Glutaraldehyde--its purity and stability

A portable EIS-based biosensor for the detection of microcystin-LR residues in environmental water bodies and simulated body fluids

Due to the eutrophication of water bodies around the world, there is a drastic increase in harmful cyanobacterial blooms leading to contamination of water bodies with cyanotoxins. Chronic exposure to cyanotoxins such as microcystin leads to oxidative stress, inflammation, and liver damage, and potentially to liver cancer. We developed a novel and easy-to-use electrochemical impedance spectroscopy-based immunosensor by fabricating stencil-printed conductive carbon-based interdigitated microelectrodes and immobilising them with cysteamine-capped gold nanoparticles embedded in polyaniline. It has been also coupled with a custom handheld device enabling regular on-site assessment, especially in resource-constrained situations encountered in developing countries. The sensor is able to detect microcystin-LR up to 0.1 μg L-1, having a linear response between 0.1 and 100 μg L-1 in lake and river water and in serum and urine samples. In addition to being inexpensive, easy to fabricate, and sensitive, it also has very good selectivity.

Portable biosensor for the detection of Enrofloxacin and Ciprofloxacin antibiotic residues in food, body fluids, environmental and wastewater samples

Enrofloxacin (ENR) and its metabolite Ciprofloxacin (CIP) are both a class of fluoroquinolone antibiotics effective against a broad-spectrum microbial infection. Recent surge in the consumption of CIP and ENR has been linked to increased cases of drug-resistant pathogens. This is due to the fact that the antibiotic residues remain in milk, meat, soil and environmental water for a prolonged duration. Although gold standard methods such as LC-MS are sensitive, they suffer from expensive operation and maintenance cost, and would need dedicated facilities and tedious sample preparation steps. Such limitations make on site detection impossible for regulatory bodies in developing countries. To address this issue, we developed a portable device that can detect the presence of CIP and ENR antibiotics in the range of parts per billion (ppb) concentrations accurately. It consists of a polyaniline (PAni) coated U-bent optical fiber with anti-ENR/CIP antibody immobilized on the polymer surface. The sensor relies on the principle of evanescent wave absorbance by antigen-antibody complex. The sensor showed limit of detection (LOD) of 1 ppb with a linear range of operation from 1 ppb to 500 ppb (R2 = 0.96-0.99) in lake water, waste water treatment plant effluent, urine, blood serum, milk and meat samples. The recovery of the sensor ranges from 88% to 120% indicating reasonable accuracy. The sensor has excellent selectivity towards CIP and ENR and showed stability for four weeks indicating its field deployability and robustness. The portable sensor is scalable and contract has been given to an industry partner to mass manufacture the device.

Biochemical synthesis of palladium nanoparticles: The influence of chemical fixatives used in electron microscopy on nanoparticle formation and catalytic performance

Palladium nanoparticles (PdNPs) can catalyse a range of reductive chemical reactions transforming both organic and inorganic environmental pollutants. PdNPs that ranged from <2 to 2-40 nm were synthesized using chemical methods, and bacterial biomass with/without chemical fixatives. PdNP formation was enhanced by adsorption of Pd(II) to bacterial biomass, followed by fixation with formate or glutaraldehyde. TEM-SAED analyses confirmed that the cell associated PdNPs were polycrystalline with a face-centered cubic structure. Chemically formed PdNPs possessed a higher Pd(0):Pd(II) ratio and produced structurally similar nanoparticles as the biotic systems. These PdNPs were employed to catalyze two, reductive chemical reactions, transforming 4-nitrophenol (4-NP) and hexavalent chromium [Cr(VI)], into 4-aminophenol and Cr(IV), respectively. In the reduction of 4-NP, the catalytic performance was directly proportional to PdNP surface area, i.e., the smallest PdNPs in formate-PdCH34 cells had the fastest rate of reaction. The mass of Pd(0) as PdNPs was the main contributor to Cr(VI) reduction; the chemically synthesized PdNPs showed the highest removal efficiency with 96% at 20 min. The use of glutaraldehyde enhanced the reduction of Pd(II) and promoted PdNPs formation, i.e., creating an artefact of fixation; however, this treatment also enhanced the catalytic performance of these PdNPs.

