Enhanced oxygen transfer rates in fermentation using soybean oil-in-water dispersions

Summary The effect of soybean oil on the volumetric oxygen transfer coefficient during the cultivation ofAerobacter aerogenes cells is presented. For our aeration-agitation conditions (0.278 vvm and 500 rpm), it has been demonstrated that the use 19% (v/v) of soybean oil enabled a 1.85-fold increase of thek _l a coefficient (calculated on a per liter aqueous phase basis). For smaller volumetric oil fractions,k _L a increased linearly with the oil loading. Because of the oxygen-vector properties of soybean oil, this oil is able to significantly increase thek _L a of a bioreactor.Nomenclature C^*, C saturation and actual dissolved oxygen concentrations respectively (g/m³) - K_La volumetric oxygen transfer coefficient (h^–1) - K_La_initial k _La measured before the oil addition (h^–1) - M_O2 molar mass of oxygen (dalton) - N oxygen transfer rate (g/m³. h) - P_O2. P_N2 partial pressures ofO ₂ andN ₂ in the gas (atm) - P_H2OT partial pressure of water in air at the temperatureT (atm) - P_T total pressure (atm) - Q₀ volumetric flow rate of outlet air before seeding (m³/h) - Sp spreading coefficient (dynes/cm) - T absolute temperature of outlet gas (K) - V_i volume of the liquidi in the fermentor (m³) - V_M molar volume at 273 K and 1 atm (m³/mole) - _ij interfacial tension betweeni andj componants (dynes/cm) - _v volumetric fraction of the oil (v/v) - G gas - O oil - W water - i inlet - o outlet     

A graphical method of determining the Michaelis-Menten constant free of external mass transfer resistance for immobilized enzymes in a packed bed reactor

Summary A graphical method of determining the Michaelis-Menten constant free of the external mass transfer resistance for a packed bed immobilized enzyme system was illustrated with examples from 3 different enzyme reactions. The intercept at the ordinate obtained by the straight line extrapolation of data points in the plot of apparent K_m value vs. the reciprocal of superficial velocity in column allowed an easy calculation of K_m free of external mass transfer resistance. An asymptotic value of apparent K_m value at infinite zero superficial velocity was ascribed to the fact that the mass transfer coefficient k_L, approached a definite value at this condition.Nomenclature K_m Michaelis-Menten constant, M/L³ - K_m' K_m free of external mass transfer resistance in a given ionic strength, M/L³ - Km" apparent K_m with external mass transfer resistance, M/L³ - S substrate concentration, M/L³ - S_o initial substrate concentration, M/L³ - k₂ rate constant, t^-1 - E enzyme concentration in support, M/L³ - void volume per unit volume of reactor, dimensionless - u superficial velocity of substrate, L/t - K_L mass transfer coefficient in liquid film, L/t - a external surface area of support per unit volume of reactor, L^-1 - ratio of average channeling length to particle diameter, dimensionless - d_p diameter of support particle, L - X fractional conversion of substrate, dimensionless - H partition coefficient, dimensionless - k a constant, 3 k₂E(1-)d_p/4 - T space time, t - N molecular flux, M/L²t - r radius of immobilized enzyme particle, L     

Microcalorimetric investigations of the metabolism of yeasts. growth in batch and chemostat cultures on ethanol medium

Summary In the presence of protein, Hansenula polymorpha cultivation medium exhibits a maximum volumetric mass transfer coefficient, k_La, as function of the employed antifoam agents (soy oil and Desmophen 3600). With diminishing superficial gas velocity this maximum disappeas.Symbols E_G Relative gas holdup - k_La Volumetric mass transfer coefficient (s^–1) - w_SL Superficial liquid velocity (cm s^–1) - w_SG Superficial gas velocity (cm s^–1)     

Kinetics of Transport and Phosphorylation of 2-Fluoro-2-Deoxy-d-Glucose in Rat Brain

