Absence Of Dye Research Articles

Cotton Dyeing with Vat Dyes using Alkaline Pectinase and Iron (II) Salt

Use of sodium hydrosulfite in the dyeing of cotton with vat dyes is criticized for generation of sulfur compounds leading to air and water pollution. In this study, attempts were made to dye cotton with alkaline pectinase along with iron (II) salt as an alternative formulation. A 43 Box-Behnken design was used for statistical analysis of performance for this new reducing system and to obtain optimum parameters for cotton dyeing. The results showed that alkaline pectinase along with iron (II) salt was quite effective in developing comparable dyebath potential, dye receptivity on cotton with comparable dye strength, and colorfastness, as compared to the hydrosulfite-based reducing system. Dyebath stability in presence and absence of dye also showed superior results compared to that of the hydrosulfite system.

Hybrid system of photocatalytic fuel cell and Fenton process for electricity generation and degradation of Reactive Black 5

Abstract A novel hybrid system composed of a photocatalytic fuel cell (PFC) and Fenton reactor was developed with the aim to degrade the azo dye Reactive Black 5 (RB5) and generate electricity. Compared to previously established system of bioelectro-Fenton system, microbial fuel cell (MFC) system has significant challenge in the development and operation system. Therefore, PFC is used instead of MFC to generate electrons for the Fenton system. The effect of azo dye (RB5) on each PFC and Fenton reactor was investigated. The experimental results showed that maximum power output was achieved in the absence of dye in the Fenton reactor of this hybrid system. Furthermore, higher degradation efficiency of RB5 could also be observed in the PFC reactor in this hybrid system.

Dye-surfactant aggregates as corrosion inhibitor for mild steel in NaCl medium: Experimental and theoretical studies

Abstract The corrosion inhibition efficiency of tetradecyltrimethylammonium bromide (TTAB) in presence of Sunset Yellow (SY) was investigated in NaCl corrosive medium using Tafel linear polarization method, electrochemical impedance spectroscopy (EIS), gravimetric measurement, and Density functional theory (DFT) calculations. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and UV–visible spectroscopy techniques were also employed to study the morphology of corrected surface and the nature of adsorbed layer. It was revealed that TTAB micelles exhibit low corrosion inhibition efficiency at high concentration for mild steel in NaCl, while the inhibition efficiency was drastically increased in TTAB-SY mixed system, reaching higher than 90% in the presence of 100 uM TTAB- SY(1:1). Different corrosion mechanisms were proposed in the presence and absence of dye. A noticeable Warburg resistance was observed in the absence of dye while no Warburg was seen in the presence of dye indicating that the mechanism is mainly changed. Also, the results indicated that TTAB-SY ion pairs act as mixed-type inhibitors. Finally, from the optimized geometry of TTAB, SY, and TTAB-SY complexes and also electron distribution in HOMO and LUMO, possible modes of interaction of TTAB-SY complexes with mild steel surface have been predicted.

Electrogeneration of Active Chlorine in a Filter-Press-Type Reactor Using a New Sb2O5Doped Ti/RuO2-ZrO2Electrode: Indirect Indigoid Dye Oxidation

AbstractThis paper presents the study on active chlorine mediated electrochemical oxidation of model solutions that simulate textile effluents containing an indigoid dye (indigo carmine) and sodium chloride (0.05 M) using a new Sb2O5-doped Ti/RuO2-ZrO2electrode. The study was carried out in a filter-press electrochemical reactor specially designed to minimize flow deviations and provide homogeneous mass transfer flux over the electrode surface. Firstly, the mass-transfer-limited chloride oxidation reaction was studied in the absence of dye in order to understand the active chlorine formation process. Changes in pH, chloride concentration and UV-visible absorption spectra during electrolysis reveal the formation of active chlorine (mainly hypochlorite) with current efficiencies for chloride oxidation of 0.558 and 0.503 at 10 and 20 mA cm−2, respectively. Secondly, chloride oxidation was investigated in the presence of indigo carmine dye (0.5 mM) wherein-situgenerated active chlorine was responsible for -C=C- bond breaking and dye degradation. The solution discoloration followed a pseudo-first order kinetics where kinetic coefficient was inversely proportional to dye concentration. The oxidation with active chlorine had an average efficiency of 0.7 and a very competitive energy consumption between 49.2 and 128.5 kW h (kg COD removed)−1depending on current density and flow rate.