Glutaraldehyde - A Subtle Tool in the Investigation of Healthy and Pathologic Red Blood Cells

Glutaraldehyde is a well-known substance used in biomedical research to fix cells. Since hemolytic anemias are often associated with red blood cell shape changes deviating from the biconcave disk shape, conservation of these shapes for imaging in general and 3D-imaging in particular, like confocal microscopy, scanning electron microscopy or scanning probe microscopy is a common desire. Along with the fixation comes an increase in the stiffness of the cells. In the context of red blood cells this increased rigidity is often used to mimic malaria infected red blood cells because they are also stiffer than healthy red blood cells. However, the use of glutaraldehyde is associated with numerous pitfalls: (i) while the increase in rigidity by an application of increasing concentrations of glutaraldehyde is an analog process, the fixation is a rather digital event (all or none); (ii) addition of glutaraldehyde massively changes osmolality in a concentration dependent manner and hence cell shapes can be distorted; (iii) glutaraldehyde batches differ in their properties especially in the ratio of monomers and polymers; (iv) handling pitfalls, like inducing shear artifacts of red blood cell shapes or cell density changes that needs to be considered, e.g., when working with cells in flow; (v) staining glutaraldehyde treated red blood cells need different approaches compared to living cells, for instance, because glutaraldehyde itself induces a strong fluorescence. Within this paper we provide documentation about the subtle use of glutaraldehyde on healthy and pathologic red blood cells and how to deal with or circumvent pitfalls.

A simplified method of preparation of mammalian intestine samples for scanning electron microscopy

Due to strong tissue hydration and complex architecture of the mucous membrane, appropriate preparation of inhomogeneous gastrointestinal tissues, especially from the intestine, for scanning electron microscopy is still a challenge and requires constant improvement of preparation techniques. In this article, we describe a simplified method of preparation of small intestinal mucosa tissues for observations in a scanning electron microscope. We emphasized the most important points in the preparation process that, when ignored, may result in formation of numerous artifacts and the inability to analyze the samples reliably. The developed technique facilitates proper animal tissue sampling in the field conditions, reducing the time of tissue collection and sample preparation as well as the total process costs. The fixative of choice, that is, buffered formalin, fixes, and stiffens the processed tissues properly, which is especially important in preservation of long, highly hydrated intestinal villi without shrinkage artifacts. The method described has been successfully used in comparative studies of the development of small intestines in mammals (pigs, mice, rats), reptiles, and birds (hens).

Novel poly(ε-caprolactone)/gelatin wound dressings prepared by emulsion electrospinning with controlled release capacity of Ketoprofen anti-inflammatory drug

In the present study, a single and binary Ketoprofen-loaded mats of ultrathin fibers were developed by electrospinning and their physical properties and drug release capacity was analyzed. The single mat was prepared by solution electrospinning of poly(ε-caprolactone) (PCL) with Ketoprofen at a weight ratio of 5wt%. This Ketoprofen-containing PCL solution was also used as the oil phase in a 7:3 (wt/wt) emulsion with gelatin dissolved in acidified water. The resultant stable oil-in-water (O/W) emulsion of PCL-in-gelatin, also containing Ketoprofen at 5wt%, was electrospun to produce the binary mat. Cross-linking process was performed by means of glutaraldehyde vapor on the electrospun binary mat to prevent dissolution of the hydrophilic gelatin phase. The performed characterization indicated that Ketoprofen was successfully embedded in the single and binary electrospun mats, i.e. PCL and PCL/gelatin, and both mats showed high hydrophobicity but poor thermal resistance. In vitro release studies interestingly revealed that, in comparison to the single PCL electrospun mat, the binary PCL/gelatin mat significantly hindered Ketoprofen burst release and exhibited a sustained release capacity of the drug for up to 4days. In addition, the electrospun Ketoprofen-loaded mats showed enhanced attachment and proliferation of L929 mouse fibroblast cells, presenting the binary mat the highest cell growth yield due to its improved porosity. The here-developed electrospun materials clearly show a great deal of potential as novel wound dressings with an outstanding controlled capacity to release drugs.

