Surface Sulfhydryl Groups Research Articles

Prior thermal and high-pressure processing alters the impact of high intensity ultrasound on reconstituted skim milk

Reconstituted skim milk was subjected to heat treatment at 85 °C for 20 min or high pressure processing (HPP) at 400 or 600 MPa for 15 min with or without subsequent high intensity ultrasound (US) at 68 kHz, 500 W for 15 min at 30 °C. Untreated and treated samples were analyzed for particle size distribution, zeta potential, surface hydrophobicity, and concentration of total and surface sulfhydryl groups in addition to Native- and SDS-PAGE of serum phase upon ultracentrifugation and pH adjustment. Preceding heat- and HPP altered the impact of the subsequent US treatment, demonstrating process- and intensity-dependent exposure and burial of surface reactive sites on milk proteins respectively. US following HPP promoted sedimentation of HPP-dispersed serum casein fractions, while US following heat was directed mainly at the whey proteins originally bound to the micelles. The primary US effect on the untreated and treated milk proteins was at the molecular level.

PH and ultrasound driven structure-function relationships of soy protein hydrolysate

The structural, thermodynamic and functional properties of soy protein hydrolysate (SPH) modified by treatment at different pH values (3, 5, and 9 and pH 7 as control) followed by ultrasound treatment (240 W, 30 min) were investigated. The treatment of SPH at alkaline pH combined with ultrasound treatment resulted in a reduction in the particle size and turbidity, enhancement in the surface negative charge and disulfide bond (SS) content, and exposure of more surface sulfhydryl (SH) groups, resulting in increased surface hydrophobicity and fluorescence intensity compared to those of the samples treated at pH 3–7. In addition, the alkaline-treated samples were more structurally stable than those treated at other pH values, having higher denaturation temperatures and enthalpies; moreover, these samples had higher solubility and emulsifying and foaming capacities. In addition, ultrasound-assisted pH treatment altered the secondary and tertiary structures of SPH by altering the covalent and non-covalent interactions, although there was no effect on the molecular weight distribution of proteins. In conclusion, ultrasound-assisted pH treatment is an effective method to improve physicochemical properties of SPH for applications in the food industry.

Pumpkin seed coat pigments affected aqueous enzymatic extraction processing through interaction with its interfacial protein

In this study, the oil recovery from pumpkin seed with or without the presence of pigment was evaluated during the aqueous enzymatic extraction process (AEEP). Additionally, the interaction of pumpkin seed coat pigment—protochlorophyll (Pchl) with interfacial proteins (globulin-O/W, globulin-W, and albumin-W) during the aqueous extraction process was investigated. When Pchl was removed from pumpkin seeds, the yield of free oil was significantly increased by 50.71% after the first centrifugation. And the total oil recovery increased from 68.59% to 89.91% using enzymatic demulsification. The β-sheet percentage of globulin-O/W decreased by 5.6% with the presence of Pchl based on the circular dichroism spectra analysis. The particle size of globulin-W and albumin-W significantly increased in contrast to globulin-O/W. In addition, the increase of surface hydrophobicity and surface sulfhydryl group showed a conformational change of three protein extracts. Fluorescence spectra analyses showed that Pchl quenched the intrinsic fluorescence of globulin-W, albumin-W, and globulin-O/W in a static mode. Thermodynamic analyses indicated that the main force between Pchl and proteins was hydrophobic interactions. The hydrolysis efficiency of Papain was reduced during demulsification in AEEP with the presence of Pchl. Therefore, the removal of pumpkin seed coat pigments facilitated the aqueous extraction of seed oil by getting rid of the interaction of Pchl with its interfacial protein.

Synthesis of sulfhydryl functionalized silicon quantum dots with high quantum yield for imaging of hypochlorite in cells and zebrafish.

Sulfhydryl functionalized silicon quantum dots (S-SiQDs) with a fluorescence quantum yield of 38.5% were synthesized using 3-mercaptopropyltrimethoxysilane (MPTMS) and m-phenylenediamine by a simple one-pot method. It is worth noting that by oxidizing the surface sulfhydryl groups and statically quenching, the fluorescence of S-SiQDs at 492nm (excitation at 383nm) can be selectively quenched by hypochlorite (ClO-) in a linear range of 0.05 to 1.8μM with a low detection limit of 13nM. The reaction was completed in 10s with no interference from other ROS, metal ions, anions and reducing species. The silicon source containing sulfhydryl groups was used to synthesize silicon quantum dots for the first time, and the surface of the S-SiQDs was provided with sulfhydryl groups and reacted rapidly and sensitively with ClO-. The S-SiQDs have good photostability and biocompatibility, and can be further used for ClO- imaging in MCF-7 cells and zebrafish, showing great promise in biological imaging. The proposed assay demonstrates that 3-mercaptopropyltrimethoxysilane is a good choice to obtain afunctionalized fluorescent nanoprobe for redox species.

