Deprotonation Of Amino Group Research Articles

Do Tyrosine Phenolic Groups Contribute to the Alkaline Transition in the Redox Potential of Cytochrome F?

Cytochrome f, a c-type cytochrome involved in the photosynthetic electron transport chain, has a significantly higher redox potential than most other c-type cytochromes, ranging +370 to +380 mV. Like cytochrome c, cytochrome f also exhibits an alkaline transition in which the redox potential becomes pH dependent at high pH. In the case of cytochrome c, this has been attributed to replacement of the methionine sulfur serving as the sixth iron ligand by a deprotonated amino group. This cannot be the cause for the alkaline transition in cytochrome f as there is no methionine ligand to the iron, the sixth position being occupied by the N-terminal amino group.

Structure of [Pb(Gly-H)]+ and the Monosolvated Water and Methanol Solvated Species by Infrared Multiple-Photon Dissociation Spectroscopy, Energy-Resolved Collision-Induced Dissociation, and Electronic Structure Calculations

Infrared multiple-photon dissociation (IRMPD) spectroscopy, collision-induced dissociation mass spectrometry, and theoretical calculations are combined to provide new insights into the structure and dissociation of lead(II) complexed with the conjugate acid of the amino acid glycine ([Pb(Gly-H)](+)) in the presence and absence of solvent. Unexpectedly, these experiments show the main site of lead(II) coordination to be the deprotonated amino group of glycine, with additional coordination to the carbonyl group. In such a structure lead(II) can act as an effective conduit for proton/hydrogen shifts, making H(2)O loss competitive with that of CO in the [Pb(Gly-H)](+) complex and leading to solvent deprotonation and formation of [PbOR(Gly)](+) (R = H, CH(3)) ions when solvent is present in the complex. The structural assignments based on IRMPD spectroscopy are complemented with isotopic labeling experiments (H(2)(18)O) and experiments done on the ethyl ester of glycine.

Structural features and oxidative stress towards plasmidDNA of apramycin copper complex

The interaction of apramycin with copper at different pH values was investigated by potentiometric titrations and EPR, UV-vis and CD spectroscopic techniques. The Cu(II)-apramycin complex prevailing at pH 6.5 was further characterized by NMR spectroscopy. Metal-proton distances derived from paramagnetic relaxation enhancements were used as restraints in a conformational search procedure in order to define the structure of the complex. Longitudinal relaxation rates were measured with the IR-COSY pulse sequence, thus solving the problems due to signal overlap. At pH 6.5 apramycin binds copper(II) with a 2 : 1 stoichiometry, through the vicinal hydroxyl and deprotonated amino groups of ring III. Plasmid DNA electrophoresis showed that the Cu(II)-apramycin complex is more active than free Cu(II) in generating strand breakages. Interestingly, this complex in the presence of ascorbic acid damages DNA with a higher yield than in the presence of H(2)O(2).

Mercury(II) complex formation with glutathione in alkaline aqueous solution

The structure and speciation of the complexes formed between mercury(II) ions and glutathione (GSH = L-glutamyl-L-cysteinyl-glycine) have been studied for a series of alkaline aqueous solutions (C(Hg2+) approximately 18 mmol dm(-3) and C(GSH) = 40-200 mmol dm(-3) at pH approximately 10.5) by means of extended X-ray absorption fine structure (EXAFS) and 199Hg NMR spectroscopy at ambient temperature. The dominant complexes are [Hg(GS)2](4-) and [Hg(GS)3](7-), with mean Hg-S bond distances of 2.32(1) and 2.42(2) angstroms observed in digonal and trigonal Hg-S coordination, respectively. The proportions of the Hg(2+)-glutathione complexes were evaluated by fitting linear combinations of model EXAFS oscillations representing each species to the experimental EXAFS spectra. The [Hg(GS)4](10-) complex, with four sulfur atoms coordinated at a mean Hg-S bond distance of 2.52(2) angstroms, is present in minor amounts (< 30%) in solutions containing a large excess of glutathione (C(GSH) > or = 160 mmol dm(-3)). Comparable alkaline mercury(II) cysteine (H2Cys) solutions were also investigated and a reduced tendency to form higher complexes was observed, because the deprotonated amino group of Cys(2-) allows the stable [Hg(S,N-Cys)2](2-) chelate to form. The effect of temperature on the distribution of the Hg(2+)-glutathione complexes was studied by comparing the EXAFS spectra at ambient temperature and at 25 K of a series of glycerol/water (33/67, v/v) frozen glasses with C(Hg2+) approximately 7 mmol dm(-3) and C(GSH) = 16-81 mmol dm(-3). Complexes with high Hg-S coordination numbers, [Hg(GS)3](7-) and [Hg(GS)4](10-), became strongly favored when just a moderate excess of glutathione (C(GSH) > or = 28 mmol dm(-3)) was used in the glassy samples, as expected for a stepwise exothermic bond formation. Addition of glycerol had no effect on the Hg(II)-glutathione speciation, as shown by the similarity of the EXAFS spectra obtained at room temperature for two parallel series of Hg(II)-glutathione solutions with C(Hg2+) approximately 7 mmol dm(-3), with and without 33% glycerol. Also, the 199Hg NMR chemical shifts of a series of 18 mmol dm(-3) mercury(II) glutathione solutions with 33% glycerol were not significantly different from those of the corresponding series in aqueous solution.

