Effect Of Protein Denaturation Research Articles

Localization of porphyrins and their metal complexes in albumin and its effect on protein aggregation and denaturation

Albumin is a globular protein with a number of functions of vital importance. Its aggregation can cause serious problems and cause hypoalbuminemia. Albumin complex formation with endogenous and exogenous porphyrins can lead to aggregation. This work is a study of the localization effect of a number of endogenous porphyrins, such as protoporphyrin, hematoporphyrin, deuteroporphyrin and their metal complexes in an albumin globule on the albumin state in solutions and resistance of protein complexes to thermally induced denaturation. The structure of the obtained complexes was determined by the IR and fluorescence spectroscopy methods in combination with molecular docking. The results obtained show that nature porphyrins form hydrogen bonds with various sections of the albumin polypeptide chain and cause changes in the protein secondary structure associated with the transformation of α-helices into β-folds and subsequent protein aggregation. The DSC studies revealed that complex formation with porphyrins lowered the thermal effect of protein denaturation by 50–67%. The dependence of the structure of the complexes on the denaturation thermal effect was analyzed. It was established that the changes in the protein denaturation thermal effect could be used to determine porphyrin localization in the protein globule and protein ability to form aggregates, following complex formation.

Disinfection efficacy and mechanism of olanexidine gluconate against norovirus

BackgroundThe purpose of this study was to evaluate the virucidal activity of a new olanexidine-containing formulation for hand hygiene (olanexidine gluconate hand rub; OLG-HR) against non-enveloped viruses and to understand its mechanism of action. MethodsThe virucidal activities of OLG-HR against two strains of caliciviruses and three adenovirus serotypes were evaluated through suspension tests. Also, virus-like particles were used to predict the effect of olanexidine gluconate on virus particle structure. ResultsThe results of suspension tests under conditions with and without interfering substances (1.5% BSA) indicated that OLG-HR had a broad-spectrum effect against non-enveloped viruses, and the virucidal effect was unaffected by organic contaminants. Furthermore, olanexidine inhibited the binding ability of virus-like particles to the binding receptor of human norovirus and increased the aggregation of virus-like particles in a dose-dependent manner. Transmission electron microscopy showed that the morphology of the virus-like particles was affected by exposure to olanexidine, indicating that the protein-denaturing effect of olanexidine gluconate caused the loss of receptor-binding capability of the viral capsid protein. ConclusionsThis study suggests that olanexidine gluconate is a potential biological and environmental disinfectant against norovirus and adenovirus.

Effect of protein denaturation and lipid removal on rice physicochemical properties

The physicochemical properties of rice are influenced by their chemical components and their interactions. It has been demonstrated that the interactions among rice chemical components are enhanced by protein denaturation (PD) via heat treatment and by lipid removal (LR) via solvent extraction. The objective of this study was to investigate the impacts of PD, LR, and their combined treatments on the gelatinization and pasting properties, swelling power, and water solubility of four brown rice flours. Rice protein was denatured under a vacuum at 100 °C, and rice lipid was removed via hexane for varying times. The combined treatments were done in two ways, PD followed by LR (PD-LR), and LR followed by PD (LR-PD). The results showed that PD increased gelatinization temperatures, while LR decreased gelatinization temperatures. Both PD and LR reduced pasting and swelling properties; however, PD resulted in a greater decrease than LR. Polar lipids are proposed to serve as bridges to link denatured proteins and starch granules in the combined treatments, resulting in greater decreases in the pasting and swelling properties than the individual treatments. The results obtained in this study demonstrate the importance of starch-lipid-protein interactions on the physicochemical properties of brown rice flour.

Rheological Characterization of a Wood Adhesive Based on a Hydrolyzed Soy Protein Suspension

Soy protein (SP) is a promising raw material for the development of renewable and environmentally friendly adhesives. This work aims to study the effect of protein denaturation and/or hydrolysis on the rheology of a soy protein isolate (SPI) suspension. Four stages of chemical modification of SPI were evaluated: unmodified (U), denatured (D), partially hydrolyzed (PH) and fully hydrolyzed (H). Fourier-transform infrared spectroscopy (FTIR) and sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) confirmed that polypeptides with high molecular weight were fully fragmented into smaller ones. Rheological analysis showed that U behaves as a gel-like material while PH and H act as viscous-like materials. Hydrolysis caused a significant decrease in the viscosity, even for suspensions with high solid content. Furthermore, comparing U and H, the viscosity at high shear strength dropped 65% with an increase of 219% in the solid content. The shear strength of the adhesives can be increased through two strategies: crosslinking with epoxy resin and the addition of different reinforcements. Considering suspension H as reference, the addition of 20% epoxy resin and 5% montmorillonite clay caused an increase in the shear strength of almost 39%. These results could contribute to the development of high solid content SP-based adhesive with desirable rheological properties and zero formaldehyde emission.

