Searching for Hidden Neutrons with a Reactor Neutrino Experiment: Constraints from the STEREO Experiment

Different extensions of the standard model of particle physics, such as braneworld or mirror matter models, predict the existence of a neutron sterile state, possibly as a dark matter candidate. This Letter reports a new experimental constraint on the probability p for neutron conversion into a hidden neutron, set by the STEREO experiment at the high flux reactor of the Institut Laue-Langevin. The limit is p<3.1×10^{-11} at 95% C.L. improving the previous limit by a factor of 13. This result demonstrates that short-baseline neutrino experiments can be used as competitive passing-through-walls neutron experiments to search for hidden neutrons.

Biorefinery potential of sustainable municipal wastewater treatment using fast-growing willow

The use of willow plantations can be a sustainable approach for treating primary municipal wastewater, potentially reducing both the environmental and economic burdens associated with conventional treatment. However, the impact of wastewater irrigation upon the willow biorefinery potential has not yet been established. To investigate this effect, three-year-old field grown willows were harvested from plots kept as either controls or irrigated with primary municipal wastewater effluent at 29.5 million L ha^-1 yr^-1. Biomass compositional analysis, ionic liquid pretreatment and enzymatic saccharification were assessed and differential abundance of persistent extractable phytochemicals was evaluated using untargeted metabolite profiling. Glucan significantly increased by 8% in wastewater treated trees, arabinose and galactose were significantly decreased by 8 and 29%, respectively, while xylose, mannose and lignin content were unaltered. Ionic liquid pretreatment and enzymatic saccharification efficiencies did not vary significantly, releasing >95% of the cell wall glucose and recovering 35% of the lignin. From a total of 213 phytochemical features, 83 were significantly depleted and 14 were significantly enriched due to wastewater irrigation, including flavonoids and lignan derivatives. Considered alongside increased biomass yield from wastewater irrigation (+200%), lignocellulosic bioenergy yields increased to 8.87 t glucose ha^-1 yr^-1 and 1.89 t ha^-1 yr^-1 recovered lignin, while net extractives yields increased to 1.48 t ha^-1 yr^-1, including phytochemicals of interest. The maintenance of glucose accessibility after low-cost ionic liquid pretreatment is promising evidence that sustainable lignocellulose bioenergy production can complement wastewater treatment. Untargeted metabolite assessment revealed some of the phytochemical toolkit employed by wastewater irrigated willows, including accumulation of flooding and salinity tolerance associated flavonoids glabraoside A and glabrene. The extractable phytochemicals underpin a novel high biomass phenotype in willow and, alongside lignocellulosic yields, could help enhance the economic feasibility of this clean wastewater treatment biotechnology through integration with sustainable biorefinery.

Wine-on-tap: A study on the conservation of wines in keg Ecofass®

As more and more consumers around the world integrate the choice of healthier, more ethical and eco-friendlier food and beverages in their lifestyle, the wine industry is pushed to develop more sustainable production, distribution and consumption solutions. In search of wine preservation improvements that would have both economic and ecological positive impacts, the wine industry has been investing resources in research, development and innovation regarding alternative packaging and distribution solutions for years. The keg Ecofass® is made of recyclable plastic material, high density polyethylene (HDPE) in which there is an aluminium pouch containing the liquid food. It was a question of knowing if this type of container was adapted to the conservation of the wines during several months. The method of storage and distribution has also been studied to know the impact on the oenological and sensory quality of the wines. Likewise, the nature of the pressure gas (nitrogen or compressed air) has also been tested. The contents of free and total SO2 and CO2 were monitored, and sensory analysis tests were carried out. Nevertheless, at the sensory level, the judges were able to note significant differences between the wines.

Assessment of a 2,4,6-trinitrotoluene-contaminated site using Aporrectodea rosea and Eisenia andrei in mesocosms

