent in the presence of glucose. This kind of regulation seems to favor the smooth switch from growth on glucose to methanol metabolism.With methanol or glucose, growth yields (Y_S) of 0.3 and 0.35, respectively may be obtained, and oxygen consumption (Q_{O 2}) is much higher in methanol cultures than in glucose-grown cells. Accordingly, the RQ values during growth on methanol decrease to about 0.5. Based on the yield coefficient of 0.3, it is possible to calculate that 38% of the methanol consumed must be incorporated into biomass, whereas 62% of the methanol is oxidized to CO₂. The corresponding RQ of 0.56 could not be experimentally ascertained.The activities of three mitochondrial enzymes were found to be higher in methanol-grown cells than in cells from glucose cultures. The low activites of enzymes for the phosphogluconate route in methanol-grown cells indicates that a cyclic oxidation of formaldehyde via hexose phosphate to CO₂ cannot be of great importance for methanol metabolism.List of Symbols D 1/h Dilution rate - 1/h Specific growth rate - Q_{CO 2} mmol/g·h Specific CO₂ production rate - Q_{O 2} mmol/g·h Specific O₂ comsumption rate - Q_S g/g·h Specific substrate consumption rate - RQ ./. Respiratory quotient (Q_{CO 2}/Q_{O 2}) - S_O g/l Substrate concentration in the feeding medium - $#x0073;$#x0304 g/l Substrate concentration in the fermentor - $#x0078;$#x0304 g/l Biomass in the fermentor - Y_{O 2} g/mmol O₂ Biomass yield on oxygen - Y_S g/g Biomass yield on carbon source     

Estimation of Trichoderma QM 9414 biomass and growth rate by indirect means

Trichoderma QM 9414 was aerobically grown on glucose as the sole carbon and energy sources in a chemostat culture. The specific rates of glucose consumption (Q_G), oxygen consumption (Q), and carbon dioxide production (Q) at the steady state were measured to estimate the growth and maintenance requirements. From the results it was estimated that 2 mol adenosine triphosphate (ATP) were produced when1 mol NADH was oxidized through the respiratory chain of this microorganism. The true growth yield for ATP (Y_ATP) and specific ATP consumption rate for maintenance (Q) calculated with this value were 0.0106 g dry cell/mmol ATP and 5.2 mmol ATP/g dry cell/hr, respectively. Using the relationships between specific growth rate (μ) and (Q) and between μ and Q_G obtained from chemostat-culture data, cell and glucose concentration histories were estimated from the carbon dioxide production rate during the batch culture. The estimated cell concentrations agreed with the experimentally measured values. Glucose concentration were slightly overestimated.     

The response by microorganisms to steady state growth in controlled concentrations of oxygen and glucose. I. Candida utilis

Dissolved oxygen and glucose concentrations have been independently maintained at various concentrations for extended periods during growth of Candida utilis in continuous culture. Simultaneous observations of cytochrome concentration, growth rate, rates of uptake of oxygen and glucose and rates of production of CO₂, ethanol and acid have been made during steady states at various levels of oxygen and glucose. There is an inverse relationship between dissolved oxygen and cytochrome and between glucose cocentration and cytochrome. Studies of the transient state following a step change from high to low dissolved oxygen show that there is a lag of about 10 hr during which there is no change in the above parameters. This is followed by rapid oscillatory changes in cytochrome content and a change to a more fermentative metabolism.     

Use of the glucose oxidase system to measure oxygen transfer rates

This investigation used the glucose oxidase system to simulate oxygen transfer rate in fermentation broths. It was demonstrated that the fungal preparation contained sufficient lactonase activity so that D -glucono-δ-lactone did not accumulate and that the rate of production of gluconic acid was proportional to the oxygen uptake rate. Enzyme concentrations of 1.5–2 g/1 were found adequate to determine oxygen absorption rates in shake flasks while maintaining the dissolved oxygen concentration of low levels. The apparent Michaelis constant for oxygen, K_m(O₂), was found to be 27% saturation with air; this value along with experimentally determined uptake rates could be used to calculate dissolved oxygen concentration in lieu of using a dissolved oxygen probe. Enzyme concentrations of 5 g/l were sufficient to give linear acid production and low dissolved oxygen concentrations in a bench-scale fermenter with no foaming or enzyme deactivation. The method is considered more valid and easier to employ than previously utilized techniques such as sulfite oxidation. Extension of the system to evaluating aeration effectiveness and scaleup of fermentation equipment is discussed.     