New insights into the enhanced transport of uncoated and polyvinylpyrrolidone-coated silver nanoparticles in saturated porous media by dissolved black carbons

Silver nanoparticles (AgNPs) are among the most applied nanomaterials and have great potential to be present in the environment. Dissolved black carbon (DBC) is ubiquitous in soil as a result of large-scale application of biomass-derived black carbon as soil amendments, while its impacts on the transport of AgNPs remain unclear. In this study, two DBCs with different functional groups were prepared at 300 and 500 °C (DBC300 and DBC500), and their impacts on the transport of uncoated AgNPs (Bare-AgNP) and polyvinylpyrrolidone-coated AgNPs (PVP–AgNP) in saturated quartz sand were investigated. The transport of PVP-AgNP was much higher than Bare-AgNP under the same conditions because of the increased steric hindrance provided by PVP surface coating. The transport of two kinds of AgNPs was both enhanced by the DBCs under all the experimental conditions. DBC500 displayed a stronger enhancement effect than DBC300 on PVP-AgNP transport, but DBC300 facilitated the migration of Bare-AgNP more significantly than DBC500. The higher aromaticity and stronger hydrophobicity of DBC500 drove it to be adsorbed on the surface of PVP-AgNP, thus providing stronger steric hindrance and promotion effect on PVP-AgNP transport. However, DBC300 contained surface sulfhydryl groups, which bound with the Bare-AgNP tightly, therefore it greatly promoted Bare-AgNP transport via enhanced steric hindrance. (X)DLVO calculations indicated DBCs generally increased the energy barrier between the AgNPs and sand grains. The results shed light on the vital roles of both the properties of AgNPs and DBCs on the fate and environmental behaviors of silver nanomaterials in complex environments.

Antigenicity of β-lactoglobulin reduced by combining with oleic acid during dynamic high-pressure microfluidization: Multi-spectroscopy and molecule dynamics simulation analysis

Some food components can modulate the antigenicity of β-lactoglobulin (β-LG). This study investigated the role of oleic acid (OA) in reducing the antigenicity of β-LG. The results indicate the antigenicity of β-LG gradually decreased from 15 (sample with no OA) to 9.86, 7.51, and 6.01 µg/mL when interacting with OA during dynamic high-pressure microfluidization treatment at 0.1, 80, and 160 MPa. Although binding sites (n) of β-LG combined with OA at 0.1, 80, and 160 MPa decreased from 0.79 to 0.5 and 0.66, β-LG had a higher binding affinity (Ka) to OA than that of untreated β-LG. The values of Ka for β-LG/OA at 0.1, 80, and 160 MPa were 5.51 × 106, 17.43 × 106, and 49.75 × 106M-1, respectively. The molecule dynamic simulation showed that the OA molecules located at both β-barrel (site 1) interacted with Lys60, Glu62, and Lys69 and outer surface site 2 consisting of Tyr20, Tyr42, Ser21, Glu157, and His161. Additionally, when binding with OA during the dynamic high-pressure microfluidization treatment, the conformation of β-LG changed, reflected by the decrease of fluorescence intensity and total sulfhydryl group content, the increase of surface sulfhydryl group content, and secondary structure changes of β-LG. These results deduce that some epitopes may be masked by OA or modified by the conformational changes, resulting in the decline of antigenicity of β-LG molecules.

Antigenicity and conformational changes of β-lactoglobulin by dynamic high pressure microfluidization combining with glycation treatment

The combined effect of previous dynamic high-pressure microfluidization treatment (40, 80, 120, and 160MPa) and subsequent glycation with galacto-oligosaccharides (GOS) on the antigenicity of β-lactoglobulin (β-LG) was investigated. The antigenicity of β-LG-GOS decreased at relatively low pressure (≤120MPa). Surface sulfhydryl group content of β-LG-GOS increased and surface hydrophobicity of β-LG-GOS decreased. Additionally, protein unfolding in β-LG-GOS samples was reflected by quenching of fluorescence intensity, the red-shift of fluorescence spectra, decreased UV absorption, and circular dichroism analysis, indicating tertiary and secondary structural changes of β-LG. The conformational changes may contribute to the alteration of antigenicity.