Cationic Comb-Type Copolymer Excludes Intercalating Dye from DNA Without Inducing DNA Condensation

The interaction of a single molecule of DNA with cationic comb-type copolymers has been observed using a flow-stretch assay. We have shown that interaction with a copolymer with a high degree of grafting did not cause a coil-to-globule transition but resulted in shrinkage of the DNA by 20%. In this study, a flow-stretch assay was employed in which changes in length and fluorescence intensity of DNA were simultaneously observed. Upon binding of fluorescent intercalator dyes, the DNA length was extended. In the presence of copolymer, dye binding was inhibited and DNA length was not significantly different than that in the absence of dye and copolymer. Our data suggest that the copolymer does not influence DNA length. Our observation implies that use of the fluorescence dye exclusion assay to estimate DNA condensing activity of polycations must be carefully carried out. Keywords: Coil-to-globule transition, Compaction, DNA, Flow-stretch, Graft copolymer, Inter polyelectrolyte complex, Polycation, Singlemolecular observation.

Investigations of the interaction and phase transfer to a TiO2 surface of water soluble dyes with polyelectrolyte/surfactant complexes using ultraviolet–visible spectroscopy and multivariate least squares analysis

Interactions of polyelectrolyte/surfactant complexes (PSCs) with the ionic dyes phenol red (PR) and bromothymol blue (BB) and the adsorption of these dyes to a TiO2 surface were studied using ultraviolet–visible (UV–vis) spectroscopy. The PSC consisted of the polyelectrolyte sodium polystyrene-4-sulfonate (PSS) and the surfactant cetylpyridinium bromide monohydrate (CPBM). For the studies involving PR the PSC began to extract the PR from solution at an absolute mol ratio of CPBM to PSS greater than 300:1 but more CPBM needs to be added to the solution to maximize the removal of the PR. The number of PR molecules per PSC was calculated to be 20±2 for solutions of 5×10−7M PSS and 11±1 for 1×10−6M PSS. For the PR experiments the number of CPBM molecules per PSC was calculated to be 250±20 for 5×10−7M PSS solutions and 300±20 for 1×10−6M PSS solutions. For studies involving BB the PSC begins to extract the BB from solution at an absolute mole ratio of CPBM to PSS of greater than 280:1. Unlike the PR this extraction is essentially complete for the BB by an absolute mole ratio of CPBM to PSS of 320:1 indicating that the BB interacts more strongly with the PSC than does the PR. The number of BB molecules per PSC was calculated to be 20±2 for solutions of 5×10−7M PSS and the number of CPBM molecules per PSC was calculated to be 300±20 for 5×10−7M PSS solutions. The Δ(ΔG) between the complex formed with the BB and the PR was estimated to be −1.6±0.4kJ/mol. The aggregation behavior of the CPBM and PSS in the absence of the dyes was found to be drastically different compared to the studies with the dyes present. In the absence of either dye the number of CPBM molecules per PSC was calculated to be 150±10 for 5×10−7M PSS.

Potentiometric study of cetylpyridinium chloride cooperative binding to anionic azo-dyes

The binding of cetylpyridinium chloride (CPC) with some azo dyes (X6G, 3-BL, DY-42) has been extensively studied at various concentration of dyes, using cetylpyridinium-selective membrane electrode as a fast and accurate method. Klotz logarithmic plots have been constructed from EMF measurements. These plots indicated cooperativity in all of interactions. The accurate binding isotherms have been obtained and analyzed using Hill equation. The values of Hill equation parameters have been estimated and determined by considering this fact that saturation parameter of binding in the Hill equation (y) can be determined from the ratio of electromotive force (EMF) measurements in the presence and absence of dye. In all of the interactions Hill coefficients indicate cooperative binding in CPC-dye interactions due to the combination of both electrostatic and hydrophobic interactions. Intrinsic Gibbs energies of binding processes have been also calculated and interpreted on basis of interaction mechanism.