Polynitro-organic compounds such as 2,4,6-trinitrotoluene (TNT) can be released into the environment from production and processing facilities and military firing ranges as well as through field use and disposal practices. Based on laboratory toxicity data, TNT has lethal (at >/=260 mg TNT/kg dry soil) and sublethal effects (at >/=59 mg TNT/kg dry soil) to the earthworm. However, field studies are needed to relate exposure of organisms to explosives in mixed-contaminated soil under field conditions and to define effects-based ecotoxicologic benchmarks for TNT-contaminated soil. In the present study, the lethal and sublethal effects of a 10-day in situ exposure at a TNT-contaminated field site using mesh-bag mesocosms were assessed. In addition to the survival end point, the biomarkers of earthworm exposure and effect-including tissue residues, lysosomal neutral red retention time (NRRT), and total immune activity (TIA)-were measured. Concentrations of TNT in soil mesocosms ranged from 25 to 17,063 mg/kg. Experiments indicated a trend toward decreasing survival of caged Aporrectodea rosea and Eisenia andrei as the concentration of TNT and total nitroaromatic compounds increased. E. andrei tolerated higher concentrations of TNT (up to 4050 mg/kg dry soil) in mesocosms than did indigenous earthworms, who survived only at </=1146 mg TNT/kg. Earthworms E. andrei and A. rose survived in 67% and 75% of TNT-contaminated mesocosms, respectively, compared with references groups. NRRT was significantly decreased in surviving earthworms from the contaminated areas compared with those from the reference site. TIA was not affected by field exposure to TNT. Earthworm tissue concentrations of TNT metabolites 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene were not correlated with TNT soil concentrations. In addition, higher tissue concentrations of TNT metabolites were observed at concentrations ranging from 116 to 130 mg TNT/kg soil. The results showed that earthworm exposure in TNT-contaminated soil produced both lethal and sublethal effects in the field. The results of study indicated that mesocosm experiments would be useful to assess the toxicity of a site and to characterize the overall effects of contaminants. However, mesocosm experiments present special considerations (e.g., abiotic factors, exposure period) when used at heterogenous sites, and data must be interpreted with caution.

In vitro effect of cryptophycin 52 on microtubule assembly and tubulin: molecular modeling of the mechanism of action of a new antimitotic drug

Cryptophycin 52 (C52) is a new synthetic compound of the cryptophycin family of antitumor agents that is currently undergoing clinical evaluation for cancer chemotherapy. The cryptophycin class of compounds acts on microtubules. This report details the mechanism by which C52 substoichiometrically inhibits tubulin self-assembly into microtubules. The inhibition data were analyzed through a model described by Perez-Ramirez [Perez-Ramirez, B., Andreu, J. M., Gorbunoff, M. J., and Timasheff, S. N. (1996) Biochemistry 35, 3277-3285]. We thereby determined the values of the apparent binding constant of the tubulin-C52 complex to the end of a growing microtubule (K(i)) and the apparent binding constant of C52 to tubulin (K(b)). The binding of C52 depended on tubulin concentration, and binding induced changes in the sedimentation pattern of tubulin, which indicates that C52 induces the self-association of tubulin and tubulin aggregates other than microtubules. Using analytical ultracentrifugation and electron microscopy, we show that C52 induces tubulin to form ring-shaped oligomers (single rings). We also show that C52 inhibits the formation of double rings from either GTP- or GDP-tubulin. In addition, the advances made by electron crystallography in understanding the structure of the tubulin and the microtubule allowed us to visualize the putative binding site of C52 and to reconstruct C52-induced ring oligomers by molecular modeling.

Asymmetrical properties of the optical reflection response of the Fabry-Pérot interferometer

It may be shown that, even when a Fabry-Pérot interferometer is used with plane waves propagating at normal incidence, the variations of the intensity reflected by it with respect to the phase difference (induced by the distance between the two mirrors) are generally not symmetrical around its extrema. We study this problem and express the necessary and general conditions for obtaining a symmetrical optical response in the reflection mode. We analyze the simple case of a Fabry-Pérot interferometer the first mirror of which is constituted by a thin layer of metal.

Ecotoxicological characterization of energetic substances using a soil extraction procedure

The acetonitrile-sonication extraction method (US EPA SW-846 Method 8330) and aquatic-based toxicity tests were used on laboratory and field samples, to characterize the ecotoxicity of soils contaminated with energetic substances. Spiked soil studies indicated that 2,4, 6-trinitrotoluene (TNT)-dependent soil toxicity could be measured in organic extracts and aqueous leachates using the 15-min Microtox (Vibrio fischeri, IC50=0.27 to 0.94 mg TNT/liter incubation medium) and 96-h Selenastrum capricornutum growth inhibition (IC50=0.62 to 1. 14 mg/liter) toxicity tests. Analyses of leachates of composite soil samples [containing TNT and some TNT metabolites, 1,3,5-trinitro-1,3, 5-triazacyclohexane (RDX), and 1,3,5,7-tetranitro-1,3,5, 7-tetrazacyclooctane (HMX)] from an explosives manufacturing facility, indicated toxicities similar to those found in the TNT-spiked soil studies and pure TNT in solution, and suggested that TNT was the major toxicant. Using TNT as a model toxicant in soils having different moisture contents (20% vs dry) and textures (sandy vs clayey-sandy) but similar organic matter content (3-4%), multi-factorial analyses of Microtox test data revealed that these soil factors significantly influenced the TNT extractability from soil and subsequent toxicity measurements. Taken together, data indicate that the modified Method 8330 may be used in conjunction with ecotoxicity tests to reflect the toxic potential of soils contaminated with energetic substances.