Extraction of methylmercury and ethylmercury from aqueous solution using surface sulfhydryl-functionalized magnetic mesoporous silica nanoparticles

Surface sulfhydryl-functionalized magnetic mesoporous silica nanoparticles were prepared, aiming to extract trace alkylmercury from aqueous solution. The prepared nanoparticles were characterized by TEM, ED, EDX, DLS, FTIR, and SERS. Compare with that the non-sulfhydryl-functionalized Fe3O4@SiO2 exhibited almost no affinity for CH3Hg+ and CH3CH2Hg+; the sulfhydryl-functionalized Fe3O4@SiO2 exhibited high adsorption affinity for them, resulting from chelating interaction by surface sulfhydryl group, and the adsorption was not significantly impacted by pH within the range of 3.5–9.0 or coexisting metal ions. The monolayer adsorption on surface of Fe3O4@SiO2–RSH could reach equilibrium in 2min. Moreover, the CH3Hg+ and CH3CH2Hg+ adsorbed on Fe3O4@SiO2–RSH could be quickly separated from the matrix in a magnetic field and desorbed easily by acetonitrile and l-cysteine aqueous solution or HCl solution, and the recoveries were more than 80%. Findings of the present work highlight the potential for using Fe3O4@SiO2–RSH magnetic nanoparticles as effective and reusable adsorbents for extraction of ultra trace alkylmercury from environmental water samples.

Oxidative dissolution of 4C- and NC-pyrrhotite: Intrinsic reactivity differences, pH dependence, and the effect of anisotropy

The crystallographic diversity of pyrrhotite (Fe1−xS), one of the most common iron sulfide minerals, offers insights into how mineral–fluid interactions are controlled by crystal structures. We have conducted oxidative dissolution experiments on monoclinic 4C-pyrrhotite and ‘hexagonal’ NC-pyrrhotite in aqueous H2O2/H2SO4 and FeCl3/HCl media at pH between 1.8 and 2.9 using polished surfaces of single crystals. Quantification and detailed characterization of the reaction interfaces has been accomplished by confocal 3D topometry and transmission electron microscopy (TEM) in conjunction with focused ion beam (FIB) preparation. Crystallographically coherent intergrowths of 4C- and NC-pyrrhotite in a single sample allowed unambiguous identification of strong intrinsic reactivity differences between the two closely related phases. On {110} faces in the H2O2 medium at 35°C and pH below 2.70, NC-pyrrhotite (N∼4.85) reacts about 50–80% faster than 4C-pyrrhotite. Above pH 2.70, the behavior inverts and 4C-pyrrhotite dissolves faster, while overall reaction rates drop drastically by up to two orders of magnitude. Because the two pyrrhotite phases show only marginally different Fe/S ratios but substantial differences in structural complexity with regards to vacancy ordering, we attribute the reactivity differences to structurally controlled processes at the mineral–water interface. The transition at pH 2.70 is close to the reported isoelectric point of pyrrhotite. We attribute the pH dependent changes in reaction rates and behaviors to protonation/deprotonation of surface sulfhydryl groups and related changes in speciation and bonding mode of reactive oxygen species at the mineral interface. At pH <2.70, we find elemental sulfur as a frequent reaction product in H2O2 and FeCl3 media, indicating incomplete sulfur oxidation. Above pH 2.70, elemental sulfur was not found in H2O2 experiments (no data for FeCl3). Our results show that the effects of crystal anisotropy are strong and directional preference of dissolution changes at the pH 2.70 transition point as well, leading to complex sub-μm-scale textural development at the reaction interfaces throughout the pH range studied. High resolution TEM imaging of cross sections through reacted mineral surfaces show crystalline pyrrhotite up to the reaction interface and the absence of significant non-equilibrium layers or S-enriched (poly)sulfides.