Thermally Stimulated Current analysis of ZnO Functional Thin Film in the presence and absence of Dye

Thermally Stimulated Current analysis of ZnO Functional Thin Film in the presence and absence of Dye

Overlap of laccases/cellobiose dehydrogenase activities during the decolourisation of anthraquinonic dyes with close chemical structures by Pycnoporus strains

Pycnoporus strains were used as model to understand the role of laccases in the in vivo decolourisation of three anthraquinonic dyes. The decolourisation capability of Pycnoporus sanguineus MUCL 41582 (PS7), which produces laccases as the main oxidative enzyme, was assayed and compared with the decolourisation capability of a control strain, Pycnoporus cinnabarinus MUCL 39533 (PC330) described as laccase-deficient strain. In absence of dye, laccase activity was observed during the trophophase and the idiophase with PS7, while no laccase activity was observed with PC330. Acid Blue 62 (ABu62), Acid Blue 281 (ABu281) and Reactive Blue 19 (RBu19) caused an increase in laccase activity and surprisingly laccase activity was detected with PC330. In vitro, oxidation of all three anthraquinones by a laccase preparation was obtained to a lesser extent than the whole cell process; suggesting that other factor(s) could be required for a complete decolourisation. As the time space of laccase production in the tested fungi was not perfectly coincidental with the decolourisation process, the activity of cellobiose dehydrogenase (CDH) was monitored. Present early in the broth during the growth of the fungi, CDH displayed in vitro a synergism with laccases in the decolourisation of ABu62, and an antagonism with laccases in the decolourisation of ABu281 and RBu19.

The effect of reactive dyes upon the uptake and antibacterial efficacy of poly(hexamethylene biguanide) on cotton. Part 3: Reduction in the antibacterial efficacy of poly(hexamethylene biguanide) on cotton, dyed with bis(monochlorotriazinyl) reactive dyes

The antibacterial efficiency of poly(hexamethylene biguanide), PHMB, on un-dyed cotton has been compared with that of PHMB on cotton coloured with a range of reactive dyes. In each case, the presence of covalently bound dye resulted in a reduction in antibacterial efficiency. In the absence of dye, the cationic PHMB binds to the cotton via weak ion–ion linkages with the carboxylate groups present on cotton; these dissociate readily allowing release of free PHMB, the active antibacterial agent. In the presence of reactive dye, the cationic PHMB forms stronger ion–ion linkages with the strong sulphonic acid groups of the dyes; thus release of free PHMB, the active agent, is less facile and antibacterial efficiency reduced accordingly.

Helical Disposition of Proteins and Lipopolysaccharide in the Outer Membrane ofEscherichia coli

In bacteria, several physiological processes once thought to be the products of uniformly dispersed reactions are now known to be highly asymmetric, with some exhibiting interesting geometric localizations. In particular, the cell envelope of Escherichia coli displays a form of subcellular differentiation in which peptidoglycan and outer membrane proteins at the cell poles remain stable for generations while material in the lateral walls is diluted by growth and turnover. To determine if material in the side walls was organized in any way, we labeled outer membrane proteins with succinimidyl ester-linked fluorescent dyes and then grew the stained cells in the absence of dye. Labeled proteins were not evenly dispersed in the envelope but instead appeared as helical ribbons that wrapped around the outside of the cell. By staining the O8 surface antigen of E. coli 2443 with a fluorescent derivative of concanavalin A, we observed a similar helical organization for the lipopolysaccharide (LPS) component of the outer membrane. Fluorescence recovery after photobleaching indicated that some of the outer membrane proteins remained freely diffusible in the side walls and could also diffuse into polar domains. On the other hand, the LPS O antigen was virtually immobile. Thus, the outer membrane of E. coli has a defined in vivo organization in which a subfraction of proteins and LPS are embedded in stable domains at the poles and along one or more helical ribbons that span the length of this gram-negative rod.

Latent-image formation in tabular AgBr grains: experimental studies

Five tabular-grain AgBr emulsions of varying grain thickness were studied. Two were chemically sensitized in the presence of a blue spectral sensitizing dye, whereas the other three were chemically sensitized in the presence of a green spectral sensitizing dye. A companion set of emulsions chemically sensitized in the absence of dye was also prepared. Internal image development of the unsensitized emulsions showed substantial internal image in one emulsion, but minor amounts in the other emulsions. After chemical sensitization, there was no detectable internal image in any of the emulsions. Reciprocity failure data from 10−4 to 103 s showed that the emulsions sensitized in the presence of dye had little if any high-irradiance reciprocity failure, suggesting the minimum developable size of the latent image was three atoms for the development conditions used. Low-irradiance reciprocity failure commenced at 0.1–1 s. Long wavelength sensitivity studies showed that the chemical sensitization generally enhanced the sensitivity of three spectral regions in the emulsions sensitized in the absence of dye—550, 650 and 750 nm. These spectral regions are suggested to coincide with three distinct states of the sensitizer centres. Data for the emulsions chemically sensitized in the presence of dye were limited owing to the interference by dye absorption. The temperature dependence of the long wavelength sensitivity showed the activation energy for this process increased as the wavelength increased. Quantum sensitivity measurements were also made at the midpoint of the D−logE curve using 0.1 s exposures. Neglecting the polydisperse nature of these emulsions, values were 10–19 absorbed photons/grain for 400-nm exposures and 13–27 absorbed photons/grain for spectral exposures. An energy-level diagram was constructed for the emulsions sensitized in the absence of dye using their measured activation energies and the photon energies of the three spectral regions. The 550 centre is most likely a single-sulphide or single-selenide centre, with an unknown gold content and provides a shallow electron trap (0.1 eV maximum depth). The compositions of the 650 and 750 centres are most likely multiple sulphide or selenide or sulphide–selenide with unknown gold content. They provide deeper electron traps of depth 0.225–0.425 eV (650 centre) and 0.45–0.65 (750 centre), with the 650 centre probably the dominant of the two in terms of concentration.