Synthesis, characterization and antiproliferative activity of metal complexes with the Schiff base derived from the condensation 1:2 of 2,6-diformyl-4-methylphenol and 5,6-diamino-1,3-dimethyluracil

A series of mononuclear complexes with Co(II), Ni(II), Cu(II), Zn(II), Hg(II), Mo(VI) and Pd(II) containing the ligand derived from the 1:2 condensation of 2,6-diformyl-4-methylphenol and 5,6-diamino-1,3-dimethyluracil (hereafter denoted as BDFDAAU) were synthesized. The complexes were characterized by elemental analysis, thermogravimetry (TG) and differential scanning calorimetry (DSC), IR, 1H, 13C and 15N NMR, UV–visible–near IR (UV–VIS–NIR), EPR and magnetic measurements. The deprotonated ligand in the phenolic oxygen shows a symmetric tridentate coordination mode through the two azomethine nitrogen atoms and the phenolic oxygen atom whereas the coordination of the neutral ligand takes place through the phenolic oxygen atom and one azomethine nitrogen atom. In the Mo(VI) complex, the ligand is bideprotonated in the phenolic oxygen and an amino group from one uracil unit; so, the coordination mode changes again into an asymmetric way: phenolic oxygen atom, one azomethine nitrogen atom and the nitrogen atom from the deprotonated amino group. The antiproliferative behaviour against the five human tumor cell lines (human neuroblastoma NB69, human breast cancer MCF-7 and EVSA-T, human glioma H4 and human bladder carcinoma cell line ECV) suggested a modulator behaviour, according to the concentration, of cell growth due to their estrogen-like characteristics.

The Reactivity of Hexa(N‐methylideneimine)CoIII Complexes towards Nucleophiles: Structure and Mechanism

AbstractThe reactivity of the hexa(N‐methylideneimine)CoIII complex [Co‐hmi‐(taci)2]3+ (taci = 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol) towards the nucleophiles ammonia, aniline and cyanide was investigated and the main products were identified by spectroscopic methods and by a crystal structure analysis. The relative energies of the complexes formed and those of possible stereo isomers were analysed by means of molecular mechanics calculations. In the reaction with NH3, two condensation products, [Co(La)]3+ and [Co(Lb)]3+, were identified with the two taci moieties linked by one or two N=CH–N(H)‐CH2–NH bridges, respectively. The reaction with aniline yielded the complex [Co(Lc)(Ld)]3+ (where Lc is a mono‐N‐methylated and Ld a phenylformamidine‐substituted taci), whereas the reaction with cyanide resulted in the formation of [Co(Le)]3+ having an NH–CH2–C(NH2)=N bridge between the two taci subunits. A mechanism that accounts for the different types of products can be suggested as follows: In [Co(La)]3+, [Co(Lb)]3+ and [Co(Lc)(Ld)]3+, N‐methylation was observed and this can be interpreted in terms of an intramolecular Cannizzaro type hydride shift. For [Co(La)]3+ and [Co(Lb)]3+ two subsequent addition steps of the nucleophile to adjacent imino groups must take place prior to the hydride shift, whereas for [Co(Lc)(Ld)]3+ the hydride shift appears to have already occurred after the first addition step of aniline to an imino group. Formation of [Co(Le)]3+ can be explained in terms of a nucleophilic attack of CN– to an imino group and a subsequent attack of a deprotonated amino group (which must have previously been formed by hydrolysis of a methylideneimino group) to the nitrile C‐atom. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)