Changes in conformation and in sulfhydryl groups of actomyosin of tilapia ( Orechromis niloticus) on hydrostatic pressure treatment

Actomyosin extracted from tilapia muscle was subjected to hydrostatic pressure treatment (50–300 MPa, 10–60 min, 4 °C) to investigate the changes in sulfhydryl groups and on conformation. Transmission electron microscopy showed that the structure of actomyosin was aggregated and disrupted above 100 MPa, and more regular network aggregates were observed as pressure increased. Moreover, pressurisation at 50 MPa for 10 min did not change actomyosin structures. Using SDS–PAGE analysis, molecules larger than the myosin heavy chain were observed when actomyosin was treated at and above 200 MPa. Below 200 MPa actomyosin formed aggregates, mainly with hydrogen bonds. Surface sulfhydryl group content of actomyosin increased with increased pressure, up to 250 MPa. However, total sulfhydryl group content of actomyosin decreased with increased pressure and time. According to this study, 200 MPa would be the critical pressure that induced actomyosin to form regular network structures.

Influence of pH-Induced Unfolding and Refolding of Egg Albumen on Its Foaming Properties

ABSTRACT: The foaming properties of egg albumen, which had been subjected to low and high pH unfolding followed by refolding, were investigated. The foaming capacity of egg albumen, the stability of the foam, or both, could be improved by an unfolding and refolding regime by choosing proper unfolding and refolding pH values. The foaming capacities of egg albumen were greatly improved when the refolding was at pH 6.5, 7.5, or 8.5, whereas the foaming capacities could be either slightly increased or decreased when the refolding was at pH 4.5 or 5.5 compared with the controls. The foam stability was in almost all cases improved by the unfolding and refolding treatments except for a few cases of unfolding at pH 1.5 or 10.5. The foam stability and liquid drainage were improved most when the unfolding was at pH 12.5. Analysis of total and surface sulfhydryl groups, surface hydrophobicity, and protein analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) provided strong evidence that the partial unfolding of egg albumen proteins as well as the interactions among egg albumen proteins through disulfide and/or hydrophobic groups dictated the improvements in foaming properties. The increase in surface hydrophobicity showed better correlation with the improvement of foaming properties than the change of surface sulfhydryl content did.

Extracellular Disulfide Exchange and the Regulation of Cellular Function

An emerging concept is that disulfide bonds can act as a dynamic scaffold to present mature proteins in different conformational and functional states on the cell surface. Two examples are the conversion of the receptor, integrin alphaIIbbeta3, from a low affinity to a high affinity state, and the interaction of CD4 receptor with the HIV-1 envelope glycoprotein gp120 to promote virus-cell fusion. In both of these cases there is a remodeling of the protein disulfide bonding pattern. The formation and rearrangement of disulfide bonds is modulated by a family of enzymes known as the thiol isomerases, which include protein disulfide isomerase (PDI), ERp5, ERp57, and ERp72. While these enzymes were reported originally to be restricted in location to the endoplasmic reticulum, in some cells thiol isomerases are found on the cell surface. This may indicate a wider role for these enzymes in cell function. In platelets it has been shown that reagents that react with cell surface sulfhydryl groups are capable of blocking a number of functional responses, including integrin-mediated aggregation, adhesion, and granule secretion. Furthermore, the use of function blocking antibodies to either PDI or ERp5 causes inhibition of these functional responses. This review summarizes current knowledge of the extracellular regulation of disulfide exchange and the implications of this in the regulation of cell function.

高圧極限環境を利用した食品加工における新展開 高圧処理による食品タンパク質のアレルゲン性低減化

This paper describes general methods to eliminate or decrease the allergenicity of food protein, and also describes high pressure-induced elimination of the allergenicity of food protein, especially meat protein.The effect of high pressure treatment on the elimination of bovine serum albumin (BSA, the major beef allergen) allergenicity was evaluated on the basis of histamine release from human basophilic KU812F cells sensitized with sera from allergic patients, and the structural changes of BSA responsible for reducing allergenicity was estimated. BSA pressurized at pressures ranging from 300 to 600 MPa reduced histamine release from the cells sensitized with A5 serum with significance. The reducing effect of high-pressure treatment gradually increased with the increase of pressure applied to BSA. The pressure-induced structural changes of BSA were estimated by fluorescence spectra, circular dichroism (CD) spectra (the content of secondary structure), the amount of surface sulfhydryl (SH) group, and the surface aromatic hydrophobicity. The blue shift and decrease of the fluorescence of BSA gradually progressed with the increase of pressure applied. But no significant effect of pressure on CD spectra was observed. Pressure-treated BSA showed the maximum increase in the amount of SH group by pressure treatment at 100 MPa, and the aromatic hydrophobicity gradually decreased with the increase of high pressure applied. These results indicated that high pressure treatment induced the tertiary structural changes of BSA, but no effect on the secondary structure. We concluded that the pressure-induced elimination of BSA allergenicity seemed to be related to the tertiary structural change of BSA.