Diffusion coefficients for direct dyes in aqueous and polar aprotic solvents by the NMR pulsed-field gradient technique

The nuclear magnetic resonance pulsed-field gradient (NMR-PFG) technique was applied to determine the diffusion coefficients of selected direct dyes, including Congo Red, in D 2O and a deuterated polar aprotic solvent (DMSO- d 6). In addition, the self-diffusion coefficients of the solvents were determined in the presence and absence of dye, to reveal solvent–dye interactions. Diffusion coefficients ranged from about 1.7×10 −10 to 4.4×10 −8 depending on the dye, temperature and solvent employed. It is proposed that dye aggregation exists in DMSO- d 6 and D 2O, with the level of aggregation depending on the temperature and dye.

Atomic Force Microscopy of Nonhydroxy Galactocerebroside Nanotubes and Their Self-Assembly at the Air–Water Interface, with Applications to Myelin

Myelin is one of the few biological membranes to contain the lipid galactocerebrosides, although their role in myelin is unclear. To explore its structural role, we used fluorescence and atomic force microscopy (AFM) to study nonhydroxy galactocerebrosides (NCer) at the air–water interface of a Langmuir–Blodgett trough. Fluorescence microscopy at the air–water interface indicated that NCer forms micrometer scale domains of varying radii with six fractal-like extensions. Atomic force microscopy using TappingMode in water on samples transferred to mica confirmed the fractal-like domain structure in the absence of dye and showed that the domains consisted of many aggregated nanotubes with a diameter of 30 nm. The Hausdorf fractal dimension was estimated to be 1.26 and 1.11 for two domains imaged with AFM. This evidence indicates that NCer forms a bulk phase of nanotubes at the air–water interface, unlike the liquid-condensed phase of a phospholipid monolayer. That NCer forms bilayer nanotubes that aggregate strongly suggests NCer helps maintain the stability of myelin by contributing to the curvature and adhesion of the membrane. We found that NCer appears to be decreased in myelin from multiple sclerosis normal appearing white matter, which could be an important event in the loss of myelin stability.

Prediction of emulsion color from droplet characteristics: dilute monodisperse oil-in-water emulsions

The influence of droplet characteristics on the transmission of light through dilute monodisperse oil-in-water emulsions was investigated in the presence and absence of dye. The turbidity spectra and tristimulus color coordinates ( L*, a*, b*) of a series of n-hexadecane oil-in-water emulsions with different disperse phase volume fractions ( φ=0–0.02 wt%), mean droplet radii ( r=0.1–1 μm) and red dye concentration (0 and 0.002 wt%) were measured. The dependence of the optical properties of colored and non-colored emulsions on droplet size and concentration could be qualitatively described by light scattering theory. Nevertheless, there was relatively poor quantitative agreement between theory and experiment because of the influence of the measurement system on the optical properties of emulsions. The information presented in this paper will facilitate the formulation of dilute food and beverage emulsions with specific optical characteristics.