Differentiation of human colon cancer cells changes the expression of beta-tubulin isotypes and MAPs

The human colon adenocarcinoma HT29-D4 cell line is an interesting model for studies on epithelial cell differentiation. Undifferentiated cells are malignant proliferating cells, whereas differentiated cells act like epithelial polarized cells. In the present study, we first characterized the action of taxoids on the microtubular network of HT29-D4 cells according to the state of differentiation. Microtubular bundles were found in undifferentiated cells but not in differentiated cells, even with 500-fold higher taxoid concentrations for 96 h. This finding led us to study changes in microtubules according to the polarity status of the cell. E-MAP-115 was expressed only in differentiated cells; expression of beta-tubulin isotypes was altered in them relative to undifferentiated cells. Classes I, II, III, IVa and IVb isotypes were expressed in both phenotypes; however, differentiated epithelial cells displayed a specific increase in class III beta-tubulin. Thus, the increase in expression of this beta-tubulin isotype in differentiated cells is not restricted to neuronal cells. Moreover, these expression changes may reflect a higher stability of microtubular network in differentiated cells, which may explain the lower activity of anti-microtubule agents, independently of the mitotic process. These results indicate that the composition of microtubules should be considered as one of the criteria involved in the response of tumour cells to chemotherapy with anti-microtubule agents.

Development of a soil extraction procedure for ecotoxicity characterization of energetic compounds

The acetonitrile-sonication extraction method (US EPA Method 8330) associated with aquatic-based toxicity tests was examined to study the ecotoxicity of energetic substances in soil. Three studies were carried out: (1) toxicological characterization of different energetic substances to select a representative toxicant and to validate the choice of bioassays; (2) choice of an appropriate solvent to transfer acetonitrile extracts to the bioassay incubation media; and (3) optimization of Method 8330 using soil samples spiked with the toxicant. Initial studies indicated that pure 2,4,6-trinitrotoluene (TNT) was toxic to Vibrio fischeri [Microtox; IC50 (15 min) of 4.2 microM], whereas RDX was less toxic (IC20 = 181 microM) and HMX was not toxic up to its limit of water solubility (< 22 microM). Selected pure TNT metabolites were less toxic than TNT. Similar results were found using the 96-h Selenastrum capricornutum growth inhibition test. The toxicity of pure TNT in different solvents (acetonitrile, acetone, and DMSO) and that from Method 8330-extracted TNT-spiked soil samples were compared to TNT dissolved in water. Data indicated that DMSO was the most appropriate solvent to transfer the acetonitrile extracts. A modified Method 8330 may be used in conjunction with bioassays and chemical analyses to examine the ecotoxicity of soils contaminated with energetic substances.

Differential effects of ethyl 5-amino-2-methyl-1,2-dihydro-3-phenylpyrido[3,4-b]pyrazin-7-yl carbamate analogs modified at position C2 on tubulin polymerization, binding, and conformational changes

NSC 613863 (R)-(+) and NSC 613862 (S)-(-) (CI980) are two chiral isomers of ethyl 5-amino 2-methyl-1,2-dihydro-3-phenylpyrido[3,4-b]pyrazin-7-yl carbamate which have potent antitubulin activity. The S-isomer is a more potent antimitotic compound than the R-isomer, and the two isomers differ markedly in binding to tubulin [Leynadier, D., Peyrot, V., Sarrazin, M., Briand, C., Andreu, J. M., Rener, G. A., & Temple, C., Jr. (1993) Biochemistry 32, 10675-10682]. To understand the origin of such differences, we studied the interactions of three R- and S-isomer structural analogs which differ in C2 (the chiral carbon), i.e., C179, NSC 337238, and NSC 330770. C179 is a methylated dehydrogenated achiral compound. It bound to tubulin with an apparent affinity Ka of (2.29 +/- 0.17) x 10(4) M-1, inhibited tubulin polymerization in vitro at a half-inhibitory concentration (IC50) of 100 microM, and presented no GTPase activity. The substitution of -CH3 by -H leads to the NSC 337238 compound. It bound to tubulin with a higher affinity [Ka = (2.62 +/- 0.35) x 10(5) M-1] and inhibited tubulin polymerization at a lower concentration (IC50 = 14 microM). It presented no GTPase activity and induced the formation of abnormal polymers at a protein critical concentration (Cr) of 2 mg mL-1. NSC 330770, a demethylated hydrogenated molecule, interacted strongly with tubulin [Ka = (3.30 +/- 0.56) x 10(6) M-1].(ABSTRACT TRUNCATED AT 250 WORDS)