Influence of long-term hypoxia on the energy metabolism of the haemoglobin-containing bivalve Scapharca inaequivalvis: critical O2 levels for metabolic depression

Summary The oxygen consumption rate of Scapharca inaequivalvis measured under normoxic conditions over 48 h showed a significant daily cycle with lowest values occurring shortly after the dark period; all hypoxia exposure experiments were carried out during the declining part of the cycle. Animals were exposed to a constant level of hypoxia for a 12-h period in a series of 14 experiments, each at a different oxygen tension. The oxygen consumption was measured continuously, and the extent of accumulation of end-products (succinate and propionate), and the inhibitory effect of adenosine triphosphate on phosphofructokinase were determined at the end of exposures. All three parameters (oxygen consumption, end-product accumulation, phosphofructokinase inhibition) showed a remarkable correlation with major changes occurring between 2.5 and 1.5 ppm (7 and 4 kPa) O₂. The oxygen consumption rates showed a drop to 6% of the normoxic rate, but a consistent low consumption remained below 2 ppm (5.5 kPa) which partly recovered over the 12-h exposure period by about three-fold. Succinate and propionate accumulated progressively between 2.5 and 1.5 ppm (7 and 4 kPa); at [O₂]<1.5 ppm (4kPa) the concentration did not increase further, indicating that anaerobic metabolism had reached a maximum. Over the same range, phosphofructokinase showed an increased sensitivity for adenosine triphosphate, the lower inhibitor concentration at 50% V _max value pointing to depression of glycolytic rate. Despite the activation of anaerobic metabolism and the evident depression of aerobic metabolism, simple calculation demonstrates that Scapharca inaequivalvis relies mainly on aerobic metabolism even during severe hypoxia. It is assumed that the occurrence of haemoglobin in this species is essential for its capacity to survive long periods of hypoxia.Abbreviations ATP adenosine triphosphate - I₅₀ inhibitor concentration at 50% V _max - PFK phosphofructokinase - P _c critical PO₂ - SEM standard error of mean - VO₂ oxygen consumption rate - ww wet weight     

Study of the non-photochemical dark rise in chlorophyll fluorescence in pre-illuminated leaves of various C3 and C4 plants submitted to partial anaerobiosis

Changes in chlorophyll fluorescence yield were studied during a dark period in pre-illuminated leaves of various C3 and C4 plants. The oxygen content in the gaseous atmosphere was either normal (21 kPa) or low (1.5 or 0.36 kPa). C3 and C4 plants of the NAD malic enzyme subgroup showed an initial rise in fluorescence at the onset of the dark period with an amplitude depending on the O₂ level in the gas. In C4 plants belonging to the other two subgroups, the slow rise was absent or of very low size. At high [O₂], the fluorescence level decreased in some minutes to the initial F₀ level (determined in dark-adapted leaves). Conversely at low [O₂], the fluorescence yield remained higher than F₀ in all the C4 plants studied, whereas it decreased slowly to the F₀ level in the different C3 plants. At low [O₂], the fluorescence level decreased rapidly to F₀ when introducing for 30 s, a high O₂ level or when giving a 15-s far-red illumination. At the end of these treatments, the fluorescence level re-increased. These results demonstrate the presence at low [O₂] of highly fluorescent ‘closed' photosystem II centres containing Q^-_A in equilibrium with reduced plastoquinone molecules of the chloroplastic pool. Reoxidation of the plastoquinone pool would be dependent on the functioning of an oxidase probably dependent on a chlororespiration process fully active at O₂ levels higher than 2 kPa. The source of reducing equivalents for the plastoquinone pool is discussed.     

