Comparative biochemistry of a cytosolic artiodactyl glycosidase

Artiodactyls possess abundant neutral glycosidase activity in liver, kidney and intestine. This enzyme is cytosolic and displays a more neutral pH optimum, more acidic isoelectric point and broader substrate range than the corresponding acidic beta-galactosidases. The neutral glycosidases were more thermolabile than the respective acidic beta-galactosidases and displayed a relative molecular mass approximating 60 kDa. This isozyme appeared to be a minor species in both rat and dog liver. The porcine enzyme was studied in more detail. Porcine neutral glycosidase activity was detected in 45-day gestational fetuses in both liver and kidney but not brain. Fetal kidney activities were about half those observed in adult kidney extracts. Porcine neutral glycosidase was immunologically distinct from acidic beta-galactosidase and was immunologically similar to the corresponding isozymes from deer, ovine and bovine liver. Porcine neutral glycosidase was moderately inhibited by D-galactonic acid gamma-lactone and strongly inhibited by D-gluconic acid delta-lactone; however, acidic beta-galactosidase was not inhibited by the delta-lactone. Inhibition by the gamma-lactone was competitive for both enzymes. 4-Methylumbelliferyl-beta-D-galactoside,-glucoside and -xyloside competed for the same active site. A polymorphism for fast- and slow-migrating isozymes of porcine neutral glycosidase was observed, which appeared to be under genetic control.

Inhibitory mechanism of serpins. Identification of steps involving the active-site serine residue of the protease

The role of the protease active-site serine residue in the formation of protease-serpin complexes has been investigated by using a mutant of thrombin in which Ser195 was mutated to alanine (S195A). The structural integrity of S195A was established by examining the kinetics of its interaction with the inhibitor hirudin, which does not have substantial interactions with Ser195. The affinity of S195A for hirudin was only tenfold less than that of thrombin and the kinetic constants for the formation of the S195A-hirudin complex were very similar to those observed with thrombin. In contrast to hirudin, the dissociation constants (Ki) for S195A with serpins (antithrombin, protease nexin-1 and alpha1-antitrypsin with a P1 arginine) were 2 x 10(3) to 2 x 10(5)-fold higher than those observed with thrombin. These results indicate a critical role for interactions with Ser195 in stabilizing the thrombin-serpin complexes. The cofactor heparin compensated partially for the loss of interactions with Ser195; it increased the affinity of S195A for protease nexin-1 and antithrombin by 140-fold and 1000-fold, respectively. In the case of heparin/antithrombin, the increase in affinity could be attributed mainly to interactions outside the active site of S195A. Kinetic studies with antithrombin and protease nexin-1 in the presence of heparin indicated that Ser195 was not involved in any rate-limiting process in the formation of protease-serpin complexes. Interactions with Ser195 increased the stability of the complex by markedly reducing its rate of breakdown rather than by increasing its rate of formation. Overall, the results of the kinetic studies were consistent with a mechanism in which the binding of the protease induces a rate-limiting conformational change in the serpin and interactions with the protease's active-site serine residue, occurring in a subsequent faster step, greatly stabilize the complex.

The interference of penicilloic acids with Karl Fischer titration of penicillins

Phenoxymethylpenicilloic acid monohydrate was titrated with 12 different brands of Karl Fischer reagent. It was shown that only the four pyridine-containing reagents gave correct results for water content, providing that the sample solution was cooled in an ice bath or that the delay time of the amperometric end-point determination was 10 s instead of 30 s, as prescribed by the European Pharmacopoeia. The other reagents always gave results, which were too high. When these reagents were used to titrate the water in sodium amoxicillin, sodium carbenicillin or sodium ticarcillin the same conclusions could be drawn with regard to the accuracy of the results, the usefulness of the reagents and the reaction conditions. These penicillins may contain up to 9% penicilloic acids. The maximum relative error obtained with pyridine-free reagents was about 50% for ticarcillin. It has been confirmed that penicilloic acids interfere with Karl Fischer titration of water and that this interference is greatly dependent on the brand of reagent and on the reaction conditions.