Adsorption of Enantiomeric and Racemic Cysteine on a Silver Electrode − SERS Sensitivity to Chirality of Adsorbed Molecules

The adsorption of both (L- and D-) enantiomeric forms of cysteine on the silver electrode surface was studied by surface-enhanced Raman scattering spectroscopy (SERS) as a function of electrode potential and pH value of the solution. It was demonstrated that at potentials more positive than -0.7 V (for pH 3) or -0.8 V (for pH 2 or lower), in acidic environment L-cysteine molecules are adsorbed mainly as P(H) (gauche) conformer, in zwitterionic form with the COO- groups close to the surface. At more negative potentials, NH3+ groups deprotonate at the surface with simultaneous weakening of the interaction of the carboxylic groups with the surface. Spectroscopic evidence for at least partial protonation of the COO- groups at strongly acidic solutions was given by observing the C=O stretching band at frequency lowered by about 30 cm(-1) in comparison with that observed for crystalline cysteine hydrochloride. It points to the considerable enhancement of the strength of hydrogen bonds and may be ascribed to the formation of cyclic L-cysteine dimers at the electrode surface. In neutral and alkaline solutions, adsorbed L-cysteine molecules have deprotonated amino groups at wide potential range. Similar spectroelectrochemical experiments were performed for D-cysteine and for a racemic mixture of D,L-cysteine. As expected, results for D-cysteine were similar to those for L-cysteine. However, for racemic mixture at acidic pH, the spectral effects corresponding to potential-induced transition from adsorbed zwitterions to neutral molecule were considerably smaller. This effect was discussed in terms of stereoselective dimerization of cysteine molecule at the electrode surface.

Inter- and intra-molecular condensation patterns of (en)PdII with trans-[a2PtL2]2+ (a = am(m)ine, L = 2-aminopyridine): PtPd3 and Pt2Pd4 species with multiple amide bridges. Unexpected trapping of a pair of nitrate ions by a Pt2Pd4 double coneElectronic supplementary information (ESI) available: 1H NMR spectra of 2a, 4a and 5; views of the crystal structure of 5. See http://www.rsc.org/suppdata/dt/b3/b301708g/

Reaction of trans-[a2Pt(Hampy)2]X2 (a = NH3, 2; a = MeNH2, 3; Hampy = 2-aminopyridine; X = NO3 or ClO4) with an excess of [(en)Pd(H2O)2]2+ in aqueous solution leads to two types of condensation products: (i) tetranuclear PtPd3 species, in which the deprotonated “a” ligands (μ-NH2, μ-MeNH) and the deprotonated amino group of the 2-aminopyridine (ampy) ligands are chelated by two (en)PdII entities and in addition a single PdII ion (without en) cross-links the amido functions of ampy in a nearly linear fashion. The four metal ions thus form a diamond arrangement with a short (<2.5 A) Pt→Pd dative bond. (ii) Hexanuclear Pt2Pd4 species, in which (en)PdII moieties bridge exclusively amido groups of four ampy ligands in such a way that an open rectangular box (or double cone) is formed. This allows two nitrate counter ions to become inserted in the cavity of the +8 charged cation. Thus in both cases the ampy ligand acts as a μ3-ligand, either in an intramolecular or an intermolecular fashion.

ChemInform Abstract: Fluorescent Chemosensors Containing Polyamine Receptors

Chemosensors have attracted interest in many different scientific fields, such as environmental chemistry, medicine, and the processing and storage of information. These molecular-scale devices have the advantage of working on the same spatial scale as the chemical structures that are responsible for macroscopic behaviour observed in the environment or those associated with health problems. Moreover, they allow the construction of molecular-scale devices for information storage. In this review, we describe a family of chemosensors based on a polyamine receptor and a fluorescent signalling unit. Polyamine receptors are water-soluble ambidentate receptors; they are able to coordinate either metal ions, when sufficient deprotonated amino groups are available, or anionic species, when there are sufficient protonated amino groups. On the other hand, the use of fluorescent signalling units confers the advantage of an immediate visual response/signal.

