Influence of Precision of Emission Characteristic Parameters on Model Prediction Error of VOCs/Formaldehyde from Dry Building Material

Mass transfer models are useful in predicting the emissions of volatile organic compounds (VOCs) and formaldehyde from building materials in indoor environments. They are also useful for human exposure evaluation and in sustainable building design. The measurement errors in the emission characteristic parameters in these mass transfer models, i.e., the initial emittable concentration (C ₀), the diffusion coefficient (D), and the partition coefficient (K), can result in errors in predicting indoor VOC and formaldehyde concentrations. These errors have not yet been quantitatively well analyzed in the literature. This paper addresses this by using modelling to assess these errors for some typical building conditions. The error in C ₀, as measured in environmental chambers and applied to a reference living room in Beijing, has the largest influence on the model prediction error in indoor VOC and formaldehyde concentration, while the error in K has the least effect. A correlation between the errors in D, K, and C ₀ and the error in the indoor VOC and formaldehyde concentration prediction is then derived for engineering applications. In addition, the influence of temperature on the model prediction of emissions is investigated. It shows the impact of temperature fluctuations on the prediction errors in indoor VOC and formaldehyde concentrations to be less than 7% at 23±0.5°C and less than 30% at 23±2°C.     

Modelling mixing parameters in concentric-tube airlift bioreactors

Axial dispersion of the liquid phase was investigated in a concentric-tube airlift bioreactor (RIMP: V _L=0.70?m³) as a whole and in the separate zones (riser, downcomer, gas-separator) using the axial dispersion model. The axial dispersion number Bo and the axial dispersion coefficient, D _ax were determined from the output curves to an initial Dirac pulse, using the tracer response technique. They were analyzed in relation to process and geometrical parameters, such as: gas superficial velocity, ν_SGR; top clearance, h _S; bottom clearance, h _B, and resistances at downcomer entrance expressed as A _d/A _R ratio. Correlations between Bodenstein numbers in the overall bioreactor and riser and downcomer sections (Bo_T,Bo_R,Bo_D) and the geometrical and process parameters were developed, which can allow to assess the complex influence of these parameters on liquid axial dispersion.     

Thermodynamics and kinetics of co-operative protein-nucleic acid binding: II. Studies on the binding between protamine and calf thymus DNA

Unspecific binding of a protamine, namely fluorescein-labelled clupeine Z, to double-stranded calf thymus DNA was studied using fluorescence titration methods and chemical relaxation techniques. Both equilibrium and kinetic data have been analysed using general theoretical approaches discussed in the accompanying paper. The results agree well with the predictions made on the basis of a standard co-operative binding model.Basic parameters evaluated are the co-operative binding constant (K), the coefficient measuring co-operative interaction between nearest neighbours (q), the number of nucleotides occupied by one protamine molecule (n) and the rate constant of dissociation at the ends of bound ligand sequences (K_D). Values obtained at 20 °C, pH 7.5 and 0.4 m-NaCl were K = 5.8 × 10⁷m^?1, q = 1700, n = 20 and K_D = 0.29 s^?1. They have been found to be sensitive to the concentration of added salt (NaCl). This effect apparently reflects the essentially electrostatic nature of the binding process. The results can be satisfactorily described in terms of competitive binding of sodium ions.     

Growth Kinetics of Attached Iron-Oxidizing Bacteria

A model of growth and substrate utilization for ferrous-iron-oxidizing bacteria attached to the disks of a rotating biological contactor was developed and tested. The model describes attached bacterial growth as a saturation function in which the rate of substrate utilization is determined by a maximum substrate oxidation rate constant (P), a half-saturation constant (K_s), and the concentration of substrate within the rotating biological contactor (S₁). The maximum oxidation rate constant was proportional to flow rate, and the substrate concentration in the reactor varied with influent substrate concentration (S₀). The model allowed the prediction of metabolic constants and included terms for both constant and growth-rate-dependent maintenance energies. Estimates for metabolic constants of the attached population of acidophilic, chemolithotrophic, iron-oxidizing bacteria limited by ferrous iron were: maximum specific growth rate (μ_max), 1.14 h⁻¹; half-saturation constant (K_s) for ferrous iron, 54.9 mg/liter; constant maintenance energy coefficient (m₁), 0.154 h⁻¹; growth-rate-dependent maintenance energy coefficient (m′), 0.07 h⁻¹; maximum yield (Y_g), 0.063 mg of organic nitrogen per mg of Fe(II) oxidized.     