Rapid retrovirus titration using competitive polymerase chain reaction

A quantitative polymerase chain reaction (PCR) procedure has been developed for rapid retrovirus titration. This procedure, which is based on the simultaneous amplification of the sample with known amounts of a competitor DNA fragment (competitive PCR), was used for the quantification of viral RNA genomes in retrovirus-producing cell clone supernatants and of proviral DNA molecules formed at 24 h after infection of different reference cell lines. The results obtained from the analysis of several samples indicated that proviral DNA quantification is in complete agreement with the number of selectable colonies in a standard colony assay. Conversely, the number of viral RNA genomes in the producer cell clone supernatants is a poor predictor of the actual efficiency of infection. Repeated competitive PCR experiments for provirus copy number determination at different times after transduction indicated that the number of proviral DNA molecules remains stable over time, suggesting stable integration into the host genome. The developed procedure is rapid and simple, is applicable to retroviral constructs not containing a selectable gene and can be used to directly measure the efficiency of infection of any target cell type, thus overcoming the problem of the dependency of retroviral titer determination on the rate of expression of a selectable gene and on the efficiency of colony formation of a reference cell line.

Two distinct long-chain-acyl-CoA synthetases in guinea pig Harderian gland

Two distinct long-chain-acyl-CoA synthetases which have different kinetic properties were identified in the guinea pig Harderian gland. One was localized in the microsomes and the other in the mitochondria. The relative V(max) values of the microsomal enzyme were 8.1, 1.7 and 1 and the apparent Km values were 66.7, 12.0 and 30.0 microM for palmitic, linoleic and arachidonic acids, respectively. The relative V(max) values of the mitochondrial enzyme were 2.7, 3.5 and 1 and the apparent Km values were 33.3, 29.9 and 30.0 microM for palmitic, linoleic and arachidonic acids, respectively. The relative V(max) values for the liver microsomal enzyme were 2.0, 2.5 and 1, while those of the liver mitochondrial enzyme were 4.1, 3.9 and 1 with palmitic, linoleic and arachidonic acids, respectively. There were no difference between the microsomal and the mitochondrial enzymes in the liver, regarding apparent Km values; these were 38.4, 29.9 and 22.0 microM for palmitic, linoleic and arachidonic acids, respectively. Thus, the substrate specificity and catalytic rate of the mitochondrial enzyme in Harderian gland for palmitic, linoleic and arachidonic acids were similar to the liver enzyme, but not to the microsomal enzyme in Harderian gland. On the other hand, the antiserum raised against the rat liver enzyme immune-titrated and immuno-blotted the enzymes from Harderian gland microsomes and liver, but not so the enzyme from Harderian gland mitochondria. Thus, the microsomal enzyme in Harderian gland had a common immunogenic epitope(s) with the liver enzyme, but the mitochondrial enzyme did not. The Harderian gland mitochondrial enzyme was a distinct protein from liver enzymes. The catalytic and immunogenic characteristics suggest that the enzyme proteins in the Harderian gland are unique, that is, different from that in the liver. The large V(max) value of the Harderian gland microsomal enzyme for palmitic acid suggests that it contributes to the synthesis of a large amount of the secretory lipid and the high Km value to maintenance of cellular lipid in this organ. The evidence that long-chain-acyl-CoA synthetase in the mitochondria is distinct from that in the microsomes was first found in guinea pig Harderian gland.