Stromal Phosphate Concentration Is Low during Feedback Limited Photosynthesis

It has been hypothesized that photosynthesis can be feedback limited when the phosphate concentration cannot be both low enough to allow starch and sucrose synthesis at the required rate and high enough for ATP synthesis at the required rate. We have measured the concentration of phosphate in the stroma and cytosol of leaves held under feedback conditions. We used non-aqueous fractionation techniques with freeze-clamped leaves of Phaseolus vulgaris plants grown on reduced phosphate nutrition. Feedback was induced by holding leaves in low O₂ or high CO₂ partial pressure. We found 7 millimolar phosphate in the stroma of leaves in normal oxygen but just 2.7 millimolar phosphate in leaves held in low oxygen. Because 1 to 2 millimolar phosphate in the stroma may be metabolically inactive, we estimate that in low oxygen, the metabolically active pool of phosphate is between negligible and 1.7 millimolar. We conclude that halfway between these extremes, 0.85 millimolar is a good estimate of the phosphate concentration in the stroma of feedback-limited leaves and that the true concentration could be even lower. The stromal phosphate concentration was also low when leaves were held in high CO₂, which also induces feedback-limited photosynthesis, indicating that the effect is related to feedback limitation, not to low oxygen per se. We conclude that the concentration of phosphate in the stroma is usually in excess and that it is sequestered to regulate photosynthesis, especially starch synthesis. The capacity for this regulation is limited by the coupling factor requirement for phosphate.     

Observer design for differential-algebraic model of an aerobic culture of a recombinant yeast

The mathematical model of an aerobic culture of recombinant yeast presented in work by Zhang et al. (1997) is given by a differential-algebraic system. The classical nonlinear observer algorithms are generally based on ordinary differential equations. In this paper, first we extend the nonlinear observer synthesis to differential-algebraic dynamical systems. Next, we apply this observer theory to the mathematical model proposed in Zhang et al. (1997). More precisely, based on the total cell concentration and the recombinant protein concentration, the observer gives the online estimation of the glucose, the ethanol, the plasmid-bearing cell concentration and a parameter that represents the probability of plasmid loss of plasmid-bearing cells. Numerical simulations are given to show the good performances of the designed observer.Symbols C ₁ activity of pacing enzyme pool for glucose fermentation (dimensionless) - C ₂ activity of pacing enzyme pool for glucose oxidation (dimensionless) - C ₃ activity of pacing enzyme pool for ethanol oxidation (dimensionless) - E ethanol concentration (g/l) - G glucose concentration (g/l) - k _a regulation constant for (g glucose/g cell h^–1) - k _b regulation constant for (dimensionless) - k _c regulation constant for (g glucose/g cell h^–1) - k _d regulation constant for (dimensionless) - K _m1 saturation constant for glucose fermentation (g/l) - K _m2 saturation constant for glucose oxidation (g/l) - K _m3 saturation constant for ethanol oxidation (g/l) - L ( t) time lag function (dimensionless) - p probability of plasmid loss of plasmid-bearing cells (dimensionless) - P recombinant protein concentration (mg/g cell) - q _G total glucose flux culture time (g glucose/g cell h) - t culture time (h) - t _lag lag time (h) - X total cell concentration (g/l) - X ⁺ plasmid-bearing cell concentration (g/l) - Y ^F _{X / G} cell yield for glucose fermentation pathway (g cell/g glucose) - Y ^O _{X / G} cell yield for glucose oxidation pathway (g cell/g glucose) - Y _{X / E} cell yield for ethanol oxidation pathway (g cell/g ethanol) - Y _{E / X} ethanol yield for fermentation pathway based on cell mass (g ethanol·g cell) - ₂ glucoamylase yield for glucose oxidation (units/g cell) - ₃ glucoamylase yield for ethanol oxidation (units/g cell) - µ₁ specific growth rate for glucose fermentation (h^–1) - µ₂ specific growth rate for glucose oxidation (h^–1) - µ₃ specific growth rate for ethanol oxidation (h^–1) - µ_1max maximum specific growth rate for glucose fermentation (h^–1) - µ_2max maximum specific growth rate for glucose oxidation (h^–1) - µ_3max maximum specific growth rate for ethanol oxidation (h^–1)     

Performance assessment of two patent strains ofZymomonas mobilis in batch and continuous fermentations