Effect of Protein Denaturation and Enzyme Inhibitors on Proteasomal-Mediated Production of Peptides in Human Embryonic Kidney Cells.

Peptides produced by the proteasome have been proposed to function as signaling molecules that regulate a number of biological processes. In the current study, we used quantitative peptidomics to test whether conditions that affect protein stability, synthesis, or turnover cause changes in the levels of peptides in Human Embryonic Kidney 293T (HEK293T) cells. Mild heat shock (42 °C for 1 h) or treatment with the deubiquitinase inhibitor b-AP15 led to higher levels of ubiquitinated proteins but did not significantly increase the levels of intracellular peptides. Treatment with cycloheximide, an inhibitor of protein translation, did not substantially alter the levels of intracellular peptides identified herein. Cells treated with a combination of epoxomicin and bortezomib showed large increases in the levels of most peptides, relative to the levels in cells treated with either compound alone. Taken together with previous studies, these results support a mechanism in which the proteasome cleaves proteins into peptides that are readily detected in our assays (i.e., 6–37 amino acids) and then further degrades many of these peptides into smaller fragments.

Effects of high pressure freezing (HPF) on denaturation of natural actomyosin extracted from prawn (Metapenaeus ensis).

Effects of protein denaturation caused by high pressure freezing, involving Pressure-Factors (pressure, time) and Freezing-Factors (temperature, phase transition, recrystallization, ice crystal types), are complicated. In the current study, the conformation and functional changes of natural actomyosin (NAM) under pressure assisted freezing (PAF, 100,150,300,400,500MPaP-20°C/25min), pressure shift freezing (PSF, 200MPaP-20°C/25min), and immersion freezing (0.1MPaP-20°C/5min) after pressure was released to 0.1MPa, as compared to normal immersion freezing process (IF, 0.1MPaP-20°C/30min). Results indicated that PSF (200MPaP-20°C/30min) could reduce the denaturation of frozen NAM and a pressure of 300MPa was the critical point to induce such a denaturation. During the periods of B→D in PSF or B→C→D in PAF, the generation and growth of ice crystals played an important role on changing the secondary and tertiary structure of the treated NAM.

Spin-Dependent Transport through Chiral Molecules Studied by Spin-Dependent Electrochemistry

ConspectusMolecular spintronics (spin + electronics), which aims to exploit both the spin degree of freedom and the electron charge in molecular devices, has recently received massive attention. Our recent experiments on molecular spintronics employ chiral molecules which have the unexpected property of acting as spin filters, by way of an effect we call “chiral-induced spin selectivity” (CISS). In this Account, we discuss new types of spin-dependent electrochemistry measurements and their use to probe the spin-dependent charge transport properties of nonmagnetic chiral conductive polymers and biomolecules, such as oligopeptides, L/D cysteine, cytochrome c, bacteriorhodopsin (bR), and oligopeptide-CdSe nanoparticles (NPs) hybrid structures. Spin-dependent electrochemical measurements were carried out by employing ferromagnetic electrodes modified with chiral molecules used as the working electrode. Redox probes were used either in solution or when directly attached to the ferromagnetic electrodes. During the electrochemical measurements, the ferromagnetic electrode was magnetized either with its magnetic moment pointing “UP” or “DOWN” using a permanent magnet (H = 0.5 T), placed underneath the chemically modified ferromagnetic electrodes. The spin polarization of the current was found to be in the range of 5–30%, even in the case of small chiral molecules. Chiral films of the l- and d-cysteine tethered with a redox-active dye, toludin blue O, show spin polarizarion that depends on the chirality. Because the nickel electrodes are susceptible to corrosion, we explored the effect of coating them with a thin gold overlayer. The effect of the gold layer on the spin polarization of the electrons ejected from the electrode was investigated. In addition, the role of the structure of the protein on the spin selective transport was also studied as a function of bias voltage and the effect of protein denaturation was revealed. In addition to “dark” measurements, we also describe photoelectrochemical measurements in which light is used to affect the spin selective electron transport through the chiral molecules. We describe how the excitation of a chromophore (such as CdSe nanoparticles), which is attached to a chiral working electrode, can flip the preferred spin orientation of the photocurrent, when measured under the identical conditions. Thus, chirality-induced spin polarization, when combined with light and magnetic field effects, opens new avenues for the study of the spin transport properties of chiral molecules and biomolecules and for creating new types of spintronic devices in which light and molecular chirality provide new functions and properties.