Complexometric determination of metal ions by microscopic diffusional titration

Acid/base titrations of pico- and femtoliter microsamples have been performed previously using a diffusional microburet (DMB) for reagent delivery in a simple droplet-heptane system (Gratzl, M.; Yi, C. Anal. Chem. 1993, 65, 2085-2088). The lowest delivery rate achieved with a DMB was about 6 fmol/s, which would correspond to about a 1 microL/year volumetric flow rate with a hypothetical equivalent mechanical delivery scheme (Yi, C.; Gratzl, M. Anal. Chem. 1994, 66, 1976-1982). In this work, the feasibility of complexometric titrations in microscopic samples is explored. Stability of pH in the microdroplets required for different determinations and the effects of DMB shank geometry on titration characteristics are also studied. Diffusional microtitrations of Fe(III), Zn(II), and Cu(II) have been performed with EDTA. Xylenol orange and Eriochrome Black T provide clear color changes at the end point of the respective titrations, despite the microscopic size of the samples (between 16 and 1570 pL, corresponding to diameters between 30 and 144 microns). Random errors of the determinations relative to full scale were 6.6% for Fe(III), 5.8% for Cu(II), and 7.9% for Zn(II). The pH required for EDTA titrations of the individual metal ions stays stable in the acidic range. This makes the microscopic titration of a number of metal ions, such as Fe(III), Fe(II), Cu(II), and Pb(II), feasible in a simple droplet-heptane system without any modification. With a higher density of strongly alkaline buffer droplets (about 100 droplets/mm2) sprayed on the bottom of the Petri dish, or by flushing N2 above the heptane, the microscopic samples can also be kept alkaline despite ambient CO2 present. In this way, Zn(II) can also be titrated in microdroplets, requiring a pH around 10. This work renders it possible to perform a variety of complexometric titrations and other chemical manipulations in microdroplets even if they need to be kept alkaline. Similar titrations in single biological cells to assess intracellular buffer capacities of different metal ions, such as Ca(II) and Mg(II), are underway.

Dissociation of 4-hydroxytamoxifen, but not estradiol or tamoxifen aziridine, from the estrogen receptor as the receptor binds estrogen response element DNA

Estradiol-liganded estrogen receptor (E2-ER) binds EREs with a stoichiometry of one E2-ER dimer per estrogen response element (ERE). In contrast, although 4-hydroxytamoxifen (4-OHT)-liganded ER (4-OHT-ER) binds EREs with high affinity, its saturation ERE binding capacity is consistently half that of E2-ER, giving an apparent stoichiometry of one 4-OHT-ER monomer per ERE. Here we show that one molecule of 4-OHT ligand dissociates from the ER dimer apparently during the process of binding to DNA. Under equilibrium conditions, the type I antiestrogen tamoxifen aziridine (TAz), covalently attached to ER (TAz-ER), binds a single ERE with high affinity (Kd = 0.27 nM), comparable to that of E2-ER and 4-OHT-ER. In contrast to 4-OHT-ER, the ERE binding stoichiometry of TAz-ER was identical to that of E2-ER: one dimeric receptor per ERE. By measuring [3H]ligand that was initially bound to ER, a significant loss of [3H]4-OHT from ER was detected after ERE binding, whereas all [3H]E2 or [3H]TAz remained ER-bound. These results confirm that one molecule of 4-OHT ligand dissociates from the ER dimer as a consequence of ERE binding. Binding of 4-OHT and TAz are likely to induce a conformation in ER dimers that alters their capacity for gene activation. Upon ER binding to DNA, this conformation reveals itself by allowing 4-OHT dissociation, and predictably would allow TAz dissociation were it not bound covalently.

Titration of varicella-zoster virus DNA in throat swabs from varicella patients by combined use of PCR and microplate hybridization

We devised a simple procedure for titration of varicella-zoster virus (VZV) DNA in throat swabs from varicella patients. DNA which was extracted from throat swabs, together with known copy numbers of a cloned VZV DNA fragment, were 10-fold serially diluted and used as template in PCR. The PCR products, after heat denaturation, again serially diluted in 1.5 M NaCl and adsorbed to microplate wells. Then, biotin-labeled DNA probes were hybridized with the immobilized DNA. The hybridization signal was produced by streptavidin-conjugated beta-galactosidase and a fluorogenic enzyme substrate. By comparing the titration curves of a clinical specimen with those of the cloned fragment, of which detection limit was about 10 copies, we estimated the copy numbers of VZV DNA in the specimen. With this technique, we evaluated the degree of potential contagiousness of the patient along the course of infection: we found that varicella patients possessed highest quantity of VZV DNA in the throat on the first day of illness.

Direct measurement via phage titre of the dissociation constants in solution of fusion phage-substrate complexes

Studies of interactions between filamentous fusion phage particles and protein or nucleic acid molecules have gained increasing importance with recent successes of screening techniques based upon random phage display libraries (biopanning). Since a number of different phage are usually obtained by biopanning, it is useful to compare quantitatively the binding affinities of individual phage for the substrate used for selection. A procedure is described for determination of relative dissociation constants (KdRel) between filamentous phage carrying peptide fusions to the coat protein gpIII and substrates in solution. This novel method is based on the measurement of phage titres. Phage selected from a random fusion phage library for binding to a monoclonal antibody or a viral structural protein exhibited KdRel values in the nanomolar and micromolar ranges for their respective substrates, thus validating the method over a wide range of binding affinities.