Chloride dependent intracellular pH increase induced by bepridil in human red blood cells: a possible involvement in correction of ischemic acidosis

Inhibitors of Na+/H+ exchanger are reported to exert an anti-ischemic effect. Some calcium antagonists and particularly bepridil are commonly used as anti-ischemic agents. Therefore, in this study, we test the hypothesis that protective effect against ischemia may occur at least in part through an action on Na+/H+ exchanger. The effect of some calcium antagonists on Na+/H+ exchanger from acid-loaded and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium salt (DIDS)-treated human red cells (RBC) has been studied with a pHstat technique. Doses above those required to affect calcium channel (10(-5) and 10(-4) M) of nifedipine, nicardipine, verapamil and diltiazem had no effect on Na+/H+ exchanger activity. Ethyl isoproply amiloride (10(-4) M) completely inhibited the exchanger. Among the calcium antagonists tested, bepridil exhibited a particular effect, dissipating the pH gradient independently from the Na+/H+ exchanger activity. Bepridil's effect on DIDS-treated RBC was compared with that of a well known protonophore, carbamyl cyanide p-(trifluoromethoxy)phenyl hydrazone, and with that of tributyltin, which mediates a Cl-/OH- exchange across the cell membrane. Bepridil (> 2 x 10(-6) M) acts like tributyltin by dissipating the pH gradient whatever the external cation (Na+ or K+) or the membrane potential, and its action depends on the ratio intracellular [Cl-]/extracellular [Cl-]. The dissipation seems to occur through an OH-/Cl- exchange but other mechanisms may intervene. Moreover, intraerythrocytic pH measurement by 31P nuclear magnetic resonance clearly showed that bepridil permits the cell to recover normal pH faster than control.(ABSTRACT TRUNCATED AT 250 WORDS)

Tubulin binding of two 1-deaza-7,8-dihydropteridines with different biological properties: enantiomers NSC 613862 (S)-(-) and NSC 613863 (R)-(+)

Several fluorescence properties of two enantiomers, NSC 613862 (S)-(-) and NSC 613863 (R)-(+), have been compared. Even though the two isomers showed the same fluorescence behavior in solution in different solvents, drastic differences were observed after binding to purified calf brain tubulin. Binding measurements for the two compounds were performed both by fluorescence spectroscopy and by column gel permeation, a direct method of measurement. For both isomers, the binding was characterized by the presence of one high-affinity binding site with an apparent association constant of (3.2 +/- 0.5) x 10(6) M-1 and (4.1 +/- 0.9) x 10(6) M-1 for the R- and S-isomer, respectively, and by several low-affinity sites. Both isomers were also shown to induce GTPase activity in tubulin. The high-affinity binding site seems to be the same for the two isomers. Moreover, fluorescence competition experiments suggest at least a partial overlap of the colchicine and podophyllotoxin site. To explain the differences in fluorescence behavior after binding to tubulin, we hypothesize that the R-isomer is positioned differently in its binding locus as compared with the S-isomer.

Mechanism of binding of the new antimitotic drug MDL 27048 to the colchicine site of tubulin: equilibrium studies