Abstract: The kinetics of transport across the blood-brain barrier and metabolism in brain (hemisphere) of [¹⁴C]2-fluoro-2-deoxy-d -glucose (FDG) were compared to that of [³H]2-deoxy-d -glucose (DG) and d -glucose in the pentobarbital-anesthetized adult rat. Saturation kinetics of transport were measured with the brain uptake index (BUI) method. The BUI for FDG was 54.3 ± 5.6. Nonlinear regression analysis gave a K_m of 6.9 ± 1.1 mM and a V_max of 1.70 ± 0.32 μmol/min/g. The K₁ for glucose inhibition of FDG transport was 10.7 ± 4.4 mM. The kinetic constants of influx (k₁) and efflux (K₂) for FDG were calculated from the K_m, V_max, and glucose concentrations of the hemisphere and plasma (2.3 ± 0.2 μmol/g and 9.9 ± 0.4 mM, respectively). The transport coefficient (k_{1 FDG}/k₁glucose) was 1.67 ± 0.07 and the phosphorylation constant was 0.55 ± 0.16. The predicted lumped constant for FDG was 0.89, whereas the measured hexose utilization index for FDG was 0.85 ± 0.16. Conclusion: The value for the lumped constant can be predicted on the basis of the known kinetic constants of FDG and glucose transport and metabolism, as well as brain and plasma glucose levels. Knowledge of the lumped constant is crucial in interpreting data obtained from ¹⁸FDG analysis of regional glucose utilization in human brain in pathological states. We propose that the lumped constant will rise to a maximum equal to the transport coefficient for FDG under conditions of transport limitation (hypoglycemia) or elevated glycolysis (ischemia, seizures), and will fall to a minimum equal to the phosphorylation coefficient during phosphorylation limitation (extreme hyperglycemia).     

Model for the production of L-tryptophan from L-serine and indole by immobilized cells in a three-phase liquid-impelled loop reactor

Production of L-tryptophan from L-serine and indole catalyzed by Escherichia coli, immobilized in k-carrageenan gel beads, is technically feasible in the liquidimpelled loop reactor (LLR), using an organic solvent, e.g. n-dodecane.With L-serine in large excess intrinsic reaction kinetics is approximately first order with respect to indole, with a reaction constant of 8.5×10^–5 m³ kg _dw ^–1 s^–1.The overall process kinetics is jointly controlled by intrinsic kinetics and by intraparticle mass transfer resistance, which can be quantified using an effectiveness factor.Mass transfer of indole from the organic to the aqueous phase and from the aqueous to the gel phase are relatively fast and thus have negligible influence in the overall process kinetics, under the operational conditions tested. However, they may become important if the process is intensified by increasing the cell concentration in the gel and/or the gel hold-up in the reactor.A simple model which includes indole mass balances over the aqueous and organic phases, mass transfer and reaction kinetics, with parameters experimentally determined in independent experiments, was successful in simulating L-tryptophan production in the LLR.List of Symbols a, b, c coefficients of the equilibrium curve for indole between organic and aqueous phases - A, B, C, D, E, F auxiliary variables used in liquid-liquid mass transfer studies - a _x specific interfacial area referred to the volume of the aqueous phase (m^–1) - A _x interfacial area (m²) - a _Y specific interfacial area referred to the volume of the organic phase (m^–1) - A _Y interfacial area (m²) - C _b substrate concentration in the bulk of the aqueous phase (kg m^–3) - C _e substrate concentration in exit stream (kg m^–3) - C _E biocatalyst concentration referred to the aqueous phase (kg m^–3) - C _{E s} biocatalyst concentration referred to the volume of gel (kg m^–3) - C _s substrate concentration at the gel surface (kgm^–3) - d, e, f coefficients of the equilibrium curve for indole between aqueous and organic phases - dp particle diameter (m) - K ₂ kinetic constant (s^–1) - K ₁ kinetic constant K₂/K_M (kg^–1 m³ s^–1) - K _M Michaälis-Menten constant (kgm^–3) - K _X mass transfer coefficient referred to the aqueous phase (ms^–1) - K _Xa_X volumetric mass transfer coefficient based on the volume of the aqueous phase (s^–1) - k _Y mass transfer coefficient referred to the organic phase (ms^–1) - K _Ya_Y volumetric mass transfer coefficient based on the volume of the organic phase (s^–1) - N _X mass flux of indole from organic to aqueous Phase (kg m^–2s^–1) - N _Y mass flux of indole from aqueous to organic phase (kg m^–2s^–1) - Q _e volumetric flow rate in exit stream (m³s^–1) - Q _f volumetric flow rate in feed stream (m³s^–1) - _obs observed reaction rate (kg s^–1 m^–3) - intrinsic reaction rate (kg s^–1 m^–3) - Re Reynolds number - Sc Schmidt number - Sh Sherwood number - t time (s) - u superficial velocity (m s^–1) - V _max maximum reaction rate (kg s^–1m^–3) - V _S volume of the support (m³) - V _X volume of aqueous phase (m³) - V _Y volume of the organic phase (m³) - X indole concentration in the aqueous phase (kgm^–3) - Y indole concentration in the organic phase (kg m^–3 Greek Letters overall effectiveness factor - _e external effectiveness factor - _i internal effectiveness factor - Thiele module A fellowship awarded to one of us (D.M.R.)by INICT is gratefuly acknowledged.     