The effect of Nd:YAG pulse duration on dentine crater depth

Objectives: The effect of alteration of laser parameters on laser–dentine interaction, in particular the effect of pulse duration, has not been well documented. The aim of this in vitro study was to determine the effect on dentine crater depth of Nd:YAG laser pulse duration, and total delivered energy, dentine site and the presence or absence of dye. Methods: Ninety-six sound third molars were extracted and sectioned transversely to provide 192 upper and lower cut surfaces. The upper surfaces were painted with a layer of dye (IR5) suitable for absorption at 1064 nm. The specimens were divided into 16 sub-groups and exposed to two Nd:YAG lasers; one of pulse duration 7 ms and the second of pulse duration 35 ps. Both lasers operated in a non-contact mode (spot diameter 165 μm) with repetition rates of 10.5 and 10 Hz, respectively. Four total energies (2.28, 2.64, 3.6, 4.2 J) were delivered to eight dyed and eight undyed sub-groups. Eight outer and five inner sites were irradiated on each specimen. Dentine crater depth was measured five times using a Reflex Microscope and a three-dimensional centre of gravity derived. An upper and lower specimen were taken from each sub-group and viewed under a SEM. Results: ANOVA and multiple regression analysis were applied and the following factors were found to have a statistically significant effect on crater depth ( p<0.0001): total delivered energy, pulse duration and inner/outer location. Conclusions: Increasing energy and pulse duration produced deeper craters. Similarly inner dentine sites produced deeper crater depths. Only craters produced at the ms pulse duration were carbonised. It would appear that laser–dentine interaction has a non-thermal component at picosecond pulse duration.

Optical properties of oil-in-water emulsions containing titanium dioxide particles

The influence of titanium dioxide particles ( d 32=0.62 μm, φ=0–0.3 wt%) on the spectral reflectance and tristimulus color coordinates ( L, a, b) of n-hexadecane oil-in-water emulsions ( d 32=0.29 μm, φ=0.25–20 wt%) was measured in the absence and presence of a red dye. There was a steep decrease in the spectral reflectance and ‘lightness’ of emulsions at droplet concentrations below 3 wt% and in titanium dioxide suspensions at particle concentrations below 0.1 wt%. In the absence of dye, dilute emulsions ( φ<3 wt%) could be produced with approximately the same color ( L, a, b) as concentrated emulsions by adding 0.1 wt% titanium dioxide. In the presence of dye, a higher concentration (>0.3 wt%) of titanium dioxide was required to match the color of dilute emulsions to concentrated ones. There was reasonable agreement between the measured optical properties of emulsions containing titanium dioxide and those predicted by light scattering theory. These results have important consequences for optimizing the appearance of emulsion-based products with reduced droplet concentrations, e.g. low-fat foods.

Proton and electron transfer during the reduction of molecular oxygen by fully reduced cytochrome c oxidase: a flow-flash investigation using optical multichannel detection.

Proton and electron transfer events during the reaction of solubilized fully reduced bovine heart cytochrome c oxidase with molecular oxygen were investigated using the flow-flash technique. Time-resolved spectral changes resulting from ligand binding and electron transfer events were detected simultaneously with pH changes in the bulk. The kinetics and spectral changes in the visible region (450-750 nm) were probed by optical multichannel detection, allowing high spectral resolution on time scales from 50 ns to 50 ms. Experiments were carried out in the presence and absence of pH-sensitive dyes (carboxyfluorescein at pH 6.5, phenol red at pH 7.5, and m-cresol purple at pH 8.5) which permitted separation of spectral changes due to proton transfer from those caused by ligand binding and electron transfer. The transient spectra recorded in the absence of dye were analyzed by singular-value decomposition and multiexponential fitting. Five apparent lifetimes (0.93 microseconds, 10 microseconds, 36 microseconds, 90 microseconds, and 1.3 ms at pH 7.5) could consistently be distinguished and provided a basis for a reaction mechanism consistent with our most recent kinetic model [Sucheta, A., Szundi, I., and Einarsdóttir, O. (1999) Biochemistry 37, 17905-17914]. The dye response indicated that proton uptake occurred concurrently with the two slowest electron transfer steps, in agreement with previous results based on single-wavelength detection [Hallén, S., and Nilsson, T. (1992) Biochemistry 31, 11853-11859]. The stoichiometry of the proton uptake reactions was approximately 1.3 +/- 0.3, 1.4 +/- 0.3, and 1.6 +/- 0.5 protons per enzyme at pH 6.5, 7.5, and 8.5, respectively. The electron transfer between heme a and CuA was limited by proton uptake on a 90 microseconds time scale. We have established the lower limit of the true rate constant for the electron transfer between CuA and heme a to be approximately 2 x 10(5) s-1.