Cu/Zn-superoxide dismutase and glutathione are involved in response to oxidative stress induced by protein denaturing effect of alachlor in Saccharomyces cerevisiae

Alachlor is a widely used pre-emergent chloroacetanilide herbicide which has been shown to have many harmful ecological and environmental effects. However, the mechanism of alachlor-induced oxidative stress is poorly understood. We found that, in Saccharomyces cerevisiae, the intracellular levels of reactive oxygen species (ROS) including superoxide anions were increased only after long-term exposure to alachlor, suggesting that alachlor is not a pro-oxidant. It is likely that alachlor-induced oxidative stress may result from protein denaturation because alachlor rapidly induced an increased protein aggregation, leading to upregulation of SSA4 and HSP82 genes encoding heat shock proteins (Hsp) of Hsp70 and Hsp90 family, respectively. Although only SOD1 encoding Cu/Zn-superoxide dismutase (SOD), but not SOD2 encoding Mn-SOD, is essential for alachlor tolerance, both SODs play a crucial role in reducing alachlor-induced ROS. We found that, after alachlor exposure, glutathione production was inhibited while its utilization was increased, suggesting the role of glutathione in protecting cells against alachlor, which becomes more important when lacking Cu/Zn-SOD. Based on our results, it seems that alachlor primarily causes damages to cellular macromolecules such as proteins, leading to an induction of endogenous oxidative stress, of which intracellular antioxidant defense systems are required for elimination.

Stabilizing effects of excipients on dissociation of intact (146S) foot-and-mouth disease virions into 12S particles during storage as oil-emulsion vaccine

Most conventional foot-and-mouth disease virus (FMDV) vaccines contain oil-adjuvant. Their potency decreases upon prolonged storage. Intact (146S) FMDV particles can dissociate into 12S degradation products with a concomitant decrease in immunogenicity. We therefore measured virion stability in vaccines using two previously developed ELISAs to separately quantify 12S and 146S particles. Virions completely dissociated into 12S particles within 3 months after oil-emulsification. Dissociation occurred at a much lower rate in a comparable aqueous solution that was not oil-emulsified. Thus, oil-emulsification stimulates virion dissociation, presumably due to the protein denaturing effect of the oil–water interface. In real-time stability studies the stability of oil-adjuvanted virions of four different FMDV strains was significantly increased by addition of sucrose and BSA in a synergistic manner. Contrary to BSA addition, the effect of sucrose addition was concentration dependent. This study illustrates the importance of analysing antigen integrity after oil-emulsification and provides methods for FMDV vaccine stabilization.

Role of non-covalent interactions in the production of visco-elastic material from zein

The role of non-covalent interactions in the formation of visco-elastic material from zein was investigated. Hydrophobic interactions were evaluated through the addition of various salts from the Hofmeister series. Urea, ethanol, and beta mercaptoethanol (β-ME) were used to evaluate the effects of protein denaturation and disulfide bonds on zein’s ability to form a visco-elastic material. The addition of NaI and NaSCN altered the properties of visco-elastic materials made from zein, making them softer and more extensible, as did urea and ethanol. The addition of NaCl and Na2SO4 negatively impacted the ability of zein to from a visco-elastic material and at higher concentrations completely disrupted the formation of visco-elastic material. These results indicate that manipulating non-covalent interactions in zein can alter and in some cases, completely disrupt the formation of a visco-elastic material. Specifically this may be due to disruption of hydrophobic interactions within individual zein proteins or interactions between proteins. The reducing agent β-ME had little effect on zein’s ability to form a visco-elastic material. Therefore, the visco-elastic properties of zein arise as a result of non-covalent interactions.