Liquid-phase mass transfer in fixed-bed of polyurethane foam matrices containing immobilized anaerobic sludge

This paper reports on the results of liquid-phase mass transfer experiments carried-out in a bed of immobilized anaerobic sludge. The liquid superficial velocity (v_s) was found to deeply affect the liquid-phase volumetric mass transfer coefficient (k_sa) in the v_s range of 0.007 to 0.075 cm.s^–1. Moreover, k_sa increased exponentially with v_s in that range, due to the decrease of the external mass transfer resistance.     

Modelling the uptake of nitrate by a growing plant with an adjustable root nitrate uptake capacity

A new model is presented to predict the plant uptake of nitrate supplied by diffusion and mass flow to its roots. Plant growth, root-shoot ratio and the plant's nitrate uptake capacity are all set dependent on the plant's N nutrition state. By thoroughly integrating processes occurring in both plant and soil, the model enables to control the relative importance of both under a wide range of different nutritional scenarios.Soil parameters D₀ diffusion coefficient in water (m² day^-1) - D_e diffusion coefficient in soil (m² day^-1) - C nitrate concentration in soil (mol m^-3) - f tortuosity (-) - volumetric moisture content (-) - R radial distance from root axis (m) Plant parameters b₁, b₂ parameters of biomass partitioning Equation (10) - IR interroot distance (m) - K_mU Michaelis-Menten constant of the uptake system (mol m^-3) - K_mNRA Michaelis-Menten constant of nitrogen reduction system (mol g^-1) - k₁, k₂, k₃ parameters of growth model Equation (9) - L_v Root length density (m m^-3) - NO_{3 set} ^- Set point of the cytoplasmatic nitrate pool (mol g^-1 dw) - NO_{3 c} ^- cytoplasmatic nitrate concentration (mol g^-1 dw) - NO_{3 v} ^- vacuolar nitrate concentration (mol g^-1 dw) - NRA_max maximum nitrate reductase activity (mol g^-1 dw day^-1) - N_re reduced nitrogen content (mol) - N_remax maximum reduced N concentration in the plant (mol g^-1 dw) - P partitioning coefficient of nitrate between cyplasm and vacuole - R(1) root radius (m) - RGR relative growth rate (day^-1) - U uptake rate (mol day^-1 m^-2) - U_max maximum uptake rate (Eq. 6) (day^-1 m^-2) - Vo water flux at root surface (m day^-1) - W_r root dry weight (g) - W_sh shoot dry weight (g) - X model parameter: number of root compartments - Y model parameter: number of nodes     

Kinetic analysis of lactate dehydrogenase in situ in mouse liver determined with a quantitative histochemical technique

Summary The kinetics of lactate dehydrogenase in situ were studied in sections of unfixed liver of the male mouse using a quantitative histochemical technique. The sections were incubated on substrate-containing gel films. The absorbance of the final reaction products deposited in a single hepatocyte was measured continuously during the incubation as a function of incubation time using a scanning microdensitometer. The absorbance increased non-linearly during the first minute of incubation, but linearly for at least the next 3 min afterwards. The initial velocity (v _i ) of the dehydrogenase was calculated from two equations proposed previously by us, v _i=2.82 °A and v _i =v+2°A, where v and °A are, respectively, the gradient and intercept o linear regression line of absorbance on time for incubation times between 1 and 3 min.The dependence of v _i on lactate concentration gave the following mean kinetic constants. For periportal hepatocytes, the apparent K _m =14 mM and V _max =80 moles hydrogen equivalents formed cm^–3 hepatocyte cytoplasm min^–1. For pericentral hepatocytes, K _m =12 mM and V _max =87 moles hydrogen equivalents cm^–3 min^–1. The K _m values are very similar to those determined previously from biochemical assays. The concentrations of the enzyme in single hepatocytes calculated from the V _max values are in good agreement with those obtained by another method. These data substantiate the validity of our equations.     