Summary The performance ofZymomonas mobilis strains ATCC 31821 and ATCC 31823 was assessed in batch and continuous culture. In batch culture using a medium containing 250 g/l glucose, identical maximum specific growth rates of 0.16/h were found, though final biomass concentration and growth yield were significantly lower for ATCC 31 823 than for ATCC 31 821. Final ethanol concentrations in this medium were about 110 g/l vor both organisms. In continuous culture at increasing dilution rates using a medium containing 100 g/l glucose, no significant differences were seen between the two strains with respect to the fermentation parameters studied. For ATCC 31 821, maximum rates of glucose uptake (Q_s) and ethanol produktion (Q_p) of 8.7 g glu/g/h and 4.4 g eth/g/h, respectively, were found. Both strains showed a similar performance at a fixed dilution rate of 0.1/h, where maximum ethanol concentrations of about 68 g/l were reached at a feed glucose concentration of about 139 g/l. At this dilution rate the maximum values of Q_s and Q_p were about 5.8 g glu/g/h and 2.8 g eth/g/h, respectively. Test tube experiments showed that growth, measured as optical density, decreased with increasing concentrations of exogenous ethanol with complete inhibition of growth at ethanol concentrations >8% (v/v). As evidenced by the results presented here, we have been unable to practice the invention as described in U.S. Patent 4,403,034 (Rogers and Tribe 1983).Nomenclature D Dilution rate, 1/h - _max maximum specific growth rate, 1/h - S_R Initial substrate concentration, g glucose/1 - S Residual substrate concentration, g glucose/1 - S₀ Effluent substrate concentration, g glucose/1 - X Blomass concentration; g cells/l - OD₆₂₀ Optical density at 620 nm, dimensionless - [P] Product concentration, g ethanol/1 - Y_x/s Growth yield, g cells/g glucose used - Y_p/s Product yield, g ethanol/g glucose used - %, Yield Percentage yield, Y_p/sx100/Y _p ^s/max =Y_p/sx100/0.51 - Q_s Specific rate of glucose uptake, g glucose/g cells/h - Q_p Specific rate of ethanol formation, g ethanol/g cells/h - m_e Maintenance energy coefficient, g glucose/g cells/h - VP Volumetric productivity, g ethanol/l/h - t Fermentation time, h     

Regulatory aspects of bakers' yeast metabolism in aerobic fed-batch cultures

A highly instrumented computer-coupled bioreactor is used to investigate metabolic changes of Saccharomyces cerevisiae in aerobic fed-batch systems which are generally applied in bankers' yeast manufacture. The four types of metabolism (oxidation of glucose, aerobic fermentation, oxidation of glucose and ethanol, and oxidation of ethanol) appearing in such systems are characterized by four significant fermentation parameters: Respiratory quotient (RQ), glucose uptake rate (Q_g), ethanol turnover rate (Q_EtOH), and growth yield on glucose (Y_g). Below the critical glucose concentration glucose and ethanol are utilized simultaneously. The shift from aerobic fermentation to nondiauxic growth on glucose and ethanol is not only dependent on glucose concentration. but also on the precultivation on cells. The uptake of ethanol is controlled by the glucose supply except in the case when ethanol is limiting; the oxygen uptake rate (Q_o2), however, is unaffected by the ratio of Q_g and Q_EtOH. Critical glucose concentration is not a constant value for a particular strain, but varies corresponding to the nutritional state of the cells.     

Chemostat studies on the assimilation of hexadecane by the yeastCandida tropicalis

Summary The yeastCandida tropicalis was grown in a chemostat with hexadecane as the sole carbon source. The influence of the dilution rate, oxygen and ammonium limitation on s, x, Y_s, Q_{O 2}, Q_{CO 2}, and Q_s was investigated. When the extracellular hexadecane concentration exceeded 120 mg l^–1 (at dilution rates close to D_c, at pO₂ below 2.54 kPa and at ammonium limited growth) Y_s decreased and Q_{O 2}, Q_{CO 2}, and Q_s increased. It was concluded that uncoupling of the mitochondrial respiratory chain occurred under these conditions. The Q_{O 2} was determined by two different methods: first in situ, with a gasanalyzer directly connected to the bioreactor to analyze the outcoming gas, and second, with a sample from the bioreactor transferred to a Clark-type oxygen electrode. When cell growth was not oxygen limited in the chemostat (pO₂ above 2.54 kPa), no apparent difference between the in situ and the dynamically determined Q_{O 2} was observed. In contrast, when cell growth was oxygen limited in the chemostat, the Q_{O 2} measured in the Clark-type oxygen electrode was remarkably higher than the in situ Q_{O 2}. This indicates that the electron transport chains are limited bythe oxidases, when the cells lack oxygen.     