Role of plant β-glucosidases in the dual defense system of iridoid glycosides and their hydrolyzing enzymes in Plantago lanceolata and Plantago major

The typical defense compounds of Plantaginaceae are the iridoid glycosides, which retard growth and/or enhance mortality of non-adapted herbivores. In plants, glycosidic defense compounds and hydrolytic enzymes often form a dual defense system, in which the glycosides are activated by the enzymes to exert biological effects. Yet, little is known about the activating enzymes in iridoid glycoside-containing plants. To examine the role of plant-derived β-glucosidases in the dual defense system of two common plantain species, Plantago lanceolata and Plantago major, we determined the concentration of iridoid glycosides as well as the β-glucosidase activity in leaves of different age. To investigate the presence of other leaf metabolites potentially involved in plant defense, we used a metabolic fingerprinting approach with ultra-high performance liquid chromatography coupled with time-of-flight-mass spectrometry. According to the optimal defense hypothesis, more valuable parts such as young leaves should be better protected than less valuable parts. Therefore, we expected that both, the concentrations of defense compounds as well as the β-glucosidase activity, should be highest in younger leaves and decrease with increasing leaf age. Both species possessed β-glucosidase activity, which hydrolyzed aucubin, one of the two most abundant iridoid glycosides in both plant species, with high activity. In line with the optimal defense hypothesis, the β-glucosidase activity in both Plantago species as well as the concentration of defense-related metabolites such as iridoid glycosides correlated negatively to leaf age. When leaf extracts were incubated with bovine serum albumin and aucubin, SDS-PAGE revealed a protein-denaturing effect of the leaf extracts of both plantain species, suggesting that iridoid glycosides and plant β-glucosidase interact in a dual defense system.

Effect of trimethylamine-N-oxide on pressure-induced dissolution of hydrophobic solute

Molecular dynamics simulations are performed to study the effects of increasing trimethylamine-N-oxide (TMAO) concentration on the pressure-induced dissolution of hydrophobic solutes immersed in water. Such systems are of interest mainly because pressure increases the dissolution of hydrophobic protein interior causing protein denaturation and TMAO acts to offset the protein denaturing effect of high hydrostatic pressures. In view of this, in this study, methane molecules are considered as model hydrophobic molecules and simulations are performed for four independent TMAO solutions each at four different pressures ranging from 2 to 8 kbar. From potentials of mean force calculations, it is found that application of pressure reduces the free energy difference between contact minimum (CM) and solvent-separated (SSM) minimum of hydrophobic solute, suggesting dissolution at high pressures. TMAO, on the other hand, increases the relative stability of CM state of methane molecules relative to its SSM state. High packing efficiency of water molecules around the hydrophobic solute at high pressure is observed. Also observed are TMAO-induced enhancement of water structure and direct hydrogen-bonding interaction between TMAO and water and the correlated dehydration of hydrophobic solute. From hydrogen bond properties and dynamics calculations, it is observed that pressure increases average number of water-water hydrogen bonds while reduces their life-times. In contrast, TMAO reduces water-water hydrogen bonding but enhances their life-times. These results suggest that TMAO can reduce water penetration into the protein interior by enhancing water structure and also forming hydrogen bonds with water and hence counteracts protein unfolding.

Membrane Bridging and Hemifusion by Denaturated Munc18

Neuronal Munc18-1 and members of the Sec1/Munc18 (SM) protein family play a critical function(s) in intracellular membrane fusion together with SNARE proteins, but the mechanism of action of SM proteins remains highly enigmatic. During experiments designed to address this question employing a 7-nitrobenz-2-oxa-1,3-diazole (NBD) fluorescence de-quenching assay that is widely used to study lipid mixing between reconstituted proteoliposomes, we observed that Munc18-1 from squid (sMunc18-1) was able to increase the apparent NBD fluorescence emission intensity even in the absence of SNARE proteins. Fluorescence emission scans and dynamic light scattering experiments show that this phenomenon arises at least in part from increased light scattering due to sMunc18-1-induced liposome clustering. Nuclear magnetic resonance and circular dichroism data suggest that, although native sMunc18-1 does not bind significantly to lipids, sMunc18-1 denaturation at 37°C leads to insertion into membranes. The liposome clustering activity of sMunc18-1 can thus be attributed to its ability to bridge two membranes upon (perhaps partial) denaturation; correspondingly, this activity is hindered by addition of glycerol. Cryo-electron microscopy shows that liposome clusters induced by sMunc18-1 include extended interfaces where the bilayers of two liposomes come into very close proximity, and clear hemifusion diaphragms. Although the physiological relevance of our results is uncertain, they emphasize the necessity of complementing fluorescence de-quenching assays with alternative experiments in studies of membrane fusion, as well as the importance of considering the potential effects of protein denaturation. In addition, our data suggest a novel mechanism of membrane hemifusion induced by amphipathic macromolecules that does not involve formation of a stalk intermediate.