Use of factorial experimental design to delineate the strong calcium- and pH-dependent changes in binding of human surfactant protein-A to neutral glycosphingolipids--a model for studies of protein-carbohydrate interactions

Human surfactant protein-A (SP-A) is a C-type lectin belonging to the collection supergroup of mammalian lectins. It is produced by alveolar type II cells and has been shown to bind to lactosylceramide (R. A. Childs, J. R. Wright, G. F. Ross, C-T Yuen, A. M. Lawson, C. Chai, K. Drickamer, and T. Feizi (1992) J. Biol. Chem. 267, 9972-9979), galactosylceramide, and gangliotriaosylceramide (Y. Kuroki, S. Gasa, Y. Ogasawara, A. Makita, and T. Akino (1992) Arch. Biochem. Biophys. 299, 261-267). To evaluate the pH- and calcium-dependent binding of SP-A to neutral glycosphingolipids we employed a microtiter plate technique and performed a series of full factorial design experiments using lactosylceramide, galactosylceramide, and gangliotetraosylceramide and native nonderivatized SP-A. The optimal binding conditions were drastically different for these three receptors. At pH 7.4 and at 5 mM Ca concentration the binding affinity of SP-A followed the order galactosylceramide > lactosylceramide > gangliotetraosylceramide. However, this was close to optimal conditions for binding of SP-A to lactosylceramide and at minimum for binding to gangliotetraosylceramide. Binding of SP-A to galactosylceramide was relatively insensitive to pH but increased significantly with increasing Ca concentrations. These experiments using factorial experimental design emphasize the importance of critical interpretation of all earlier studies on protein-carbohydrate interactions especially when transferring experimental data into complex biological systems.

[A microtitration variant of the latex agglutination reaction in the diagnosis of leprosy]

The authors describe the preparation of antigenic diagnostic agent based on stained polyacrolein latex particles conjugated with beta-(3-aminopropyl) 3, 6-dimethylglucopiranoside (DMG), a synthetic analog of PSL = 1 from M. leprae (L-PMG), and its use in the microtitration variant of latex agglutination for the serological diagnosis of lepra. The test was performed in polystyrene plates. A total of 45 blood sera of patients with lepra, 34 sera of subjects who had contacts with leper patients, and 148 control samples were tested. The level of antibodies to DMG was found to be related to the bacterial loading of the patient. If the patients with regressive are seropositive, it means that persistent forms of M.leprae are present in their organs and tissues. "Nonleprous" sera did not react with L-PMG. The microtitration latex agglutination test proved to be highly specific (93.3%) and sufficiently sensitive (87.3%). It is rapid and simple, the results may be assessed visually; this recommends the method for seroepidemiologic screening in the regions where lepra cases are recorded.

Determination of faecal fat by near-infrared spectroscopy

The applicability of near-infrared spectroscopy to determine the amount of fat in faeces has been investigated. Near-infrared spectroscopy was favourably compared with the well known titrimetric method (Van de Kamer et al., J Biol Chem 1948; 177:347-55). A good correlation between near-infrared spectroscopy and the titrimetric method was found. The measurement of faecal fat by near-infrared spectroscopy is found to be more precise than the manual method. Moreover, near-infrared spectroscopy is shown to be a very simple and rapid method for measuring fat in faeces. However, it was shown that performing one's own calibration curve is necessary. Due to this necessity and the costs of the apparatus application of near-infrared spectroscopy is especially advantageous in laboratories with a substantial amount of samples to be analysed.