Invertase and phosphatase of yeast in a phosphate-limited continuous culture

Summary Deficiency of inorganic phosphate caused the hyper production of invertase and the derepression of acid phosphatase in a continuous culture ofSaccharomyces carlsbergensis. The specific invertase activity was 40,000 enzyme units per g dry cell weight at a dilution rate lower than 0.05 h^–1 with a synthetic glucose medium of which the molecular ratio of KH₂PO₄ to glucose was less than 0.006. This activity is eight fold higher than in a batch growth and 1.5 fold as much as the highest enzyme activity observed so far in a glucose-limited continuous culture.For the hyper production of invertase, it is necessary to culture the yeast continuously by keeping the Nyholm's conservative inorganic phosphate concentration at less than 0.2 m mole per g dry weight cell. The derepression of acid phosphatase brought about by phosphate deficiency, was similar in both batch and continuous cultures.Nomenclature D dilution rate of continuous culture (h^–1) - E_i invertase concentration in culture (enzyme unit l^–1) - E_p acid phosphatase concentration in culture (enzyme unit l^–1) - P inorganic phosphate concentration in culture (mM) - S glucose concentration in culture (mM) - X cell concentration in culture (g dry weight cell l^–1) Greek Letter specific rate of growth (h^–1) Suffix f feed - 0 initial value     

Effects of frost hardening, dehardening and freezing stress on in vivo chlorophyll fluorescence of seedlings of Scots pine (Pinus sylvestris L.)

Abstract. The kinetics of in vivo chlorophyll fluorescence of photosystem II (PS II) was measured at room temperature and 77 K during frost hardening of seedlings of Scots pine (Pinus sylvestris L.), and after exposure of frost-hardened shoots to sub-freezing temperatures. A more pronounced decrease in variable fluorescence yield for the upper exposed than for the lower shaded surface of the needles suggested that some photoinhibition occurred during prolonged frost hardening at 50 μmol photons m^?2 s^?1 and 4°C. Reversible inhibition of photosynthesis after exposure to sub-freezing temperatures was initially manifested as an increase of steady-state energy-dependent fluorescence quenching (q_E) and a reduction in the rate of O₂ evolution. Further inhibition after treatment at still lower temperatures caused a progressive decline of steady-state photochemical quenching (q_Q) and the rate of O₂ evolution, whereas q_E remained high. This implies an inactivation of enzymes in the photosynthetic carbon reduction cycle decreasing the consumption of ATP and NADPH, which is likely to cause an increase of membrane energization and a reduction of the primary electron acceptor (Q_A) of PS II. Alternatively, the changes in q_Q and q_E might be attributed to an inhibition of photophosphorylation. Severe, irreversible damage to photosynthesis resulted in a suppression of q_E and of variable fluorescence yield, probably because the photochemical efficiency of PS II was impaired. Changes in the fast fluorescence kinetics at room temperature after severe freezing damage were interpreted as an inhibition of the electron flow from Q_A to the plastoquinone pool. It is suggested that irreversible freezing injury to needles of frost-hardened P. sylvestris causes damage to the Q_B,-protein.     

The effect of Eh on regulatory processes in facultative anaerobes

On increasing aeration rate in chemostat cultures of E. coli the redox potential (E_h) of the culture changes from ?l50 mv to +250 mv. During this period only a slight increase in measured dissolved oxygen concentration is observed. It is suggested that E_h be used as a control variable for aeration in the oxygen limited growth condition, whilst dissolved oxygen concentration be used as control variable in the presence of excess oxygen. Change in cytochrome b₁, three tricarboxylic acid cycle enzymes and hydrogenase can be related to culture E_h. These changes are discussed.     