Extraction of hemoglobin with calixarenes and biocatalysis in organic media of the complex with pseudoactivity of peroxidase

The present work involves the use of p-tert-butylcalix[4,6,8]arene carboxylic acid derivatives (^tButyl[4,6,8]CH₂COOH) for selective extraction of hemoglobin. All three calixarenes extracted hemoglobin into the organic phase, exhibiting extraction parameters higher than 0.90. Evaluation of the solvent accessible positively charged amino acid side chains of hemoglobin (PDB entry 1XZ2) revealed that there are 8 arginine, 44 lysine and 30 histidine residues on the protein surface which may be involved in the interactions with the calixarene molecules. The hemoglobin–^tButyl[6]CH₂COOH complex had pseudoperoxidase activity which catalysed the oxidation of syringaldazine in the presence of hydrogen peroxide in organic medium containing chloroform. The effect of pH, protein and substrate concentrations on biocatalysis was investigated using the hemoglobin–^tButyl[6]CH₂COOH complex. This complex exhibited the highest specific activity of 9.92 × 10^?2 U mg protein^?1 at an initial pH of 7.5 in organic medium. Apparent kinetic parameters (V′_max, K′_m, k′_cat and k′_cat/K′_m) for the pseudoperoxidase activity were determined in organic media for different pH values from a Michaelis–Menten plot. Furthermore, the stability of the protein–calixarene complex was investigated for different initial pH values and half-life (t_1/2) values were obtained in the range of 1.96 and 2.64 days. Hemoglobin–calixarene complex present in organic medium was recovered in fresh aqueous solutions at alkaline pH, with a recovery of pseudoperoxidase activity of over 100%. These results strongly suggest that the use of calixarene derivatives is an alternative technique for protein extraction and solubilisation in organic media for biocatalysis.     

The effect of temperature,light-spectrum,desiccation and salinity gradients on the photosynthetic performance of a subtidal brown alga,Sargassum macrocarpum,from Japan

The effect of temperature, light-spectrum, desiccation and salinity gradients on the photosynthesis of a Japanese subtidal brown alga, Sargassum macrocarpum (Fucales), was determined using a pulse amplitude modulation-chlorophyll fluorometer and dissolved oxygen sensors. Temperature responses of the maximum (F_v/F_m in darkness) and effective (ΔF/F_m′ at 50 μmol photons m⁻² s⁻¹; = Φ_PSII) quantum yields during 6-day culture (4–36°C) remained high at 12–28°C, but decreased at higher temperatures. Nevertheless, ΔF/F_m′ also dropped at temperatures below 8°C, suggesting light sensitivity under chilling temperatures because F_v/F_m remained high. Photosynthesis–irradiance responses at 24°C under red (660 nm), green (525 nm), blue (450 nm) and white light (metal halide lamp) showed that maximum net photosynthesis under blue and white light was greater than under red and green light, indicating the sensitivity and photosynthetic availability of blue light in the subtidal light environment. In the desiccation experiment, samples under aerial exposure of up to 8 h under dim-light at 24°C and 50% humidity showed that ΔF/F_m′ quickly declined after more than 45 min of emersion; furthermore, ΔF/F_m′ also failed to recover to initial levels even after 1 day of rehydration in seawater. Under the emersion state, the ΔF/F_m′ remained high when the relative water content (RWC) was greater than 50%; in contrast, it quickly dropped when the RWC was less than 50%. When the RWC was reduced below 50%, ΔF/F_m′ did not return to initial levels, regardless of subsequent re-hydration, suggesting a low capacity of photosynthesis to recover from desiccation. The stenohaline response of photosynthesis under 3-day culture is evident, given that ΔF/F_m′ declined when salinity was beyond 20–40 psu. Adaptation to subtidal environments in temperate waters of Japan can be linked to these traits.     