A structured model for the kinetics of fungal amylase production

Summary The cell is considered to be divided into nucleic acids, proteinaceous material and storage compounds. The enzyme is believed to be constitutive but repressed by the rate of catabolism. A structured model is developed to describe the growth, amylase production and dissolved oxygen profile in the batch culture ofAspergillus oryzae.Nomenclature CA Conc. of enzyme SKB units/m³ - C_D,C_E,C_G,C_O,C_S Conc. of D.E.G. mass, oxygen, substrate kg/m³ - C_O* Mean oxygen conc. in gas-liquid interface kg/m³ - C_X Total cell conc. kg/m³ - D D-mass (proteins) kg - E E-mass (storage carbon) kg - G G-mass (necleic acids) kg - K_E Rate of usage of E-mass kg/m³/h - K_EO K_E with oxygen limitation kg/m³/h - Q Active fraction of promotor genes - - R_D,R_E,R_G Rate of production of D,E,G-mass kg/m³/h - R_O,R_S Rate of usage of oxygen, substrate kg/m³/h - R_DO,R_EO,R_GO R_D,R_E and R_G with oxygen limitation kg/m³/h - S Substrate (carbon) concentration kg/m³ - t Time h - t_o Time at which C_S = 0 h - K₁,K₂,K₃,K₂₄,K₂₅ Stoichiometric constants - - K₄,K₅,K₆,K₇ Rate constants h^–1 - K₈-K₁₂,K₁₈,K₂₀-K₂₃ Michaelis-Menten constants kg/m³ - K₂₆,K₂₆ Absorption coefficient, K₂₆ at C_X = 0 h^–1 - K₂₇ Empirical constant kg/m³ - K₁₅ Rate of enzyme formation SKB units/kg - K₁₆,K₁₇ Equilibrium constants m³/kg - K₁₉ Decay constant for mRNA h^–1     

Localization and characteristics of rat liver mitochondrial aldehyde dehydrogenases.

Two NAD-dependent aldehyde dehydrogenase enzymes from rat liver mitochondria have been partially purified and characterized. One enzyme (enzyme I) has molecular weight of 320,000 and has a broad substrate specificity which includes formaldehyde; NADP is not a cofactor for this enzyme. This enzyme has K_m values for most aldehydes in the micromolar range. The isoelectric point was found to be 6.06. A second enzyme (enzyme II) has a molecular weight of 67,000, a K_m value for most aldehydes in the millimolar range but no activity toward formaldehyde. NADP does serve as a coenzyme, however. The isoelectric point is 6.64 for this enzyme. By utilization of the different substrate properties of these two enzymes it was possible to demonstrate a time-dependent release from digitonin-treated liver mitochondria. The high K_m, low molecular weight enzyme (enzyme II) is apparently in the intermembrane space while the low K_m, high molecular weight enzyme (enzyme I) is in the mitochondrial matrix and is most likely responsible for oxidation of acetaldehyde formed from ethanol.     

Kinetics of Hydrogen Consumption by Rumen Fluid, Anaerobic Digestor Sludge, and Sediment