Induction by glucose of an antimycin-insensitive,azide-sensitive respiration in the yeast Kluyveromyces lactis

Increasing the glucose concentration from 0.1 to 10% in exponentially growing cultures of Kluyveromyces lactis CBS 2359 does not repress the antimycin-sensitive respiration (Q_{O 2} of 80 l O₂·h^-1·mg^-1 dry weight) but raises the antimycin-insensitive respiration from 3 to 12 l O₂·h^-1·mg^-1 dry weight. Antimycin A inhibits the growth of K. lactis on a variety of substrates with the exception of glucose at concentrations equal to or higher than 1% where substantial antimycin-insensitive respiratory rates are induced. It can be concluded that a minimal antimycin-insensitive Q_{O 2} is necessary for cellular growth when the normal respiratory pathway is not functional.The antimycin-insensitive respiration elicited by growth in high glucose concentrations is poorly inhibited by hydroxamate and is inhibited by 50% by 90 m azide or 1mm cyanide. These concentrations are much higher than those necessary to inhibit cytochrome c oxidase which is not involved in the antimycin-insensitive respiration as was demonstrated by spectral measurements. A pigment absorbing at 555 nm is specifically reduced after addition of glucose to antimycin-inhibited cells. The same pigment is reoxidized by further addition of high concentrations of sodium azide indicating its participation in the antimycin-insensitive, azide-sensitive respiration.     

The relationship between steady-state gas exchange of bean leaves and the levels of carbon-reduction-cycle intermediates

The relationship between the gas-exchange characteristics of attached leaves of Phaseolus vulgaris L. and the pool sizes of several carbon-reduction-cycle intermediates was examined. After determining the rate of CO₂ assimilation at known intercellular CO₂ pressure, O₂ pressure and light, the leaf was rapidly killed (<0.1 s) and the levels of ribulose-1,5-bisphosphate (RuBP), 3-phosphoglyceric acid (PGA), fructose-1,6-bisphosphate, fructose-6-phosphate, glucose-6-phosphate, glyceraldehyde-3-phosphate, and dihydroxyacetone phosphate were measured. In 210 mbar O₂, photosynthesis appeared RuBP-saturated at low CO₂ pressure and RuBP-limited at high CO₂ pressure. In 21 mbar (2%) O₂, the level of RuBP always appeared saturating. Very high levels of PGA and other phosphate-containing compounds were found with some conditions, especially under low oxygen.Abbreviations and symbols C₁ intercellular CO₂ pressure - PGA 3-phosphoglyceric acid - RuBP ribulose-1,5-bisphosphate - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase     

Control of continuous fed-batch fermentation process using neural network based model predictive controller

Cell growth and metabolite production greatly depend on the feeding of the nutrients in fed-batch fermentations. A strategy for controlling the glucose feed rate in fed-batch baker’s yeast fermentation and a novel controller was studied. The difference between the specific carbon dioxide evolution rate and oxygen uptake rate (Q _c − Q _o) was used as controller variable. The controller evaluated was neural network based model predictive controller and optimizer. The performance of the controller was evaluated by the set point tracking. Results showed good performance of the controller.     

Peroxidase activity of cytochrome <Emphasis Type="Italic">bd</Emphasis> from <Emphasis Type="Italic">Escherichia coli</Emphasis>

Cytochrome bd from Escherichia coli is able to oxidize such substrates as guaiacol, ferrocene, benzohydroquinone, and potassium ferrocyanide through the peroxidase mechanism, while none of these donors is oxidized in the oxidase reaction (i.e. in the reaction that involves molecular oxygen as the electron acceptor). Peroxidation of guaiacol has been studied in detail. The dependence of the rate of the reaction on the concentration of the enzyme and substrates as well as the effect of various inhibitors of the oxidase reaction on the peroxidase activity have been tested. The dependence of the guaiacol-peroxidase activity on the H₂O₂ concentration is linear up to the concentration of 8 mM. At higher concentrations of H₂O₂, inactivation of the enzyme is observed. Guaiacol markedly protects the enzyme from inactivation induced by peroxide. The peroxidase activity of cytochrome bd increases with increasing guaiacol concentration, reaching saturation in the range from 0.5 to 2.5 mM, but then starts falling. Such inhibitors of the ubiquinol-oxidase activity of cytochrome bd as cyanide, pentachlorophenol, and 2-n-heptyl 4-hydroxyquinoline-N-oxide also suppress its guaiacol-peroxidase activity; in contrast, zinc ions have no influence on the enzyme-catalyzed peroxidation of guaiacol. These data suggest that guaiacol interacts with the enzyme in the center of ubiquinol binding and donates electrons into the di-heme center of oxygen reduction via heme b ₅₅₈, and H₂O₂ is reduced by heme d. Although the peroxidase activity of cytochrome bd from E. coli is low compared to peroxidases, it might be of physiological significance for the bacterium itself and plays a pathophysiological role for humans and animals.