Effect of sodium dodecyl sulfate on protein separation by hollow fiber flow field-flow fractionation

Effects of protein denaturation and formation of protein-sodium dodecyl sulfate (SDS) complexes on protein separation and identification were investigated using hollow fiber flow field-flow fractionation (HF5) and nanoflow liquid chromatography-electrospray ionization-tandem mass spectrometry (nLC-ESI-MS-MS). Denaturation and formation of protein-SDS complexes prior to HF5 separation resulted an increase in the retention of few protein standards due to unfolding of the protein structures and complexation, yielding ~30% increase in hydrodynamic diameter. In addition, low molecular weight proteins which could be lost from the HF membrane due to the pore size limitation showed an increase of peak recovery about 2-6 folds for cytochrome C and carbonic anhydrase. In the case of proteins composed of a number of subunits, denaturation resulted in a decrease in retention due to dissociation of protein subunits. A serum proteome sample, denatured with dithiothreitol and SDS, was fractionated by HF5, and the eluting protein fractions after tryptic digestion were analyzed for protein identification using nLC-ESI-MS-MS. The resulting pools of identified proteins were found to depend on whether the serum sample was treated with or without denaturation prior to the HF5 run due to differences in the aqueous solubility of the proteins. The enhancement of protein solubility by SDS also increased the number of identified membrane proteins (54 vs. 31).

Differential Scanning Calorimetry (DSC) Studies on the Thermal Properties of Peanut Proteins

Studies related to the functional and thermal properties of peanut proteins are limited if compared with other vegetable protein sources. The aim of this work was to study the thermal denaturation of peanut protein isolates (PPI) by DSC. The thermal profile of PPI showed two endothermic peaks (assigned to denaturation of arachin and conarachin fractions). The thermal stability of arachin and conarachin increased when water content decreased, and a critical water level was found for both fractions. The effect of protein denaturants was studied. Low contents of urea stabilized protein fractions, but lower T(d) values were found with increasing concentrations. DeltaH values of arachin were affected by urea. SDS affected DeltaH values and thermal stability of conarachin; the arachin fraction showed higher resistance to SDS-induced denaturation. DTT addition did not affect conarachin stability, although enthalpy values decreased significantly. On the other hand, arachin was greatly affected by DTT. In summary, thermal denaturation parameters of PPI were sensitive to water content, indicating that polar groups of arachin and conarachin contribute to structure stabilization. Urea addition mainly affected the structure of the arachin fraction, which was attributed to its higher surface hydrophobicity. Results obtained from SDS and DTT suggest that hydrophobic interactions and disulfide bonds play an important role in structure maintenance of arachin and conarachin.

The Influence of Urea and Trimethylamine-N-oxide on Hydrophobic Interactions

Molecular dynamics simulations are used to obtain potentials of mean force for pairs of neopentane molecules immersed in aqueous solutions containing urea, trimethylamine-N-oxide (TMAO), or both solutes at once. It is shown that the hydrophobic attraction acting between neopentane pairs in pure water and in water-urea solution is completely destroyed by the addition of TMAO. This strongly suggests that TMAO does not counter the protein denaturing effect of urea by enhancing hydrophobic attraction amongst nonpolar groups.