Michaelis-Menten kinetic parameters for H₂ consumption by three methanogenic habitats were determined from progress curve and initial velocity experiments. The influences of mass transfer resistance, endogenous H₂ production, and growth on apparent parameter estimates were also investigated. Kinetic parameters could not be determined for undiluted rumen fluid and some digestor sludge from gas-phase measurements of H₂, since mass transfer of H₂ across the gas-liquid interface was rate limiting. However, accurate values were obtained once the samples were diluted. H₂ consumption by digestor sludge with a long retention time and by hypereutrophic lake sediment was not phase transfer limited. The K_m values for H₂ uptake by these habitats were similar, with means of 5.8, 6.0, and 7.1 μM for rumen fluid, digestor sludge, and sediment, respectively. V_max estimates suggested a ratio of activity of approximately 100 (rumen fluid):10 (sludge):1 (sediment); their ranges were as follows: rumen fluid, 14 to 28 mM h⁻¹; Holt sludge, 0.7 to 4.3 mM h⁻¹; and Wintergreen sediment, 0.13 to 0.49 mM h⁻¹. The principles of phase transfer limitation, studied here for H₂, are the same for all gaseous substrates and products. The limitations and errors associated with gas phase determination of kinetic parameters were evaluated with a mathematical model that combined mass transport and Michaelis-Menten kinetics. Three criteria are described which can be used to evaluate the possibility that a phase transfer limitation exists. If it does not exist, (i) substrate consumption curves are Michaelis-Menten and not first order, (ii) the K_m is independent of initial substrate concentration, and (iii) the K_m is independent of biomass (V_max) and remains constant with dilution of sample. Errors in the Michaelis-Menten kinetic parameters are caused by endogenously produced H₂, but they were <15% for rumen fluid and 10% for lake sediment and digestor sludge. Increases in V_max during the course of progress curve experiments were not great enough to produce systematic deviations from Michaelis-Menten kinetics.     

Effects of dissolved organic matter from sewage sludge on the atrazine sorption by soils

The effects of dissolved organic matter (DOM), water soluble organic matter derived from sewage sludge, on the sorption of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-trazine) by soils were studied using a batch equilibrium technique. Six paddy soils, chosen so as to have different organic carbon contents, were experimented in this investigation. Atrazine sorption isotherms on soils were described by the linear equation, and the distribution coefficients without DOM (K_d) or with DOM (K_d ^*) were obtained. Generally, the values of K_d ^*/K_d initially increased and decreased thereafter with increasing DOM concentrations of 0–60 mg DOC · L^?1 in soil-solution system form. Critical concentrations of DOM (DOM_np) were obtained where the value of K_d ^* was equal to K_d. The presence of DOM with concentrations lower than DOM_np promoted atrazine sorption on soils (K_d ^* > K_d), whereas the presence of DOM with concentrations higher than DOM_np tended to inhibit atrazine sorption (K_d ^* < K_d). Interestingly, DOM_np for tested soils was negatively correlated to the soil organic carbon content, and the maximum of K_d ^*/K_d (i.e.K _max) correlated positively with the maximum of DOM sorption on soil (X_max). Further investigations showed that the presence of hydrophobic fraction of DOM evidently promoted the atrazine sorption on soils, whereas the presence of hydrophilic DOM fraction obviously tended to inhibit the atrazine sorption. Interactions of soil surfaces with DOM and its fractions were suggested to be the major processes determining atrazine sorption on soils. The results of this work provide a reference to the agricultural use of organic amendment such as sewage sludge for improving the availability of atrazine in soils.     

A convenient analysis of Michaelis enzyme kinetic progress curves based on second derivatives

A simple method is described for the estimation of the Michaelis parameters, K_m and V_m, from a single progress curve at a single substrate concentration without the need to follow the reaction to completion. By measuring the substrate concentration and the time when the second derivative is at a minimum, K_m and V_m can be easily obtained.     

Microbial oxidation of methanol: Purification and properties of formaldehyde dehydrogenase from a Pichia sp. NRRL-Y-11328