Novel DNA Staining Method and Processing Technique for the Quantification of Undamaged Double-stranded DNA in Epidermal Tissue Sections by PicoGreen Probe Staining and Microspectrophotometry

Histotechnological processing of DNA can cause damage to and loss of DNA and can change its structure. DNA probes have severe tissue-staining limitations. New DNA probes and improved histotechnology are needed to enhance the characterization of fixed tissue-bound DNA. Our team developed a novel DNA staining technique and histotechnological processing procedure that improves tissue-bound DNA retention and the qualification and quantification of intact double-stranded (ds)-B-DNA. We used the ultrasensitive PicoGreen ds-DNA probe for the histochemical characterization of ds-DNA. Fifteen fixatives were examined to determine which were best for preventing DNA denaturation and retaining original DNA content and structures. Our use of a microwave–vacuum oven reduced heating temperatures, shortened heating and processing times, and enhanced fixation. We achieved better qualitative and quantitative results by using superior tissue-acquisition techniques (e.g., reduced prefixation times) and improved histotechnology. We also compared our novel approach with archival tissues, delayed fixation, less sophisticated and conventional histological processing techniques, and by experimenting with preservation of tissue-bound ds-Z-DNA. Results demonstrate that our histotechnological procedure and nucleic acid staining method significantly improve the retention of intact, undamaged ds-DNA which, in turn, allows the investigator to more precisely quantify the content and structures of unaltered and undamaged tissue-bound ds-B-DNA. (J Histochem Cytochem 55: 999–1014, 2007)

Preparation of Cross-Linked Cellulase Aggregates onto Magnetic Chitosan Microspheres

The cellulase was immobilized onto magnetic chitosan microspheres carrier as cross-linked enzymes aggregates (CLEAs). It was precipitated with 95% saturation ammonia sulfate and cross-linked with 3% (v/v) glutaraldehyde. Efficient enzyme activity about 50.6% was obtained when cellulase concentration was 1.0mg/mL after cross-linking for 7 h at 30○C. The CLEAs was advantageous on stabilities and magnetic responsiveness for separation.

Hemoglobin (Hb) immobilized on amino-modified magnetic nanoparticles for the catalytic removal of bisphenol A

Catalytic removal of bisphenol A from aqueous solution with hemoglobin immobilized on amino-modified magnetic nanoparticles as an enzyme catalyst was reported. The amino-modified magnetite nanoparticles were firstly prepared by the coprecipitation of Fe(2+) and Fe(3+) with NH(3)·H(2)O and then modified by 3-aminopropyltriethoxysilane. The immobilization process was optimized by examining enzyme concentration, glutaraldehyde concentration, cross-link time, and immobilization time. The optimum conditions for the removal of bisphenol A with immobilized hemoglobin were also investigated. Under the optimality conditions, the removal efficiency of bisphenol A was about 80.3%. The immobilization had a beneficial effect on the stability of hemoglobin and conversions of bisphenol A. According to the proposed breakdown pathway and the intermediates, the enzyme-catalytic removal of bisphenol A by the immobilized hemoglobin is considered to be an effective method.

Raising antibodies by coupling peptides to PPD and immunizing BCG-sensitized animals

The use of PPD (purified protein derivative of tuberculin) as a carrier has several significant advantages. It provides very powerful T cell help and it gives rise to virtually no antibody response against itself. This is particularly useful if it is intended to go on to make monoclonal antibodies, where the presence of a large amount of anti-carrier antibody is a nuisance! Furthermore, unlike most comparably powerful adjuvant systems, it can be used in man. PPD coupling has been used to raise antibodies to haptens and to raise T cell responses to tumour cells. It is here reported that small peptides coupled to PPD will give rise to good titres of anti-peptide antibody. For peptides that contain no cysteine, coupling has been achieved by attaching succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC) to the alpha-amino group of the peptide and N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) to the PPD and allowing an uncleavable bond to form between them. Data on immunization with the leucotactic nonapeptide of the alpha chain of the complement component C3 and with some oncogene-related peptides have been obtained.