New in vitro fluorimetric microtitration assays for toxicological screening of drugs

Flow cytometry has been widely used to quantify fluorescent probes in cell culture. However, FCM is not adapted to toxicological screenings due to the cost, the length and the poor reproducibility of this technique. Moreover, several multicenter studies have preferred microtitration methodologies for drug screening. A new fluorimetric technology has been designed that is sensitive and adapted to direct screening in 96-well microplates. This fluorimeter uses cold light technology (CLF) with chemical and physical modifications of the lighting system (Rat et al., 1995). CLF allows reading of UV, visible and near infrared fluorescence by increasing light energy (from 1000 to 2300 lumens) and reducing the calorific part of light (IR > 900 nm, Joule effect). It induces a decrease in background and a 500- to 1000-fold improvement of detection limit of probes in comparison with classical fluorimeters and permits detection of pg/ml to fg/ml. CLF allows easy evaluation of cell injury induced by physical agents (UVA) or chemical toxins (CCl4). Four biological endpoints for cytotoxicity evaluation have been tested with several probes: proliferation (H33258); viability (fluorescent Neutral Red); cell-cell adhesion (calcein-AM); and mitochondrial metabolic effects (Rhodamine 123). Rh123 assay appeared more sensitive than fluorimetric or photometric detection of Neutral Red assay. Cold light fluorimetry (CLF) permits direct detection of low concentrations of probes (pg/ml to fg/ml). CLF is shown to improve classical cytotoxicity assays and, owing to its adaptability to microtitration (in 6-, 12- or 96-well plates and in Petri dishes), it is thus a promising alternative to flow cytometry for drug cytotoxicity screening.

A microtiter plate assay for determining apolipoprotein E genotype and discovery of a rare allele

Genotype determination using the solid-phase minisequencing method of Syvänen et al. (1990, 1993) has been adapted for use with fluorescein-labeled dideoxynucleotides (F-ddNTPs). PCR is performed using one biotinylated primer and one unbiotinylated primer. The biotinylated products are captured in streptavidin-coated microtiter wells. Following removal of nonbiotinylated strands with NaOH, the bound strands are hybridized with a primer adjacent to the polymorphic site being tested. Using T7 DNA polymerase, the primer is extended using one F-ddNTP in the presence of the other three unlabeled ddNTPs. Incorporation of the F-ddNTP is detected by binding antifluorescein antibody conjugated with alkaline phosphatase followed by incubation with a chromogenic substrate. This assay was used to determine APOE genotypes for 75 subjects. The APOE genotypes were also determined using a method involving the incorporation of mobility-shifting nucleotide analogs (Livak et al., 1992). Investigation of the one discrepancy between the two methods revealed that one subject carries a rare APOE allele that has a 3 bp deletion.

Simple assay system for detecting human T cell leukemia virus type I-binding cells and its application in titrating binding inhibitory antibodies

BACKGROUND

A simple and rapid assay system for the detection of human T cell leukemia virus type I (HTLV-I) binding cells was developed to assess the virus specific receptor and titrate the antibodies to block the virus binding.

EXPERIMENTAL DESIGN

Cells (5 x 10(5)) were incubated with 100 microliters of the concentrated HTLV-I at 37 degrees C for 1 hour. After washing, the cells were reacted with anti-HTLV-I envelope monoclonal antibody (rat) for 30 minutes on ice and then stained with fluorescein-isothiocyanate-conjugated anti-rat immunoglobulin. The stained samples were analyzed on FACScan. Antibody-titration of the virus-binding inhibition was carried out by pretreatment of the virus with serially diluted sera.

RESULTS

The specificity of the virus-binding was shown by dose-response relationship, kinetics of the binding, and temperature dependency. HTLV-I was absorbed onto a wide range of human cell lines and peripheral blood lymphocytes at various levels. Antibodies to inhibit the virus-binding were also quantitatively detected in sera from HTLV-I infected individuals, including asymptomatic carriers and patients with adult T cell leukemia or HTLV-I-associated myelopathy, but not from healthy seronegative controls.

CONCLUSIONS

This assay system would be useful in screening the virus-specific receptor and the neutralizing antibodies to HTLV-I. Thus, the assay could be applied to further studies on HTLV-I-related diseases.