An NAD⁺-linked, reduced glutathione-dependent formaldehyde dehydrogenase was purified to homogeneity from soluble extracts of methanol-grown yeast, Pichia sp. Formaldehyde and methylglyoxal are oxidized in the presence of NAD⁺ as an electron acceptor. NADP⁺ could not replace NAD⁺. Other straight chain aldehydes (C₂–C₆ tested), branched-chain aldehydes (e.g., isobutyaldehyde), aromatic aldehydes (e.g., salicylal-dehyde, benzaldehyde), glutyraldehyde, glyceraldehyde, glycoaldehyde, and glyoxal-dehyde tested were not oxidized by the purified formaldehyde dehydrogenase. The product of formaldehyde oxidation by purified enzyme was demonstrated to be S-for-mylglutathione by measuring the absorption at 240 nm due to the formation of thioester of formaldehyde and reduced glutathione. The K_m values for NAD⁺, formaldehyde, and reduced glutathione were 0.12, 0.31, and 0.16 mm, respectively, for the forward reaction at pH 8.0. The purified formaldehyde dehydrogenase also catalyzed the reduction of S-formylglutathione in the presence of NADH. Formate was not reduced by the purified enzyme. The K_m values for S-formylglutathione and NADH were 0.60 and 0.25 mm, respectively, for the reverse reaction at pH 6.0. Formaldehyde dehydrogenase has a molecular weight of 84,000 as determined by gel filtration and subunit molecular weight of 41,000 as determined by sodium dodecyl sulfate-gel electrophoresis. S-Formylglutathione, a product of formaldehyde oxidation, was oxidized by the partially purified formate dehydrogenase from Pichia sp. Formate dehydrogenase has a higher affinity toward S-formylglutathione (K_m value 1.8 mm) than toward formate (K_m value 25 mm). Antiserum prepared against the purified formaldehyde dehydrogenase from Pichia sp. NRRL-Y-11328 forms strong precipitin bands with isofunctional enzymes from methanol-grown Pichia pastoris NRRL-Y-7556 and Torulopsis candida Y-11419 and weak precipitin bands with Hansenula polymorpha NRRL-Y-2214. No cross-reaction was observed with isofunctional enzyme derived from methanol-grown Kloeckera sp.     

Esterification and hydrolysis of vitamin A in the liver of brook trout (Salvelinus fontinalis) and the influence of a coplanar polychlorinated biphenyl

Recent reports of extremely low retinoid stores in fish living in contaminated river systems prompted an initial investigation of the mechanisms of hepatic storage and mobilization in brook trout. Enzyme characterization in microsomes revealed a lecithin:retinol acyltransferase activity (LRAT) optimum in the alkaline range (pH 9.0; V_max=0.6 nmol per mg prot. h⁻¹; K_m=10.2 μM) which is not known to occur in mammals, in addition to a secondary optimum at pH 6.5 typical of mammals. Acyl CoA:retinol acyltransferase (ARAT) kinetic parameters were quite different to those of mammals. The substrate affinity of trout ARAT (K_m=1.6 μM) was approximately 22-fold greater than that of the rat while maximal velocity (V_max=0.2 nmol per mg prot. h⁻¹) was 18-fold less. Retinyl ester hydrolase activity (REH) was optimal under acid conditions (pH 4.2; V_max=6.6 nmol per mg prot. h⁻¹; K_m=0.6 mM), was inhibited by a bile salt analogue and was greater in males than females. This REH was tentatively categorized as a bile salt-independent, acid retinyl ester hydrolase (BSI-AREH). REH was inhibited in a dose-dependent manner following in vivo exposure to a representative environmental contaminant the coplanar polychlorinated biphenyl (PCB), 3,3′,4,4′-tetrachlorobiphenyl (TCBP). Inhibition may be an indirect effect because enzyme activity was not affected by in vitro exposure of control microsomes. REH inhibition in the brook trout may affect the uptake of retinyl esters (REs) from chylomicron remnants as well as the mobilization of stored REs.     

A novel method for characterisation of microbial growth kinetics on volatile organic compounds

A novel method for the determination of microbial growth kinetics on hydrophobic volatile organic compounds (VOC) has been developed. A stirred tank reactor was operated as a fed-batch system to which the VOC was continuously fed via the gas phase, assuring a constant VOC concentration in the mineral medium. A flow of air was saturated with the VOC, and then mixed with a further flow of air, to obtain a predetermined VOC concentration. Thus, different VOC concentrations in the mineral medium could be obtained by altering the VOC concentration in the feed gas. The growth kinetics of Xanthobacter autotrophicus GJ10 on 1,2-dichloroethane (DCE) and of Pseudomonas sp. strain JS150 on MonoChloroBenzene (MCB) were assessed using this method. The growth of strain JS150 was strongly inhibited at MCB concentrations higher than 160 mg l⁻¹, and the results were fitted using a piecewise function. The growth kinetics of strain GJ10 were described by the Luong model where maximum growth rate μ_max = 0.12 h⁻¹, substrate saturation constant K _S = 7.8 mg l⁻¹, and maximum substrate concentration S _m (above which growth is completely inhibited) = 1080 mg l⁻¹. Varying nitrogen and oxygen flows enabled the effect of oxygen concentration on the growth kinetics of Pseudomonas JS150 to be determined. Received: 30 November 1998 / Received revision: 19 March 1999 / Accepted: 20 March 1999     