Bioartificial materials based on collagen: 1. Collagen cross-linking with gaseous glutaraldehyde

The effect of exposure time of thin films of soluble collagen to glutaraldehyde (GTA) vapour was studied at 37 degrees C, and was evaluated by examining the thermal and biological stability and the swelling ratio. It was found that the collagen films treated with GTA vapour for 18 h showed the highest denaturation temperature, the lowest swelling ratio, and an enhanced proteolytic stability. This study shows that soluble collagen can be effectively cross-linked with GTA vapour and that the degree of cross-linking can be controlled by varying the exposure time.

An evaluation of polyamine immunocytochemistry using immunocytochemical model systems

Polyamine (PA) immunocytochemistry (ICC) was evaluated by a recently developed enzyme-linked immunosorbent assay (ELISA) binding test (ELISABT) using an anti-spermine (Spm) serum raised against Spm conjugated via the cross-linker N-(gamma-maleimidobutyryloxy)succinimide (GMBS) with bovine serum albumin. In the test the antiserum showed strong immunoreactivity with N1-acetylspermine (Ac-Spm) and acetylspermidine (N1-Ac-Spd and N8-Ac-Spd), and low immunoreactivity with Spm and Spd, which was, however, markedly enhanced after reaction with GMBS, acetic anhydride or glutaraldehyde. Complete agreement with results of immunoblot analysis was observed. PA-like immunoreactivity observed in the present PA ICC in cells in the foveolae and isthmus of rat gastric glands was completely abolished by absorption of the serum with N1,N12-diacetyl-Spm, Ac-Spm or N1-Ac-Spd, but not by Spm or Spd. This absorption test was then simulated by an ELISA inhibition test (ELISAIT) with a solid phase conjugated with Ac-Spm or Spm, and by a PA ICC model system using Sepharose gel beads conjugated with each of several PAs. The results strongly suggest that the immunostaining in the gastric mucosa was mainly due to antibody species in the serum specific to 'acylated' Spm and Spd, but not to Spm or Spd. Acetyl PAs exist at such low concentrations in animal tissues that they are virtually undetectable by current ICC methods. Therefore Spm and Spd are likely candidates for those detected, after having been converted by fixation into such PA derivatives as become reactive with the antiserum.

Preparation and characterization of albumin-heparin microspheres

Albumin-heparin microspheres were prepared by a two-step process which involved the preparation of a soluble albumin-heparin conjugate, followed by formation of microspheres from this conjugate or by a double cross-linking technique involving both coupling of soluble albumin and heparin and microsphere stabilization in one step. The first technique was superior since it allowed better control over the composition and the homogeneity of the microspheres. Microspheres could be prepared with a diameter of 5-35 microns. The size could be controlled by adjusting the emulsification conditions. The degree of swelling of the microspheres was sensitive to external stimuli, and increased with increasing pH and decreasing ionic strength of the medium.

Cholesterol and 25-hydroxycholesterol retention in specimens of liver and aorta prepared for electron microscopy. I. Standard fixation methods and metabolism of the labeled sterols

In the present work, several preparatory procedures commonly used for electron microscopy (EM) were evaluated as to their ability to preserve cholesterol (CHO) and CHO derivatives in tissue. We also determined in several rat tissues to what extent the sterols used as tracers are metabolized. Sprague-Dawley rats were injected intraperitoneally with [1 alpha,2 alpha(n)-3H]cholesterol ([3H]CHO) and 25-hydroxy-[26,27-3H]cholesterol ([3H]25-OH-CHO). Lipids of the liver, aorta and brain were extracted one and five days after injection, and the distribution of the labeled lipids was followed by thin-layer chromatography. When labeled CHO was injected as tracer, most of the radioactivity remained associated with the CHO fraction. When 25-hydroxycholesterol (25-OH-CHO) was used, we found that it was mostly metabolized to yield more polar compounds. Our results show that the loss of CHO and CHO derivatives from tissues depends not only on the preparatory procedure used for EM, but also on the type of tissue studied.