Dual-substrate inhibition kinetic studies for recombinant human interferon gamma producing Pichia pastoris

Pichia pastoris is considered as one of the prominent host extensively used as a platform for heterologous protein production. In the present study, the growth inhibition kinetics of recombinant P. pastoris expressing human interferon gamma was studied under different initial substrate concentrations of gluconate (10–100?g?L^?1) and methanol (2–50?g?L^?1) in modified FM22 medium. The highest specific growth rate of 0.0206 and 0.019?hr^?1 was observed at 60?g?L^?1 of gluconate and 10?g?L^?1 of methanol, respectively. Various three- and four-parametric Monod-variant models were chosen to analyze the inhibition kinetics. The model parameters as well as goodness of fit were estimated using nonlinear regression analysis. The three-parameter Haldane model was found to be best fit for both gluconate (R²?=?0.95) and methanol substrate (R²?=?0.96). The parameter sensitivity analysis revealed that µ_max, K_i, and K_s are the most sensitive parameters for both methanol and gluconate. Different substrate inhibition models were fitted to the growth kinetic data and the additive form of double Webb model was found to be the best to explain the growth kinetics of recombinant P. pastoris.     

Catalyses by polymer complexes. VII. Enhanced esterolytic reactivity of polymer-coenzyme A,glutathione complexes

The association of coenzyme A(CoASH) and glutathione (GSH) with the water-soluble polymers and their esterolytic reactivities were evaluated through the reaction with p-nitrophenyl acetate in the presence of cationic polymer micelles: partially laurylated poly(2-ethyl-1-vinylimidazole) and poly(4-vinylpyridine). The polymer micelles with high lauryl-group content (more than 12 mol%) markedly accelerated the reaction at very low concentrations of the polymer. Other polymers with no or small lauryl-group content only slightly enhanced the association and the reaction rate. From the rate-polymer concentration profiles, the association constants (K) and the rate constants for thiol coenzymes bound to the polymer (k′_a,bound) were determined: for polymers with more than 12 mol % lauryl-group content, K_CoASH = 1110–2270 M^?1, K_GSH = 170–503M^?1, k′_a,bound at pH 8.65 = 142–341M^?1 sec^?1. k′_a,bound were 20–340 times larger than that observed in the absence of the polymer. The logarithm of k′_a,bound was found to be correlated well with the polymer hydrophobicity, indicating that the hydrophobic environment of the polymer activated the bound thiol anions. On the other hand, the polymer hydrophobicity did not correlate with the association constant.     

Sucrose inversion by immobilized yeast cells in a complete mixing reactor

Using whole cell invertase of Saccharomyces pastorianus, entrapped in spherical agar pellets, sucrose hydrolysis was carried out in a continuously fed fluidized bed reactor. The effective rate of reaction determined experimentally for the catalytic pellet was correlated with particle radius (R), intraparticle concentration of enzyme (E_p) and external concentration of substrate (S _R). The results were elucidated by theoretical analysis incorporating internal mass transfer resistance. At high degrees of diffusional resistance, the effectiveness factor was successfully estimted from Bischoff's equation. A dimensionless number, m_A ? R(k₂E_p/K_mD)^0.5(K_m/(K_m + S _R)), was used conveniently to predict the effectiveness factor in those cases wher the intraparticle diffusional effect was less significant. This number was employed to determine critical pellet size for an optimal reaction. The relationship between the properties of the pellet (size and intraparticle enzyme activity) and its apparent kinetic constants (k′₂ and K′_m), estimated according to Lineweaver-Burk, are discussed.     

Small scale vertical gradients of Arctic ice algal photophysiological properties

Photosynthetic parameters of phytoplankton and sea ice algae from landfast sea ice of the Chukchi Sea off Point Barrow, Alaska, were assessed in spring 2005 and winter through spring 2006 using Pulse Amplitude Modulated (PAM) fluorometry including estimates of maximum quantum efficiency (F _v/F _m), maximum relative electron transport rate (rETR_max), photosynthetic efficiency (α), and the photoadaptive index (E _k). The use of centrifuged brine samples allowed to document vertical gradients in ice algal acclimation with 5 cm vertical resolution for the first time. Bottom ice algae (0–5 cm from ice–water interface) expressed low F _v/F _m (0.331–0.426) and low α (0.098–0.130 (μmol photons m⁻²s⁻¹)⁻¹) in December. F _v/F _m and α increased in March and May (0.468–0.588 and 0.141–0.438 (μmol photons m⁻²s⁻¹)⁻¹, respectively) indicating increased photosynthetic activity. In addition, increases in rETR_max (3.3–16.4 a.u.) and E _k (20–88 μmol photons m⁻² s⁻¹) from December to May illustrates a higher potential for primary productivity as communities become better acclimated to under-ice light conditions. In conclusion, photosynthetic performance by ice algae (as assessed by PAM fluorometry) was tightly linked to sea ice salinity, temperature, and inorganic nutrient concentrations (mainly nitrogen).     