The influence of external potassium on the inactivation of sodium currents in the giant axon of the squid, Loligo pealei

Isolated giant axons were voltage-clamped in seawater solutions having constant sodium concentrations of 230 mM and variable potassium concentrations of from zero to 210 mM. The inactivation of the initial transient membrane current normally carried by Na⁺ was studied by measuring the Hodgkin-Huxley h parameter as a function of time. It was found that h reaches a steady-state value within 30 msec in all solutions. The values of h _∞, τ_h, α_h,and β_h as functions of membrane potential were determined for various [K _o]. The steady-state values of the h parameter were found to be inversely related, while the time constant, τ_h, was directly related to external K⁺ concentration. While the absolute magnitude as well as the slopes of the h _∞ vs. membrane potential curves were altered by varying external K⁺, only the magnitude and not the shape of the corresponding τ_h curves was altered. Values of the two rate constants, α_h and β_h, were calculated from h_∞ and τ_h values. α_h is inversely related to [K_o] while β_h is directly related to [K_o] for hyperpolarizing membrane potentials and is independent of [K_o] for depolarizing membrane potentials. Hodgkin-Huxley equations relating α_h and β_h to E_m were rewritten so as to account for the observed effects of [K_o]. It is concluded that external potassium ions have an inactivating effect on the initial transient membrane conductance which cannot be explained solely on the basis of potassium membrane depolarization.     

A least-squares method for fitting the Hill equatio to data from several animals.

The principle of the method is to solve a set of nonlinear simultaneous equations, given initial estimates of the nonlinear parameters (h, the Hill coefficient, and K, the substrate constant). It can be adapted to fit the Hill equation to sets of data with common values of h and K but different maximum velocities, and an example of this is given. The method is compared with some published alternatives.     

Development and validation of high-performance size exclusion chromatography methods to determine molecular size parameters of Haemophilus influenzae type b polysaccharides and conjugates

Current vaccines against Haemophilus influenzae type b (Hib) consist of the polyribosyl ribitol phosphate (PRP) capsular polysaccharide chemically conjugated to a carrier protein. Among the various biological and physical analyses to be performed on these vaccines, the determination of the molecular size of the polysaccharide preparations throughout the conjugation process is particularly relevant. Comparison of results from high-performance size exclusion chromatography (HPSEC) with those routinely obtained using conventional gel permeation chromatography (CGPC) methods highlights the correlation between the two methods for determining the values of the chromatographic distribution coefficient (K_D) of native and activated polysaccharides. The resulting data showed that the K_D value is sufficient to characterize these polysaccharides using an HPSEC method. However, additional molecular size parameters (i.e., molar mass and hydrodynamic radius) are necessary for a reliable characterization of the tetanus conjugate (PRP-T), certainly due to the lattice-like structure of the conjugate. In practice, an absolute detection system in HPSEC composed of a low-angle light scattering detector, a viscometer, and a refractive index (RI) detector was used. As demonstrated, these HPSEC methods are rapid, accurate, and reproducible for the polysaccharides and their glycoconjugates and provide a relevant and more informative alternative to the current CGPC methods.     

The effects of hypothyroidism and fasting on electrogenic amino acid transfer: Possible evidence for multiple neutral amino acid carrier systems in rat jejunum

The jejunal mechanisms for the electrogenic transfer of four neutral amino acids (alanine, leucine, methionine, valine) and for sarcosine were characterised by an electrical method in vitro. The values for apparent K_m obtained electrically agree well with those assessed by conventional chemical techniques. Hypothyroidism and/or fasting rats for 3 days induced differential changes in the apparent K_m and p.d._max for the various amino acids. These alterations were interpreted as indicating the presence of at least three mechanisms for neutral amino acid transfer and one for sarcosine.In euthyroid rats, only alanine showed changes in apparent K_m (decrease) and p.d._max (decrease) after fasting for 3 days. With hypothyroidism the kinetic parameters of electrogenic transfer for alanine, valine and sarcosine were significantly altered while those for leucine and methionine were unaffected.     