Cholesterol and 25-hydroxycholesterol retention in specimens of liver and aorta prepared for electron microscopy. II. Effect of filipin, osmium, digitonin and saponin

Sprague-Dawley rats were injected intraperitoneally with [1 alpha, 2 alpha(n)-3H]cholesterol or 25-hydroxy-[26,27-3H]cholesterol, and one and five days later liver and aortic tissues were fixed. The extent to which these sterols were lost from the tissues during preparation for electron microscopy (EM) was examined utilizing different fixation procedures and various protective agents. Radioactive tracers, scintillation counting and standard EM techniques were used. Although most of the procedures examined caused major lipid losses, useful fixation procedures that allow retention of cholesterol or 25-hydroxy-cholesterol in liver and aortic tissues were found and are described here.

A critical review of the toxicology of glutaraldehyde

Glutaraldehyde, a low molecular weight aldehyde, has been investigated for toxicity in humans and animals. Examination of this dialdehyde was indicated from previous studies with other aldehydes in which carcinogenicity of formaldehyde and toxicity of acetaldehyde and malonaldehyde have been disclosed. Information gaps concerning the actions of glutaraldehyde have been identified in this review and recommendations are suggested for additional short- and long-term studies. In particular, information regarding irritation of the respiratory tract, potential neurotoxicity, and developmental effects would assist in a complete hazard evaluation of glutaraldehyde. Further study related to disposition, metabolism, and reactions of glutaraldehyde may elucidate the mechanism of action.

An efficient enzyme immunoassay for glutamate using glutaraldehyde coupling of the hapten to microtiter plates

In order to coat microtiter plates for enzyme immunoassays (EIAs), amino acids and other haptens are usually coupled to larger protein molecules. The formation of such conjugates is not always reproducible. This may lead to inconsistent hapten-protein stoichiometries, unfavorable orientation of the hapten on the protein and/or well-to-well variation in the concentration of the available hapten. In the assay described here the excitatory amino acid (EAA) Glu is coupled directly to polystyrene microtiter wells with GA. Each step of the assay was tested for maximum efficiency. The resulting EIA with Glu as a competitor gave excellent reproducibility (coefficient of variation = 5.87%), an EC50 of 2.02 X 10(-5) M and a detection limit of 1.26 X 10(-6) M. This EIA method is generally useful for a variety of antisera to amino acids and small peptides and a wide range of competing substances. It can be used to characterize the conformational requirements for antigen binding, to assay for glutamate or to identify compounds with glutamate-like structure in unknown solutions.

The prevention of adsorption of interferents to radiolabelled protein by Tween 20

Radiolabels are often used to quantitatively determine the amount of protein immobilized on chromatographic supports, immunochemical plates and biosensor surfaces. Bovine serum albumin (BSA) was chosen as a model protein for quantitative deposition studies. BSA was radioiodinated (125I-) or fluorescently labelled (fluorescein), then incubated with the following surfaces: quartz, quartz derivatized by 3-aminopropyltriethoxysilane (Qz-APTES), and Qz-APTES reacted with glutaraldehyde or tresyl chloride. The amounts of BSA immobilized to the different surfaces were compared using data from radioactivity and fluorescence assays. Irreproducible results were obtained with radioiodinated BSA due to adsorption/desorption behaviour of an unidentified radioactive species. When the non-ionic detergent Tween 20 was added to the protein/surface incubation mixture, radiolabelled BSA gave reproducible protein binding results which agreed with fluorescent protein binding patterns. The effect of Tween 20 was due to either the binding to BSA displacing the interferent and/or the solubilization of the interferent.

Separation of glutaraldehyde and some of its aldol condensation products by hydroxyl-aldehyde group affinity chromatography

Glutaraldehyde exists in aqueous solution in equilibrium with monomers and polymers of cyclic and open-chain hemialdals and hydrates. At alkaline pH oligomeric and polymeric alpha,beta-unsaturated aldehyde derivatives are formed from primarily produced aldol condensation products. This communication reports a method for separation of such aldol condensates by means of a new high performance liquid chromatography technique based on the affinity of aldehyde groups for hydroxyl groups of a hydroxylated polyether matrix (Bio-Gel SEC-10). Five peaks corresponding to different aldol condensates of glutaraldehyde were obtained from the affinity column. They have been distinguished by 1H-NMR and UV spectroscopy. Kinetic measurements yielded formation rates for the different aldol condensates.