MDL 27048 [trans-1-(2,5-dimethoxyphenyl)-3-[4-(dimethylamino)phenyl]-2- methyl-2-propen-1-one] fluoresces when bound to tubulin but not in solution. This effect has been investigated and found to be mimicked by viscous solvents. Therefore, MDL 27048 appears to be a fluorescent compound whose intramolecular rotational relaxation varies as a function of microenvironment viscosity. The binding parameters of MDL 27048 to tubulin have been firmly established by fluorescence of the ligand, quenching of the protein fluorescence, and gel equilibrium chromatography. The apparent binding equilibrium constant was (2.75 +/- 0.45) x 10(6)M-1, and the binding site number was 0.81 +/- 0.12 (10 mM sodium phosphate-0.1 mM GTP, pH 7.0, at 25 degrees C). The binding is exothermic. The binding of MDL 27048 overlaps the colchicine and podophyllotoxin binding sites. Binding of MDL 27048 to the colchicine site was also measured by competition with MTC [2-methoxy-5-(2,3,4-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-one] , a well-characterized reversibly binding probe of the colchicine site [Andreu et al. (1984) Biochemistry 23, 1742-1752; Bane et al., (1984) J. Biol. Chem. 259, 7391-7398]. In contrast with close analogues of colchicine, MDL 27048 and podophyllotoxin neither affected the far-ultraviolet circular dichroism spectrum of tubulin, within experimental error, nor induced tubulin GTPase activity. Like podophyllotoxin, an excess of MDL 27048 over tubulin induced no abnormal cooperative polymerization of tubulin, which is characteristic of colchicine binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Conformational change induced by coenzyme binding to bovine liver dihydrofolate reductase: a spectrofluorimetric study

When NADPH was added in excess to a bovine liver DHFR solution, a fluorescence peak due to an energy transfer mechanism was apparent at 450 nm. It did not vary over time. The intrinsic fluorescence peak of DHFR at 320 nm was quenched and this phenomenon increased over the time-course after NADPH addition. This result was ascribed to a slow DHFR conformational change induced by NADPH binding, which has never been previously described in such a long time scale (more than 30 min). A kinetic scheme accounting for this mechanism has been proposed. Furthermore, this interconversion between two protein conformers led to an increase in the initial apparent rate of the enzymatic reaction catalyzed by DHFR.

Kinetic Modeling of Intracellular pH and Comparison with 31P NMR Experimental Values in Dialysed Uremic Patients

Changes in intra-erythrocytic pH values over time, during and after bicarbonate hemodialysis, were studied with 31P Nuclear Magnetic Resonance. Simultaneously, pH values of whole blood were obtained by a gazometric method. A two-compartment model appeared to be the simplest kinetic model to explain the shifts in proton concentrations in extra- and intracellular media. Non-linear regression was used to determine exchange constant values. There was a very good correlation between the experimental and calculated proton concentrations. This model can describe all patients but individual experimental constants must be determined. Under these conditions a single blood pH determination before dialysis will permit determination of the initial intra-erythrocytic pH and monitoring of intra-erythrocytic pH during hemodialysis.

Kinetic modeling of intracellular pH and comparison with 31P NMR experimental values in dialysed uremic patients

Changes in intra-erythrocytic pH values over time, during and after bicarbonate hemodialysis, were studied with 31P Nuclear Magnetic Resonance. Simultaneously, pH values of whole blood were obtained by a gazometric method. A two-compartment model appeared to be the simplest kinetic model to explain the shifts in proton concentrations in extra- and intra-cellular media. Non-linear regression was used to determine exchange constant values. There was a very good correlation between the experimental and calculated proton concentrations. This model can describe all patients but individual experimental constants must be determined. Under these conditions a single blood pH determination before dialysis will permit determination of the initial intra-erythrocytic pH and monitoring of intra-erythrocytic pH during hemodialysis.

Interaction of tubulin and cellular microtubules with the new antitumor drug MDL 27048. A powerful and reversible microtubule inhibitor

We have characterized the binding of trans-1-(2,5-dimethoxyphenyl)-3-[4-(dimethylamino)phenyl]-2-methyl-2- propen- 1-one (MDL 27048) to purified procine brain tubulin, and the inhibition of microtubule assembly by this compound in vitro and using cultured cells. Binding measurements were performed by difference absorption and fluorescence spectroscopy. MDL 27048 binds to one site/tubulin heterodimer with an apparent equilibrium constant Kb = (2.8 +/- 0.8) X 10(6) M-1 (50 mM 2-(N-morpholino)ethanesulfonic acid, 1 mM [ethylenebis(oxyethylenenitrilo)]tetraacetic acid, 0.5 mM MgCl2, 0.1 mM GTP buffer, pH 6.7, at 25 degrees C). Podophyllotoxin displaced the binding of MDL 27048, suggesting an overlap with the colchicine-binding site. Assembly of purified tubulin into microtubules was inhibited by substoichiometric concentrations of MDL 27048, which also induced a slow depolymerization of preassembled microtubules. The cytoplasmic microtubules of PtK2 cells were disrupted in a concentration and time-dependent manner by MDL 27048, as observed by indirect immunofluorescence microscopy. Maximal depolymerization took place with 2 X 10(-6) M MDL 27048 in 3 h. When the inhibitor was washed off from the cells, fast microtubule assembly (approximately 8 min) and complete reorganization of the cytoplasmic microtubule network (15-30 min) were observed. MDL 27048 also induced mitotic arrest in SV40-3T3 cell cultures. Due to all these properties, this anti-tumor drug constitutes a new and potent microtubule inhibitor, characterized by its specificity and reversibility.