Solvent isotope effects on α-glucosidase

The solvent kinetic isotope effects (SKIE) on the yeast α-glucosidase-catalyzed hydrolysis of p-nitrophenyl and methyl-d-glucopyranoside were measured at 25 °C. With p-nitrophenyl-d-glucopyranoside (pNPG), the dependence of k_cat/K_m on pH (pD) revealed an unusually large (for glycohydrolases) solvent isotope effect on the pL-independent second-order rate constant, ^DOD(k_cat/K_m), of 1.9 (±0.3). The two pK_as characterizing the pH profile were increased in D₂O. The shift in pK_a2 of 0.6 units is typical of acids of comparable acidity (pK_a=6.5), but the increase in pK_a1 (=5.7) of 0.1 unit in going from H₂O to D₂O is unusually small. The initial velocities show substrate inhibition (K_is/K_m～200) with a small solvent isotope effect on the inhibition constant [^DODK_is=1.1 (±0.2)]. The solvent equilibrium isotope effects on the K_is for the competitive inhibitors d-glucose and α-methyl d-glucoside are somewhat higher [^DODK_i=1.5 (±0.1)]. Methyl glucoside is much less reactive than pNPG, with k_cat 230 times lower and k_cat/K_m 5×10⁴ times lower. The solvent isotope effect on k_cat for this substrate [=1.11 (±0. 02)] is lower than that for pNPG [=1.67 (±0.07)], consistent with more extensive proton transfer in the transition state for the deglucosylation step than for the glucosylation step.     

Oxidation of formaldehyde by alcohol oxidase of Candida boidinii

A formaldehyde oxidase activity was found in cell-free extracts of methanol-grown yeast Candida boidinii. Loss of alcohol oxidase activity in a mutant, 4₈, led to loss of the formaldehyde oxidase activity, indicating that the same enzyme is probably responsible for both activities. This could be demonstrated with the purified alcohol oxidase which oxidizes, besides lower primary alcohols, formaldehyde to formate. The K _m value for formaldehyde is 5.7 mM. It seems that alcohol oxidase is not implicated in formaldehyde oxidation in vivo.     

PqqD Is a Novel Peptide Chaperone That Forms a Ternary Complex with the Radical S-Adenosylmethionine Protein PqqE in the Pyrroloquinoline Quinone Biosynthetic Pathway

Pyrroloquinoline quinone (PQQ) is a product of a ribosomally synthesized and post-translationally modified pathway consisting of five conserved genes, pqqA-E. PqqE is a radical S-adenosylmethionine (RS) protein with a C-terminal SPASM domain, and is proposed to catalyze the formation of a carbon-carbon bond between the glutamate and tyrosine side chains of the peptide substrate PqqA. PqqD is a 10-kDa protein with an unknown function, but is essential for PQQ production. Recently, in Klebsiella pneumoniae (Kp), PqqD and PqqE were shown to interact; however, the stoichiometry and K_D were not obtained. Here, we show that the PqqE and PqqD interaction transcends species, also occurring in Methylobacterium extorquens AM1 (Me). The stoichiometry of the MePqqD and MePqqE interaction is 1:1 and the K_D, determined by surface plasmon resonance spectroscopy (SPR), was found to be ∼12 μm. Moreover, using SPR and isothermal calorimetry techniques, we establish for the first time that MePqqD binds MePqqA tightly (K_D ∼200 nm). The formation of a ternary MePqqA-D-E complex was captured by native mass spectrometry and the K_D for the MePqqAD-MePqqE interaction was found to be ∼5 μm. Finally, using a bioinformatic analysis, we found that PqqD orthologues are associated with the RS-SPASM family of proteins (subtilosin, pyrroloquinoline quinone, anaerobic sulfatase maturating enzyme, and mycofactocin), all of which modify either peptides or proteins. In conclusion, we propose that PqqD is a novel peptide chaperone and that PqqD orthologues may play a similar role in peptide modification pathways that use an RS-SPASM protein.