Fluorescent Chemosensors Containing Polyamine Receptors

Chemosensors have attracted interest in many different scientific fields, such as environmental chemistry, medicine, and the processing and storage of information. These molecular-scale devices have the advantage of working on the same spatial scale as the chemical structures that are responsible for macroscopic behaviour observed in the environment or those associated with health problems. Moreover, they allow the construction of molecular-scale devices for information storage. In this review, we describe a family of chemosensors based on a polyamine receptor and a fluorescent signalling unit. Polyamine receptors are water-soluble ambidentate receptors; they are able to coordinate either metal ions, when sufficient deprotonated amino groups are available, or anionic species, when there are sufficient protonated amino groups. On the other hand, the use of fluorescent signalling units confers the advantage of an immediate visual response/signal.

Interaction between chitosan and uranyl ions: Part 1. Role of physicochemical parameters

This work is devoted to the comprehension of the sorption mechanism of uranyl ions on chitosan particle dispersions. The uranyl concentration measurements were obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) and we considered the role of various physicochemical parameters (pH; nature and concentration of added salts; degree of acetylation, DA). The use of appropriate calculation software allowed us to determine the chemical nature of uranyl species in solution in relation to these different parameters. The optimal pH of fixation has been found to be within 6.5–7.5 and can be related to the necessity of having both deprotonated amino groups and no carbonate ions, which are a strong complexant of uranyl ions, thus inhibiting their interaction with chitosan. The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allowed us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature.

Sequence-selective interaction between mercury(II) ions and the DNA dodecamer [d(GCCGATATCGGC)]2 studied by 1H NMR spectroscopy.

The palindromic dodecamer [d(GCCGATATCGGC)]2 has been titrated by Hg(ClO4)2 in order to study sequence dependent HgII ion interactions. The titration pattern as monitored by 1D and 2D 1H NMR is consistent with a transition to a new conformer of the dodecamer induced by HgII ions. At intermediate stages of the titration, the proton signals from the new conformer coexist with those of the original one, indicating slow exchange between the two forms on the NMR timescale. The data clearly show that there is no major alteration in the secondary structure, e.g. B-->Z-form or duplex-->hairpin transition. The intra- and inter-residue sequential walk is completed except for a break between T6 and A7. At a concentration level r = [HgII]/[nucleobase] < 0.20 all four central imino signals are present. This definitely excludes thymine N3 as a possible mercuration site. In the imino region of the spectra HgII ions induce a large upfield shift of the thymine imino resonance T8-N3H, while the other thymine resonance T6-N3H is unperturbed. The guanine imino signal G4-N1H shows a large downfield ring current shift caused by major conformational changes in the duplex. The complete titration experiment indicates that mercury, initially, binds selectively to the A5'-T8 base pair. A tentative model is proposed where mercury is cross-linking the two strands via thymine T8-O4 and the deprotonated amino group of the complementary adenine base A5'.

Characterization of reaction products of 2-thienylamine and 2-furfurylamine with bis(acetylacetonato)palladium(II)

2-Thienylamine (Hata) and 2-furfurylamine (Hafa) reacted with bis(acetylacetonato)palladium(II) [Pd(acac) 2] in dichloromethane at room temperature to give Pd(acac) 2(Hata) and Pd(acac) 2(Hafa), respectively. In refluxing toluene the former amine gave [Pd(acac)(ata)] 2, while with the latter no further reaction took place. In Pd(acac) 2(Hata) and Pd(acac) 2(Hafa) the amines were coordinated through the amino group, with one acac ligand as an OO chelate and the other γ-carbon bonded. X-ray analysis revealed that [Pd(acac)(ata)] 2 was a dimer where the palladium atoms were bridged by deprotonated amino groups and coordinated with OO chelating acac ligands.

Rat Cathepsin H-Catalyzed Transacylation: Comparisons of the Mechanism and the Specificity with Papain-Superfamily Proteases1