기능성 어육단백질의 젤화 특성과 산업적 응용-1. 가열변성 중 화학결합에 미치는 pH의 영향

The effect of pH on surface hydrophobicity, sulfhydryl group, infrared spectrum, SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) pattern and enthalpy was investigated in recovered protein from mackerel and frozen blackspotted croaker by alkaline processing. Hydrophobic residue in myofibrillar protein exposed to the surface of protein, and hydrophobic interaction were the highest around 6. The surface hydrophobicity was different between myofibrillar protein and myofibrillar protein including sarcoplasmic protein (recovered protein). The peak at 1636 c was increased with pH, and the recovered protein was unfolded in alkali pH. Difference of surface and total sulfhydryl group at pH 7.0 and 10 was comparative high, and decrease of surface sulfhydryl group indicated formation of S-S bonds. Mackerel and frozen blackspotted croaker in alkaline pH showed bands of polymerized myosin heavy chain on SDS-PAGE pattern. The transition temperatures of recovered protein were 33.1, 44.3 and 65.5. Gelation of recovered protein from alkali processing was estimated by increase of -sheet structure by pH treatment, S-S bonds by oxidation of surface sulfhydryl group in heating, polymerization of myosin heavy chain in order.r.

Physical and Molecular Properties of Egg‐white Lipid Films

ABSTRACT:Polyethylene glycol‐plasticized films were cast from alkaline (pH 11.25), heated (45 °C for 20 min), aqueous egg white (EW) solutions, with or without (10% or 20% w/w of EW) milkfat (two fractions), oleic acid, or egg yolk lysophospho‐lipid (LPL). The lipids did not reduce (P &gt; 0.05) film water vapor permeability. Oleic acid increased (P &lt; 0.05) tensile strength and elongation, and surface sulfhydryl group (SH) concentrations in EW solutions. Oleic acid probably increased negative charges on EW proteins, unfolding protein chains, and exposing SH groups. LPL also slightly increased (P &lt; 0.05) surface SH concentrations in non‐heated mixtures. Electrophoretic patterns suggested oleic acid interactions with ovalbumin, ovotransferrin, and lysozyme. No lysinoalanine was in film‐forming mixtures based on lysine measurements.

Functional improvements in dried egg white through the Maillard reaction.

The effects of the Maillard reaction on the functional properties of dried egg white (DEW) were investigated. Maillard-reacted DEW (M-DEW) was prepared by storing sugar-preserved DEW (SP-DEW) at 55 degrees C and 35% relative humidity for 0-12 days. The M-DEW developed an excellent gelling property, and hydrogen sulfide production from heat-induced M-DEW gels decreased. Surface sulfhydryl (SH) group content of M-DEW increased while total SH group and alpha-helix contents decreased with increasing heating time in the dry state. Breaking strength, breaking strain, water-holding capacity, and hydrogen sulfide of heat-induced M-DEW gels significantly correlated with surface and total SH group contents in M-DEW. SDS-PAGE revealed that M-DEW proteins were polymerized in which covalent bonds were involved. The present study demonstrated that the Maillard reaction partially unfolds and polymerizes proteins of SP-DEW and, consequently, improved gelling property of SP-DEW under certain controlled conditions.

Tensile, Solubility, and Electrophoretic Properties of Egg White Films as Affected by Surface Sulfhydryl Groups

ABSTRACTFilms plasticized with polyethylene glycol were cast from alkaline (pH 10.5, 11.0, or 11.5), aqueous egg white (EW) solutions with or without heating (40°C for 30 min). Prior to casting, concentration of surface sulfhydryl (SH) groups was determined and they increased (P &lt; 0.05) (3.81–19.45 μM/g protein) with both pH and heating, presumably due to protein denaturation and cleavage of disulfide (S‐S) bonds. Concentration of surface SH groups correlated (P &lt; 0.05) with film tensile strength (r = 0.70), elongation at break (r = 0.86), and film total soluble matter (r =−0.94). Most likely, surface SH groups formed S‐S bonds through air oxidation and/or sulfhydryl/disulfide interchange, thus contributing to EW film formation. SDS‐PAGE patterns in presence or absence of 2‐mercaptoethanol confirmed occurrence of S‐S bonding in dried EW films.