Oxygen transfer to slurries treated in a rotating drum operated at atmospheric pressure

The objective of this work was to determine (1) the effect of rotational speed (N) and lifters on the oxygen transfer coefficient (k _L) of a mineral solution and (2) the effect of solids concentration of a slurry soil-mineral solution on k _L, at a fixed value N (0.25 s⁻¹); in both cases the treatment was carried out in an aerated rotating drum reactor (RDR) operated at atmospheric pressure. First, the k _L for the mineral solution was in the range 6.38 × 10⁻⁴–7.69 × 10⁻⁴ m s⁻¹, which was of the same order of magnitude as those calculated for closed rotating drums supplied with air flow. In general, k _L of RDR implemented with lifters was superior or equal to that of RDR without lifters. For RDR implemented with lifters, k _L increased with N in the range 6.65 × 10⁻⁴–10.51 × 10⁻⁴ m s⁻¹, whereas k _L of RDR without lifters first increased with N up to N = 0.102 s⁻¹, and decreased beyond this point. Second, regarding soil slurry experiments, an abrupt fall of k _L (ca. 50%) at low values of the solid concentration (C _v) and an asymptotic pattern at high C _v were observed at N = 0.25 s⁻¹. These results suggest that mass transfer phenomena were commanded by the slurry properties and a semi-empirical equation of the form Sh = f(Re, Sc) seems to corroborate this finding.     

Bubble coalescence behaviour in biological media

Summary Volumetric mass transfer coefficients (k_La) were measured by a steady state method in a twin bubble column to characterize the coalescence behaviour of the medium. Employing Hansenula polymorpha cultivation broths, k_La values were compared with those measured in model media in the presence and absence of antifoam agents. The ratio of the volumetric mass transfer coefficient in the system investigated to that in water, , was employed to characterize the cultivation medium.Symbols a Specific gas/liquid interfacial area with regard to the liquid volume in reactor - d_e Dynamical equilibrium bubble diameter - d_H Perforated plate hole diameter - d_p Primary bubble diameter - d_S Sauter bubble diameter - F_v Liquid feed rate - H Bubbling layer height - k_L Gas/liquid mass transfer coefficient - k_La Volumetric mass transfer coefficient - m k_La/(k_La)_r coalescence index - m_corr Corrected coalescence index [Eq. (3)] - OTR Oxygen transfer rate - P_O Dissolved O₂-partial pressure in BS2 - P₁ Dissolved O₂-partial pressure in BS1 - P_O P_O/P_S relative oxygen saturation in BS2 - P₁ P₁/P_S relative oxygen saturation in BS1 - P_S Saturation dissolved oxygen partial pressure - R_c dn_B/dt coalescence rate - S Substrate concentration - t_F Time since the beginning of the cultivation - X Biomass concentration - V₁ Liquid volume in BS1 - w_SG Superficial gas velocity in BS1 - G Gas holdup in BS1 - ₁ V₁/F_v mean liquid residence time in BS1 - BS1 O₂ absorber column - BS2 O₂ desorber column - D Desmophen (antifoam agent) - NS Nutrient salt solution (Table 1)     

Pentobarbital Anesthesia Reduces Blood–Brain Glucose Transfer in the Rat

Abstract: Pentobarbital anesthesia (40 mg kg^–1) was accompanied by a 50% decrease of blood flow and a 40% decrease of unidirectional blood-brain glucose transfer in the parietal cortex of the rat brain. The correlation was explained by a decrease of the number of perfused capillaries. The maximal transport capacity, T_max, decreased from 409 to 235 μ mol 100 g^–1 min^–1 and the half-saturation constant, K_m, from 8.8 to 4.9 mm. At 8.3–8.7 mm -glucose in arterial plasma, the transfer constant (clearance) for unidirectional blood-brain transfer decreased from 0.195 ± 0.011 in awake rats to 0.132 ± 0.005 ml g^–1 min^–1 in anesthetized rats. Half of the decrease was due to less complete diffusion-limitation of glucose uptake at the low plasma flow rate in brain, the other half to the decreased T_max.     