Biochemical changes and cytotoxicity associated with the degradation of polymeric glutaraldehyde derived crosslinks

The reversibility of glutaraldehyde crosslinks has been suggested as a reason for failure of long-term bioprosthetic implants. The stability of such crosslinks was investigated in tendons and model compounds. Small but cytotoxic levels of glutaraldehyde were still released from crosslinked tendons even after these tendons were extensively rinsed for up to 6 months. The toxic effect was evidenced by the death of fibroblasts surrounding a midsection piece of rinsed crosslinked tendon, while the end section pieces did not show toxic effects. The formation and stability of glutaraldehyde modified [14C]-L-lysine derivatives were investigated. The polymerization of glutaraldehyde with amino compounds was initially fast but continued to proceed slowly for months. Degradation of high-molecular-weight soluble polymers was detected by gel filtration chromatography. Low-molecular-weight soluble materials were also released from insoluble products which were formed when high concentrations of glutaraldehyde and radioactive lysine were reacted. These chemical and biological studies suggest that local cytotoxicity of glutaraldehyde crosslinked bioprostheses may be due to unstable glutaraldehyde polymers that persist in the interstices of crosslinked tissues.

The effect of heating by microwave irradiation and by conventional heating on the aldehyde concentration in aqueous glutaraldehyde solutions

The effect of short time heating of aqueous solutions of glutaraldehyde (GA) on relative aldehyde concentration was determined using spectrophotometric analysis. Because free monomeric GA absorbs U.V. light at 280 nm, whereas the alpha, beta polymeric forms absorb at 235 nm, the purity of GA solutions can be expressed as the ratio: A 235 nm/A 280 nm (purification index, P.I.). Heating of 4 ml aliquots of 0.85% distilled aqueous GA solution resulted in an increase of the absorption at 280 nm which is correlated positively with temperature. No increase of absorption at 235 nm was found when solutions were kept at 40 degrees C for several hours. The increase of absorption at 280 nm is caused by a rapid decyclization of hemiacetals producing an increase in free aldehyde concentration. No major differences in absorption were found between the solutions heated by microwave and by conventional heating. However, because microwave irradiation is known to produce an homogeneous rise in temperature, especially in bulky samples, it is expected that the results of fixation procedures will improve by the combined effect of higher temperature and enhanced diffusion rates of the fixating species.

The preparation and physicochemical characterization of an injectable form of reconstituted, glutaraldehyde cross-linked, bovine corium collagen

Pepsin-solubilized bovine corium collagen was purified, reconstituted, and treated with various levels of glutaraldehyde. Treatment of suspensions of fibrillar collagen with low concentrations of glutaraldehyde appeared to have little effect on the gross morphology of fibrils, as judged by electron microscopy, but did have a significant impact on their physicochemical stability. Fibrillar collagen treated with glutaraldehyde at a concentration equal to or greater than 0.0075% demonstrated significant decreases in neutral solubility at elevated temperatures as compared to noncross-linked controls. Differential scanning calorimetry provided a convenient and quantitative means to correlate increases in melting temperature with increases in glutaraldehyde treatment concentration. Fibrillar collagen cross-linked with glutaraldehyde concentrations as low as 0.0075% demonstrated a significantly greater resistance to proteolytic degradation than did noncross-linked fibrillar collagen samples. The residual, extractable aldehyde content of such preparations was between 1 and 3 ppm. Rheological measurements on such cross-linked suspensions demonstrated that they were non-Newtonian, shear-thinning fluids, and that they were two- to threefold more viscous than corresponding preparations of noncross-linked collagen.

A rapid method for obtaining monomeric glutaraldehyde

A new method for the distillation of glutaraldehyde to obtain the monomeric form is presented. The monomer is obtained after only one distillation and it has a purification index (Pi) smaller than 0.20.