We found that rat cathepsin H showed strong transacylation activity under physiological conditions. It is a feature of cathepsin H to utilize amino acid amides not only as acyl-acceptors but also as acyl-donors in the reaction. The pH-dependence of the transacylation activity was distinct from those of other papain-superfamily proteases. The alkaline limb (pKapp = 7.5) could be regarded as the pKa of the alpha-amino group of the acyl-donor, which was also involved in the original amino-peptidase activity. The acidic limb (pKapp = 5.8) was suggested to be involved in the deacylation step, where amino acid amide attacked the acyl-intermediate as a nucleophile in place of water in the hydrolysis. Although the N alpha-deprotonated acyl-acceptor, which is supposed to govern the nucleophilic attack, has a small population in the acidic pH range (above pH5), the transacylation was detectable even at the acidic pH-range because of the high S1'-site binding ability and suitable nucleophilicity of the acyl-acceptor. In the transacylation between various amino acid amides, the S1 and S1' site appeared to prefer hydrophobic residues without and regardless of a branch at beta-carbon, respectively. From these results and the sequence homology in the papain superfamily, we concluded that the reaction was governed by the acyl-donor having a protonated amino group, the acyl-acceptor having a deprotonated amino group and the remarkable hydrophobic character (especially favoring tryptophan amide) of the S1' site, presumably reflecting the good conservation of Trp177 in papain-superfamily proteases.

Thermal behavior and crystal structure of dichloro [6-amino-1,3-dimethyl-5-(2-chlorophenylazo)uracilato] gold(III)

The title compound was obtained by reacting HAuCl 4 with the uracil derivative in ethanol. X-ray work ( P2 1/ c, a=11.896(6), b=12.331(5), c= 13.501(4) Å, β=121.46(3)°, R=0.038, 2096 observed reflections) shows that the crystal contains individual complex molecules in which the metal has a slightly distorted square-planar coordination. Two cis corners are occupied by Cl ligands. The uracil derivative forms a six-membered chelate ring via the deprotonated amino group and the phenyl- substituted nitrogen atom of the azo group. The thermal behavior of the free ligand and its Au complex has been determined from thermogravimetric and differential scanning calorimetric measurements.

PH-Dependent Inhibitory Effects of Tris and Lithium Ion on Intestinal Brush-Border Sucrase

Tris and two of its hydroxylated amine analogs were examined in a metal-free, universal n-butylamine buffer, for their interaction with intestinal brush border sucrase. Our recent three-proton-families model (Vasseur, van Melle, Frangne and Alvarado (1988) Biochem. J., 251, 667-675) has provided the sucrase pK values necessary to interpret the present work. At pH 5.2, 2-amino-2-methyl-l-propanol (PM) causes activation whereas Tris has a concentration-dependent biphasic effect, first causing activation, then fully competitive inhibition. The amine species causing activation is the protonated, cationic form. The difference between the two amines is related to the fact that Tris has a much lower pKa value than PM (respectively, 8.2 and 9.8). Even at pH 5.2, Tris (but not PM) exists as a significant proportion of the free base which, by inhibiting the enzyme fully competitively, overshadows the activating effect of the cationic, protonated amine. Above pH 6.8, both Tris and PM act as fully competitive inhibitors. These inhibitions increase monotonically between pH 6.5 and 8.0 but, above pH 8, inhibition by 2.5 mM Tris tends to diminish whereas inhibition by 40 mM PM increases abruptly to be essentially complete at pH 9.3 and above. As pH increases from 7.6 to 9.0, the apparent affinity of the free amine bases decreases whereas that of the cationic, protonated amines, increases. In this way, the protonated amines replace their corresponding free bases as the most potent inhibitors at high pH. The pH-dependent inhibition by 300 mM Li+ is essentially complete at pH 8, independent of the presence or absence of either 2.5 mM Tris or 40 mM PM. Even at pH 7.6, an excess (300 mM) of Li+ causes significant increases in the apparent Ki value of each Tris, PD (2-amino-2-methyl-1-3-propanediol) and PM, suggesting the possibility of a relation between the effects of Li+ and those of the hydroxylated amines which in fact are mutually exclusive inhibitors. The inhibitory results are interpreted in terms of a mechanistic model in which the free bases bind at two distinct sites in the enzyme's active center. Binding at the glucosyl sub-site occurs through the amine's free hydroxyl groups. This positioning facilitates the interaction between the lone electron pair of the deprotonated amino group with a proton donor in the enzyme's active center, characterized by a pK0 around 8.1. When this same group deprotonates, then the protonated amines acting as proton donors replace the free bases as the species giving fully competitive inhibition of sucrase.