Kinetic silver staining and quantification of proteins adsorbed to microtiter plates

A silver stain was used to detect and quantitate proteins adsorbed to microtiter plate wells. The kinetics of the development of the silver stain were analyzed with an automated microtiter plate reader. The lag time for stain development was found to be a consistent indicator of the amount of protein adsorbed to a microtiter plate well. Protein which was not preadsorbed to the microtiter plate was not effectively stained by silver. Complete adsorption of protein applied to the microtiter plate was possible by drying small amounts of protein in very dilute buffers. Variations in sensitivity for different proteins were less than 30% for the panel of proteins examined. Determinations from kinetic silver staining agreed with those from copper staining for bovine albumin adsorbed to microtiter plates. The precision of kinetic silver staining assay was optimal in the range of 40 to 200 ng per microtiter plate well. In this range, the standard deviations averaged less than 5%. Even smaller amounts of protein can be detected and interpolated down to approximately 10 ng per well. The kinetic silver staining method can be used on standard microtiter plate readers without special filters and is readily adaptable to automated systems.

New method for discriminating between calcium stone formers and healthy individuals

A new method for discriminating between the urine of potential calcium stone formers and healthy persons has been proposed, based on determination of the calcium binding capacity of urine (CBC) by titration of early morning urine with a calcium chloride solution. For this purpose a new PVC matrix calcium ion selectrode for measuring calcium ion concentration in whole urine was used. The selectrode has a disposable membrane which can easily be prepared and replaced in the laboratory. Plots of the calcium ion concentration versus the concentration of total added calcium were linear up to a point where precipitation of calcium salts commenced. The slopes of these titration lines were used as criteria for discrimination. Statistical evaluation showed good separation between the urine of healthy and stone forming donors. A 2-sample t test with unequal variances gave mean values of 0.31 for healthy urine (13 samples) and 0.64 for stone forming urine (26 samples). Individual 99% confidence intervals were 0.21-0.40 for the controls and 0.54-0.73 for the patients respectively. Discriminant analysis showed that from a group of treated patients with low Dl (13 samples), 3 were classified as stone formers and 10 were non-formers. Thus there was good correlation with the clinical situation and with the previously proposed Dl test.

Accuracy of the endpoint assay for virus titration

The statistics of estimators used with the endpoint assay for virus titration were investigated. For a standard assay with 10 wells/dilution, the graphical estimator traditionally used was found to produce estimates with significant positive bias and a relatively low accuracy. Furthermore, the graphical estimator was found to be inconsistent. A superior estimator based on the maximum likelihood principle was developed. The results are discussed in relation to the choice between the endpoint titration assay and the plaque assay, and an alternative two-stage assay is presented.

Colorimetric and titrimetric assay of isoniazid

Two methods are proposed for the determination of isoniazid in pure form or in tablets. In the first method chlorpromazine hydrochloride, when treated with 2-iodoxybenzoic acid as an oxidant in 50% w/v o-phosphoric acid solution, is oxidized to chlorpromazine free radical which absorbs at 530 nm. The red free radical is readily reduced quantitatively by isoniazid to the colourless chloropromazine. The addition of isoniazid to a red solution of chlorpromazine free radical results in a decrease in absorbance in direct proportion to the quantity of isoniazid. This forms the basis for the quantitative determination of micro-quantities of isoniazid (3-18 micrograms ml-1). The second method involves the titrimetric determination of isoniazid using N-bromophthalimide as a titrant. The end-point is determined either directly using methyl red or amaranth as indicator, or by a back titration method in which a known excess of N-bromophthalimide solution is added to isoniazid solution and then the residual unreacted reagent is determined iodometrically. The results by the proposed procedures were in good agreement with those obtained by the official methods.

Analysis of the buffering systems in dental plaque

A semi-micro method was used for investigation of the buffering properties of whole plaque, plaque fluid, and washed plaque bacteria. Artifacts associated with titration of samples containing live bacteria were noted and their effects estimated. All three sample types showed minimal buffering in the region of neutrality, with much stronger buffering in the regions pH 4-5.5 and pH 8-9. For the range pH 4-7, almost 90% of the total buffer capacity of plaque appeared to be accounted for by macromolecules of bacterial cell walls and plaque matrix. Extracellular buffers in plaque fluid removable by centrifugation contributed up to 11%. These buffers (probably soluble proteins, peptides, organic acids, and phosphate) are, potentially at least, capable of exchange with saliva. In vitro, bicarbonate (dissolved in the extracellular fluid) contributed only 2-5% of total buffering; there was no evidence of formation of carbamino compounds. However, in vivo, salivary bicarbonate may be important as a continually replenished source of additional buffering.