Novel in situ polymerized coatings for hydrophobic interaction chromatography media

Hydrophobic interaction chromatography (HIC) and other capture media are typically produced by grafting different ligands to base matrices at defined surface densities. This often complicates media production. An alternative approach to media involving in situ radical initiated polymerization was used to graft polymer coatings directly at Sepharose® polymeric base matrices. This method appears suitable for producing many different chromatography media on a variety of base matrices. In the present study, it also favorably increased the solution pressure-flow properties of a Sepharose base matrix used to produce HIC media. A wide range of HIC media could be produced by simply varying the reaction ratio of butyl vinyl ether, and hydroxybutyl vinyl ether. The new HIC media was evaluated using five test proteins (bovine serum albumin, ribonuclease A, α-chymotrypsinogen A, myoglobin and α-lactalbumin). The media exhibited classic HIC behavior, predictably controlled hydrophobicity, plus good protein selectivity, capacity (70 mg protein/ml gel) and often total protein recovery. By modifying the degree of matrix hydrophobicity, we could also reduce effects of protein denaturation often seen with conventional HIC and observed as multiple peaks in the chromatograms. Separation of crude protein extracts from Eschericha coli, expressing a green fluorescent protein (GFPuv) and, a more hydrophobic, recombinantly-modified, tyrosine-tagged green fluorescent protein (YPYPY-GFPuv), was also performed. These proteins were very stable, exhibited significantly different retention times, and could be used to study the ability of the media to work with complex protein mixtures. Such GFP mutants appear ideal for characterizing the performance of chromatographic media.

Structure and Interaction in Aqueous Urea−Trimethylamine-N-oxide Solutions

The structural and energetic properties of solutions containing water, urea, and trimethylamine-N-oxide (TMAO) are examined using molecular dynamics simulations. Such systems are of interest mainly because TMAO acts to counter the protein denaturing effect of urea. Even at relatively high concentration, TMAO is found to fit well into the urea-water structure. The underlying solution structure is influenced by TMAO, but these perturbations tend to be modest. The TMAO-water and TMAO-urea interaction energies make an important contribution to the total energy in solutions where counter-denaturing effects are expected. TMAO-water and TMAO-urea hydrogen bonds have the largest hydrogen-bond energies in the system. Additionally, TMAO cannot hydrogen bond with itself, and hence it interacts strongly with water and urea. These observations suggest that the mechanism of TMAO counter denaturation is simply that water and urea prefer to solvate TMAO rather than the protein, hence inhibiting its unfolding.

魚類筋原繊維タンパク質由来の生分解性フィルム形成メカニズム

In our previous study, semi-transparent and flexible biodegradable films were successfully prepared from myofibrillar proteins of blue marlin meat. The objective of this study was to elucidate the mechanism of film formation. Effect of pH on the amount of surface hydrophobicity and surface SH group in the film-forming solution, solubility of film proteins in various protein denaturant solutions, SDS-PAGE, and addition effect of protein denaturants in the film-forming solutions were investigated. At first, the necessity of unfolding of protein molecules was revealed for the formation of self-standing films. Secondly, the important chemical bondings involved in the protein-protein interactions were confirmed to be hydrophobic interaction for acidic condition, hydrogen bondings for neutral condition, and hydrophobic interaction and disulfide bondings for alkaline condition.

Binding of odorants to individual proteins and their mixtures. Effects of protein denaturation and association. A plasticized globule state

The unfolding-association-refolding behaviour of proteins and their interactions with odorants are significant to the processing and flavoring of foods. Interactions of 2-octanone and vanillin (aliphatic and aromatic odorants) with individual proteins and their mixtures have been studied using: native, acid and thermally denatured bovine serum albumin (BSA), native and thermally denatured ovalbumin (OA) and bovine β-casein (BC). Equilibrium dialysis and differential scanning calorimetry methods were used to study flavor binding and flavor release in protein solutions. The binding of vanillin to native BSA exhibited two equivalent binding sites with binding constants in the order of 103 M−1 and these binding parameters were not markedly changed within the range of temperature from 25 to 63 °C. The binding site number was monotonously reduced to about zero as the pH was decreased from 6.4 to 2.5, consistent with the N⇔F transition of BSA. The complete loss of vanillin binding activity was also coupled with both acid and thermal denaturation of BSA. Neither the associated BC nor thermally denatured OA produced a detectable competition with BSA for the binding of vanillin or octanone. The associated BC did not bind vanillin. It has been proposed that the adsorption of hydrophobic low-molecular weight compounds acts to plasticize the globule state of the protein. Plasticized globular proteins seem to tend towards self-association and refolding with separation of hydrophobic ligands (e.g. odorants).