Laboratory preparation and evaluation of a multiparameter hemocytometry control

A protocol for the laboratory preparation of a multiparameter hemocytometry control is given. Human platelets, stabilized by a basically simplified and inexpensive fixation procedure, are added to our previously described white and red blood cell control. Evaluation of this multiparameter control shows good precision characteristics and acceptable mechanical stability for at least 7 weeks, as measured in the Coulter counter Model S Plus-II. The control can basically contribute to the realization of the essence of internal quality control: continuous self-auditing and continuous attempts at improvement of performance.

Studies on the phenazine methosulphate-tetrazolium salt capture reaction in NAD(P)+-dependent dehydrogenase cytochemistry. I. Localization artefacts caused by the escape of reduced co-enzyme during cytochemical reactions for NAD(P)+-dependent dehydrogenases

The correct localization of oxidative enzymes using cytochemical tetrazolium methods, in which low molecular weight electron carriers such as NAD(P)H and reduced phenazine methosulphate (PMSH) are used, can be endangered by the escape of the reduced intermediates before they react to form the insoluble formazan at the true enzyme-containing sites. To investigate this phenomenon, the glucose-6-phosphate dehydrogenase reaction was studied in fixed erythrocytes which, because of their microscopic dimensions, are well-suited for studying the loss of intermediates. A mixture of active and heat-inactivated fixed erythrocytes was incubated in a PMS-supplemented medium for glucose-6-phosphate dehydrogenase. The cytophotometric histograms showed that the final formazan precipitate was equally distributed over both active and inactivated cells. When bovine serum albumin was added to the medium, all the formazan was found to be bound to this protein and the erythrocytes remained essentially unstained. The false localization in this system could be explained by an unfavourable balance between the capture of electrons carried by NADPH within the erythrocyte and the diffusion of NADPH out of the erythrocyte. The rate constant of NADPH oxidation was determined, as was also the diffusion constant of NADPH in a protein matrix. Substituting the data obtained into formulae derived from the enzyme cytochemical localization theory of Holt & O'Sullivan (1958), it was calculated that the capture reaction was highly deficient and, theoretically, less than 1% of the total amount of formazan produced was localized within the erythrocyte which explains the false localization observed. The importance of these findings for the cytochemical demonstration of NAD(P)+-dependent dehydrogenases in cells and electropherograms is briefly discussed.

A simple post-embedding system for the rapid demonstration of tissue antigens under the electron microscope

A simple and versatile technique for the preparation of ultra-thin sections, which can be stained immunohistochemically directly on electron microscope grids, is presented. An anti-hapten immunoperoxidase procedure has been adapted for use on tissue fixed in a purified monomeric glutaraldehyde--picric acid mixture, and embedded in 'L R White', a recently formulated plastic resin. This plastic tolerates the use of partial dehydration of tissue, resulting in higher antigenic yields. In addition, no etching of ultra-thin sections is necessary, and the whole immunostaining procedure can be completed in less than 2 h. A comparison of commonly used fixatives is discussed. High-resolution micrographs showing general staining (uranyl acetate--lead citrate) of rat pancreas, and immunostaining of insulin and TSH in storage granules in perfusion-fixed rat tissue and of lambda-chain immunoreactive cells in immersion-fixed human tonsil are included as examples.

Vascular reactions to perfusion fixation

Vascular reactions to fixation with a 2 x 5% w/v glutaraldehyde fixative were studied in a constant flow perfusion system on isolated rabbit intestines and hind limb preparations. Reactions induced by the fixative were compared to reactions induced by noradrenaline in each single preparation. Changes in vascular resistance were assessed from continuous recordings of arterial and venous pressures and perfusion flow. Changes in vascular filtration and macromolecular permeability during fixation were approximated from recordings of flow and measurements of concentrations of dextran in the perfusate at the arterial inlet and at the venous outlet. Our results indicate that the vascular bed of the preparations studied can be reliably fixed in a high resistance state of smooth muscle activity induced by noradrenaline as well as in a low resistance state in the absence of noradrenaline, provided that hydrodynamic parameters are strictly controlled. The vascular filtration decreases during fixation. In optimally perfused preparations 5-10 min are required to fully saturate the binding capacity of the tissue for glutaraldehyde. Data on viscosity and colloid osmotic pressure of Tyrode solution containing dextran T-70 in various concentrations, and of various aldehyde-containing fixatives in 0 . 1 M sodium phosphate buffer with and without dextran added, are given.