CARRIER MEDIATED BLOOD-BRAIN BARRIER TRANSPORT OF CHOLINE AND CERTAIN CHOLINE ANALOGS

Blood-brain barrier (BBB) transport of choline and certain choline analogs was studied in adult and suckling rats, and additionally compared in the paleocortex and neocortex of adult rats. Saturable uptake was characterized by a single kinetic system in all cases examined, and in adult rat forebrains we determined a K_m= 442 ± 60 μM and V_max= 10.0 ± 0.6 nmol min^-1 g^-1. In 14–15-day-old suckling forebrains a similar K_m (= 404 ± 88 μM) but higher V_max (= 12.5 ± 1.5 nmol min^-1 g^-1) was determined. When choline uptake was compared in two regions of the forebrain, similar Michaelis-Menten constants were determined but a higher uptake velocity was found in the neocortex (i.e. neocortex K_m= 310 ± 103 μM and V_max= 12.6 ± 2.8 nmol min^-1g^-1; paleocortex K_m= 217 ± 76 μM and V_max= 7.2 ± 1.5 nmol min^-1 g^-1). Administration of radiolabelled choline at low (5 μM) and high (100 μM) concentrations, followed by microwave fixation 60 s later and chloroform-methanol-water separations of the homogenized brain did not suggest a relationship between concentration and the appearance of label in lipid or aqueous fractions as observed in another in-vitro study elaborating two-component kinetics of choline uptake. It was observed that 60s after carotid injection 12–14% of the radiolabel in the ipsilateral cortex was found in the chloroform-soluble fraction. Hemicholinium-3 (K_i= 111 μM), dimethylaminoethanol (K_i= 42 μM), tetraethyl ammonium chloride, tetramethyl ammonium chloride, 2-hydroxyethyl triethylammonium iodide, carnitine, normal rat serum, and to a lesser extent lithium and spermidine all inhibited choline uptake in the BBB. Unsubstituted ammonium chloride and imipramine did not inhibit choline uptake. No difference was observed in blood-brain barrier choline uptake of unanesthetised, carotid artery-catheterized animals, and comparable sodium pentobarbital-anesthetized controls.     

Blood–Brain Glucose Transport in the Conscious Rat: Comparison of the Intravenous and Intracarotid Injection Methods

Abstract: The unidirectional transfer of d -glucose from blood to parietal cortex tissue of the brain of awake rats was measured by single intravenous injection of tracer glucose, as well as by single intracarotid injection according to the method of Oldendorf. The maximal unidirectional blood–brain glucose transfer rate (T_max) was 407 μ mol (100 g)^–1 min^–1 when measured by intravenous injection, and 352 μ mol (100 g)^–1 min^–1 when measured by intracarotid injection. The half–saturation constants (K_m) were 7.8 mm and 16.8 HIM, respectively. The comparison shows that the two methods give similar results when cerebral perfusion is assessed accurately.     

Discrimination between rival laccase inhibition models from data sets with one inhibitor concentration using a penalized likelihood analysis and Akaike weights

Laccase from the white-rot fungus Fomes fomentarius was used for the biodegradation of ferulic acid (FA) in the presence of chloride anions. The initial reaction rates of substrate depletion were obtained by reverse-phase HPLC determination of remaining FA since substrate and reaction products have absorption peaks at similar wavelengths. Modelling of time-course data was accomplished by discrimination of the best enzyme inhibition equation from an initial set of seven different models based on Michaelis–Menten kinetics: competitive; uncompetitive; non-competitive; mixed; mixed hyperbolic; mixed parabolic; mixed hyperbolic and parabolic. Corrected Akaike information criterion was used to evaluate the relative merit of each kinetic model in order to rank them and find the more likely one. The discrimination results showed that the models with higher probabilities were the competitive and mixed inhibition types, but Akaike weights supported the selection of competitive inhibition (CI). After optimization by nonlinear regression, laccase kinetic parameters of FA biodegradation in the presence of chloride anions were: V_max?=?0.11?μmol?min^?1?mg^?1, K_m?=?44?μmol?L^?1 and a CI constant K_ic?=?14?mmol?L^?1.