QSARs for the effect of benzaldehydes on foodborne bacteria and the role of sulfhydryl groups as targets of their antibacterial activity.

Quantitative structure activity relationships (QSARs) were obtained describing the activity of a series of benzaldehydes against three different foodborne bacteria, Listeria monocytogenes F6861, serotype 4b, Salmonella enteritidis, Phage type 4, P167807 and Lactobacillus plantarum INT.L11. MIC values at pH 6.2 and 35 degrees C were obtained for 11 phenolic benzaldehydes to produce multiple linear regression and artificial neural network models. For each organism, the models contained a steric parameter Vw and an electronic-steric parameter for ortho substituents Es degree. The benzaldehydes did not require to partition to produce their effect, shown by the lack of a lipophilic parameter in the models. This strongly suggests that they act on the outside of the cells. Substitution ortho to the carbonyl group increased their antibacterial action. Cells were treated with 2,3-dihydroxy benzaldehyde and examined for their ability to bind radiolabelled iodoacetate to envelope sulfhydryl groups that remained available. It was shown that the accumulation of radiolabelled iodoacetate was lower after treatment, indicating possible competition between these two compounds for the same target. The order of the sensitivity to benzaldehydes (Salmonella > Listeria > Lactobacillus) correlated with the number of surface sulfhydryl groups available, being highest for Salmonella.

Acid adaptation sensitizes Salmonella typhimurium to hypochlorous acid.

Acid adaptation of Salmonella typhimurium at a pH of 5.0 to 5.8 for one to two cell doublings resulted in marked sensitization of the pathogen to halogen-based sanitizers including chlorine (hypochlorous acid) and iodine. Acid-adapted S. typhimurium was more resistant to an anionic acid sanitizer than was its nonadapted counterpart. A nonselective plating medium of tryptose phosphate agar plus 1% pyruvate was used throughout the study to help recover chemically stressed cells. Mechanisms of HOCl-mediated inactivation of acid-adapted and nonadapted salmonellae were investigated. Hypochlorous acid oxidized a higher percentage of cell surface sulfhydryl groups in acid-adapted cells than in nonadapted cells, and sulfhydryl oxidation was correlated with cell inactivation. HOCl caused severe metabolic disruptions in acid-adapted and nonadapted S. typhimurium, such as respiratory loss and inability to restore the adenylate energy charge from a nutrient-starved state. Sensitization of S. typhimurium to hypochlorous acid by acid adaptation also involved increased permeability of the cell surface because nonadapted cells treated with EDTA became sensitized. The results of this study establish that acid-adapted S. typhimurium cells are highly sensitized to HOCl oxidation and that inactivation by HOCl involves changes in membrane permeability, inability to maintain or restore energy charge, and probably oxidation of essential cellular components. This study provides a basis for improved practical technologies to inactivate Salmonella and implies that acid pretreatment of food plant environments may increase the efficacy of halogen sanitizers.

P-Chloromercurobenzene sulfonate inhibition of active Cl- transport in plasma membrane vesicles from Aplysia gut

Both a Cl(+)-stimulated adenosinetriphosphatase (ATPase) activity and an ATP-dependent Cl- transport process were found in Aplysia foregut absorptive cell plasma membranes. In an attempt to further characterize this transport process, plasma membrane vesicles from Aplysia foregut absorptive cells were prepared utilizing differential centrifugation and sucrose density-gradient techniques. Sulfhydryl ligand participation in ATP-dependent Cl- transport was confirmed in three ways. First, 1,4-dithiothreitol partially restored a p-chloromercurobenzene sulfonate (PCMBS)-inhibited ATP-dependent Cl- transport. Second, 1,4-dithiothreitol restored intravesicular negativity inhibited by PCMBS. Third, 1,4-dithiothreitol had no effect on either ATP-dependent Cl- transport or ATP-dependent intravesicular negativity inhibited by N-ethylmaleimide. These results are consistent with the hypothesis that surface sulfhydryl groups participate in the functioning of the active electrogenic Cl- transport mechanism in Aplysia gut.