Effect of pyridine homologues on proton flux through the CF0 . CF1 complex and photophosphorylation in chloroplasts

At concentrations below 1 mM, hydrophobic pyridine homologues decrease the rate of photophosphorylation and light-stimulated hydrolysis of ATP and light-activated exchange of the tightly bound nucleotides in chloroplasts, but increase the rate of the Hill reaction. Unlike uncoupling agents, the presence of the organic base at such low concentrations decreases the rate of light-dependent leakage and has no effect on the efficiency of two-stage photophosphorylation in broken chloroplasts. By assuming that the organic base is bound to independent equivalent sites in the thylakoid membrane, a simple expression can be derived which relates the observed rates of photophosphorylation and light-stimulated hydrolysis of ATP quantitatively to the concentration of the organic base in solution and gives dissociation equilibrium constants which are on the order of the relative hydrophobicities of the pyridine homologues. A possible mechanistic model for the CF0 . CF1 complex is proposed which could serve as the basis for a unified interpretation of the kinetics of proton translocation in illuminated chloroplasts, the steady-state rate of photophosphorylation, the light-stimulated ATPase activity, and the light-activated exchange of tightly bound adenine nucleotides.

Effects of different fixative solutions on labeling of concanavalin-A receptor sites in human T-lymphocytes

We have studied the effect of several fixative solutions on the number of Concanavalin-A (Con-A) receptor sites of human peripheral blood T-lymphocytes. Cells treated with different fixative solutions (glutaraldehyde (G); formaldehyde (F) G+F; osmium tetroxide (Os); Os+G; Os+F; and Os+G+F) were labeled with a Con-A gold labeled horseradish peroxidase (HRP) complex and the number of gold particles on the lymphocytic surface was evaluated. Comparison of cells treated with the different fixatives used showed significant differences in the density of labeling. After G fixation the number of gold particles was lower than after fixation with Os or F. Moreover, G used in combination with F or Os reduced the labeling obtained when the two latter fixatives were used alone.

Methods in ultrastructural cytochemistry of the cell nucleus

The electron microscopical study of the cell nucleus as observed in thin sections requires the use of cytochemical methods because of the intricate pattern of the nuclear components. The in situ techniques based on electron staining and enzymatic digestion are reviewed, excluding autoradiography, cytoenzymology and immunocytochemistry. A tentative classification has been adopted according to the chemical nature of the revealed component. Thus, the staining procedures for the nucleoproteins in general, for both nucleic acids, for the proteins, and finally for the deoxyribonucleoproteins and DNA are considered separately. 1--Stains for the nucleoproteins include simple reagents such as the uranyl and lead salts which are largely used in electron microscopy but are of limited specificity. 2--A variety of methods, some of them specific, is available for the simultaneous visualization of DNA and RNA which is based on common properties: basophilia, ability to bind diaminoacridines, presence of hydroxyl groups. However, due to the recent development of specific and preferential methods for each nucleic acid, we feel that among the older methods, only rapid and simple procedures for the detection of both nucleic acids remain of interest. 3--Proteins being ubiquitous, the useful techniques must reveal subsets within the total nuclear proteins. Apart from some endogeneous enzymes, basic proteins -- practically histones -- so far represent the only group for the detection of which reliable methods exist. 4--Several techniques developed recently are available for the specific detection of DNA. In favourable cases, methods derived from the Feulgen reaction allow its visualization at a molecular level. In addition, standard procedures for the preparation of mammalian cells and tissues are described. Each staining method is at least briefly discussed, but emphasis has been placed on a small number of techniques described in detail. They comprise the EDTA regressive stain for the ribonucleoproteins, several reactions of the basic proteins and the Feulgen-like osmium ammine reaction for DNA.