Influence of time and chloride ions on the interaction of cisplatin with human albumin in-vitro

The interaction of cis-dichlorodiammineplatinum (II) (cisplatin) with human serum albumin (HSA), dissolved in phosphate buffer with or without sodium chloride (0.1 M) has been examined at pH 7.4 and mu = 0.154. Equal volumes of cisplatin and HSA solutions were incubated at 37 degrees C for various times and filterable platinum concentrations versus time measured by flameless atomic absorption spectrophotometry. Binding kinetics differed depending on the buffer solutions used and on the time elapsing between cisplatin dissolution and outset of incubation with HSA. Experimental data were fitted to a theoretical equation used to calculate the number of nucleophilic sites per HSA molecule. Titrations of the HSA sulphydryl group content before and after incubation with a cisplatin solution were made, from which it was shown that the lone SH-group of the HSA macromolecule is involved in cisplatin binding. We also studied HSA's sensitivity towards denaturing agents when it was complexed with cisplatin. This sensitivity was decreased upon cisplatin binding. Also, the binding capacities of HSA and the HSA-Pt(II) complex to both tryptophan and warfarin were compared to determine the possible influence of cisplatin upon the binding to HSA of other drugs; this influence was negligible.

In vitro plasma binding of some second generation antitumor platinum complexes

The kinetics of five cisplatin analogs binding to human plasma fractions possessing a molecular weight greater than 50,000 daltons were studied. Each drug solution in plasma ultrafiltrate or phosphate buffer (pH = 7.4, mu = 0.154) was mixed with human plasma and filterable platinum concentrations were measured versus time by atomic absorption spectrophotometry. The only Pt IV compound studied did not bind. All the other Pt II complexes bound, but their binding kinetics were quite different. The experimental data were fitted to a theoretical equation based on the hypothesis that plasma nucleophilic agents possessing a molecular weight greater than 50,000 daltons are able to react with Pt compounds with an apparent second order rate constant. The apparent reaction rate constants and initial concentrations of these nucleophilic agents were calculated. The difference between the respective values obtained for each cisplatin analog could be explained by differences in their chemical formulas. Therefore our result should contribute towards a better understanding of the pharmacokinetics of the cisplatin analogs studied.

Fluorescence study of human beta 2 microglobulin

A fluorescence study human beta 2 microglobulin showed the existence of two types of Trp residues, one quite exposed to the solvent, the other buried in a hydrophobic environment. The change in excitation wavelength made obvious the existence of a Tyr to Trp energy transfer mechanism. Treatment by urea or guanidine chlorhydrate brought about quite different results. With the former denaturing agent, some Trp residues remained buried; with the latter, the protein was completely unfolded, as proved by iodide quenching. pH variations could not unfold beta 2m enough to convert all Trp residues to exposed ones. When heated, beta 2m supported a transition that began at 50 degrees (melting temperature 63 degrees) and was not reversible. All these results suggest a rather compact conformation as in a globular protein.

Study of the interaction between human serum albumin and some cephalosporins

Dialysis and microcalorimetric methods were used to calculate the binding parameters of some cephalosporins to human serum albumin (HSA) and to study the nature of the interactions involved in the binding process. Dialysis results agree with microcalorimetric data for cephapirin, cephradin, cefamandole, and cefazolin. Binding forces seem to be principally electrostatic. The parts of the drug molecule involved in HSA drug binding have been identified by high-resolution NMR. The major binding site for cephalosporins with high HSA affinity is thought to be the electron-rich heterocyle fixed on the methylene at position 3. Four classes of cephalosporin have been defined: (a) very weak affinity for HSA (cephalexin, cephradin); (b) moderate affinity (cephapirin, cefoxitin, and cefotaxime) in which binding to the protein involves the heterocycle substituent of the acetamide chain carbon atom; (c) strongly binding (cefamandole), in which binding to HSA is by means of the methyltetrazole ring; and, finally (d), cefazolin, with two classes of binding sites for protein, showing strong and moderate affinity.