Interaction of the neuronal marker dye FM1-43 with lipid membranes: Thermodynamics and lipid ordering

The fluorescent dye FM1-43 labels nerve terminals in an activity-dependent fashion and has been found increasingly useful in exploring the exo- and endocytosis of synaptic vesicles and other cells by fluorescence methods. The dye distributes between the aqueous phase and the lipid membrane but the physical-chemical parameters characterizing the adsorption/partition equilibrium have not yet been determined. Fluorescence spectroscopy alone is not sufficient for a detailed elucidation of the adsorption mechanism since the method can be applied only in a rather narrow low-concentration window. In addition to fluorescence spectroscopy, we have therefore employed high sensitivity isothermal titration calorimetry (ITC) and deuterium magnetic resonance ( 2H-NMR). ITC allows the measurement of the adsorption isotherm up to 100 μM dye concentration whereas 2H-NMR provides information on the location of the dye with respect to the plane of the membrane. Dye adsorption/partition isotherms were measured for neutral and negatively-charged phospholipid vesicles. A non-linear dependence between the extent of adsorption and the free dye concentration was observed. Though the adsorption was mainly driven by the insertion of the non-polar part of the dye into the hydrophobic membrane interior, the adsorption equilibrium was further modulated by an electrostatic attraction/repulsion interaction of the cationic dye ( z=+2) with the membrane surface. The Gouy-Chapman theory was employed to separate electrostatic and hydrophobic effects. After correcting for electrostatic effects, the dye-membrane interaction could be described by a simple partition equilibrium ( X b= Kc dye) with a partition constant of 10 3–10 4 M −1, a partition enthalpy of Δ H=−2.0 kcal/mol and a free energy of binding of Δ G=−7.8 kcal/mol. The insertion of FM1-43 into lipid membranes at room temperature is thus an entropy-driven reaction following the classical hydrophobic effect. Deuterium nuclear magnetic resonance provided insight into the structural changes of the lipid bilayer induced by the insertion of FM1-43. The dye disturbed the packing of the fatty acyl chains and decreased the fatty acyl chain order. FM1-43 also induced a conformational change in the phosphocholine headgroup. The −P-N + dipole was parallel to the membrane surface in the absence of dye and was rotated with its positive end towards the water phase upon dye insertion. The extent of rotation was, however, much smaller than that induced by other cationic molecules of similar charge, suggesting an alignment of FM1-43 such that the POPC phosphate group is sandwiched by the two quaternary FM1-43 ammonium groups. In such an arrangement the two cationic charges counteract each other in a rotation of the −P-N + dipole.

Reconstitution of membrane-integrated quinoprotein glucose dehydrogenase apoenzyme with PQQ and the holoenzyme's mechanism of action.

Membrane-integrated quinoprotein glucose dehydrogenase from Acinetobacter calcoaceticus was produced by heterologous expression of the gene for it in an Escherichia coli recombinant strain. The apoenzyme (lacking the cofactor pyrroloquinoline quinone, PQQ) was solubilized with Triton X-100 and purified to homogeneity. Reconstitution of the apoenzyme to full activity in the assay was achieved with a stoichiometric amount of PQQ in the presence of Mg2+. Just as for other PQQ-containing dehydrogenases where Ca2+ fulfills this role, Mg2+ anchors PQQ to the mGDH protein and activates the bound cofactor. This occurs in a precise way since high anomer specificity was found for the enzyme toward the sugars tested. Although the steady-state-type kinetics were as expected for a dye-linked dehydrogenase (ping-pong) and the PQQ in it was present in oxidized form, addition of glucose to the holoenzyme resulted in a very slow but continuous production of gluconolactone; i.e., the reaction did not stop after one turnover, with O2 apparently acting as an (albeit poor) electron acceptor by reoxidizing PQQH2 in the enzyme. The surprisingly low reactivity with glucose, in the absence of dye, as compared to the activity observed in the steady-state assay appeared to be due to formation of an anomalous enzyme form, mGDH. Formation of normal holoenzyme, mGDH, reducing added glucose immediately to gluconolactone (in one turnover), was achieved by treating mGDH with sulfite, by reconstituting apoenzyme with PQQ in the presence of sulfite, or by applying assay conditions to mGDH (addition of PMS/DCPIP). As compared to other quinoprotein dehydrogenases, mGDH appears to be unique with respect to the mode of PQQ-binding, as expressed by the special conditions for reconstitution and the absorption spectra of the bound cofactor, and the reactivity of the reduced enzyme toward O2. The primary cause for this seems not to be related to a different preference for the activating bivalent metal ion but to the special way of binding of PQQ to mGDH.