Palladium(II) complexes of N,N-co-ordinating arylazouracil ligands: infrared spectroscopy, thermal properties, and X-ray crystal structure of trans-bis(6-amino-1,3-dimethyl-5-phenylazouracilato)palladium(II)

Palladium(II) forms the complexes [PdL2](1)–(4) on reaction of tetrachloropalladate(II) with 6-amino-5-arylazouracil derivatives (uracil = pyrimidine-2,4-dione) in ethanolic media, with the exception of 6-amino-5-(2′-chlorophenylazo)-3-methyluracil (HL5) which leads to the complex [Pd(HL5)2Cl2](5). The crystal structure of the complex bis(6-amino-1,3-dimethyl-5-phenylazouracilato)palladium(II), [PdL12](1), was determined by X-ray crystallography. The complex crystallizes in the monoclinic system, space group P21/c, with a= 7.404(2), b= 9.537(1), c= 17.420(4)A, β= 99.38(2)°, Z= 2, and R= 0.043. The structure consists of discrete [PdL12] molecules (L1= 6-amino-1,3-dimethyl-5-phenylazouracilate), in which L1 acts as a bidentate ligand through the nitrogen atom of the deprotonated amino group and the nitrogen atom of the azo group bonded to the phenyl ring, to give a square-planar PdN4 geometry with palladium(II) at the inversion centre. The entire molecule is planar with the exception of the phenyl rings which are twisted by 84.4(2)° about the C–N bond away from the co-ordination plane in order to overcome interligand steric crowding. On the basis of i.r. and thermal data a trans-square-planar structure is proposed for (5), the ligand being co-ordinated through the nitrogen atom of the 6-amino group. In the temperature range 230–320 °C this complex eliminates two molecules of HCl to give [PdL52](6). The solid-state parameters and mechanism for this reaction were determined.

Studies on internal nitroso group transfer. Nitrosation of thiomorpholine

The kinetics of nitrosation of thiomorpholine have been studied under different experimental conditions. At low nitrite concentration and high acidity the reaction rate is first order with respect to nitrite and thiomorpholine and independent of acidity. The results are interpreted through a mechanism in which the S-nitroso intermediate with a deprotonated amino group must acquire a boat conformation to facilitate the migration of the NO group from the sulphur to the nitrogen atom. The mechanism is supported by the low isotope effect observed when the reaction is studied in D2O. In the pH range 2.3–3.6 and high nitrite concentration, the reaction rate is second order with respect to nitrite, the accepted mechanism being the nitrosation of deprotonated thiomorpholine by dinitrogen trioxide.

Adsorption of α-amino acids on spherical TiO 2 particles

Adsorption of L-glutamic acid, L- ( + )-lysine, and DL-serine on amorphous Ti hydrous oxide has been investigated as a function of pH. Whilst the serine does not adsorb in the pH range between 3.5 and 8, the uptake of the other two amino acids shows a complex dependence on the pH and also occurs under conditions of strong electrostatic repulsion at pH>8. Hydrogen bonding between deprotonated amino groups and surface hydroxyl groups is suggested as a possible explanation for observed adsorption when electrostatic repulsion prevails.

Sensitivity of rat renal luminal and contraluminal sulfate transport systems to DIDS.

4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) was tested as an inhibitor of the sulfate transport systems in rat renal brush border and basolateral membrane vesicles. Na+-driven sulfate uptake into brush border membrane vesicles was half-maximally inhibited at 350 microM DIDS. Proton gradient-driven sulfate uptake into basolateral membrane vesicles was competitively inhibited by DIDS with a Ki of 2.4 microM. The Km for delta pH-driven sulfate uptake was 5.4 microM. The different affinities of the sulfate transport systems for DIDS correlated with different substrate specificities. The luminal transport system accepted a smaller range of anions than the contraluminal system and did not operate as a Na+-independent anion exchanger. After treatment of basolateral membrane vesicles with 50 microM DIDS at pH 8.4 for 30 min, an irreversible inhibition of sulfate uptake was observed. With brush border membranes, only a small irreversible inhibition was obtained. Lack of inhibition after treatment of basolateral membranes with DIDS at pH 6.4 indicated that DIDS reacted with deprotonated amino groups of the transport protein. Sulfate was protected from the irreversible inhibition by DIDS. Sodium-driven uptake of L-glutamate and methylsuccinate into basolateral membrane vesicles was not irreversibly inhibited by DIDS, indicating a specific action of DIDS on the contraluminal sulfate transport system. Irreversible and substrate-protectable inhibition of sulfate transport render DIDS suitable for future affinity labeling studies on the sulfate transport system in basolateral membranes.