Arginyl residues and anion binding sites in proteins

Characterization of essential arginine residues implicated in the renal transport of phosphate and glucose

We have characterized the reaction of arginine-specific reagents with the phosphate and glucose carriers of the kidney brush-border membrane. The inhibition of phosphate and glucose transport by phenylglyoxal follows pseudo-first-order kinetics. The rate of inactivation of phosphate transport by 50 mM phenylglyoxal was about 3-fold higher than that for glucose transport (kapp was 0.052 s-1 for the uptake of phosphate and 0.019 s-1 for the uptake of glucose). The order of the reaction, n, with respect to phenylglyoxal was 1.25 and 1.31 for the inactivation of phosphate and glucose transport, respectively. The inactivation of phosphate flux by p-hydroxyphenylglyoxal also follows pseudo-first-order kinetics, but the inhibition rate (kapp = 0.0012 s-1) was slower than with phenylglyoxal. The inactivation increased with the alkalinity of the preincubation medium for both phosphate and glucose fluxes and was maximal at pH 9.0. The inactivation of phosphate flux by phenylglyoxal depends upon the presence of an alkaline intravesicular pH. Extravesicular pH does not affect the reaction. Phenylglyoxal does not interfere with the recycling of the protonated carrier since phosphate uptake is inhibited independently of the pH used for transport measurements. Moreover, phenylglyoxal completely abolished trans stimulation by phosphate. Trans sodium inhibited phosphate uptake and abolished the pH profile of phosphate uptake.

Involvement of arginine residues in the allosteric activation and inhibition of Synechocystis PCC 6803 ADPglucose pyrophosphorylase

ADPglucose pyrophosphorylase (EC 2.7.7.27) from the cyanobacterium Synechocystis PCC 6803 was desensitized to the effects of allosteric ligands by treatment with the arginine reagent, phenylglyoxal. Enzyme modification by phenylglyoxal resulted in inactivation when the enzyme was assayed under 3P-glycerate-activated conditions. There was little loss of the catalytic activity assayed in the absence of activator. Pi, 3P-glycerate, and pyridoxal-P were able to protect the enzyme from inactivation, whereas substrates gave minimal protection. The protective effect exhibited by Pi and 3P-glycerate was dependent on effector concentration. MgCl2 enhanced the protection afforded by 3P-glycerate. The enzyme partially modified by phenylglyoxal was more resistant to 3P-glycerate activation and Pi inhibition than the unmodified form. Vmax at saturating 3P-glycerate concentrations and the apparent affinity of the enzyme toward Pi were decreased upon phenylglyoxal modification. Incorporation of labeled phenylglyoxal into the enzyme was proportional to the loss of activity. Pi and 3P-glycerate nearly completely prevented incorporation of the reagent to the protein. Results suggest that one arginine residue per mol of enzyme subunit is involved in the binding of allosteric effector in the cyanobacterial ADPglucose pyrophosphorylase.

Ring oxidized retinals form unusual bacteriorhodopsin analogue pigments

Three ring oxidized retinal analogues have been isolated from the exhaustive oxidation of all-trans retinal. All-trans 4-oxoretinal and 2,3-dehydro-4-oxoretinal have similar absorption maxima to that of all-trans retinal and have been shown to be in the 6-s-cis conformation in solution. Pigments formed with bacterioopsin exhibit absorption maxima (520 nm) blue-shifted from that of bacteriorhodopsin (bR), indicating a disturbance of the external point charge by the electronegative carbonyl moiety at the 4 position. The third analogue contains a ring contracted to a cyclopentenyl-alpha,beta-dione. Unlike the majority of retinals, this analogue displays a 6-s-trans conformation in solution and has a red-shifted absorption maximum at 435 nm. The resulting bR analogue pigment (515 nm) is formed five times faster than the other oxoretinal pigments. All three oxoretinal pigments show an irreversible 20 nm blue shift upon exposure to white light. The 4-oxo and 2,3-dehydro-4-oxoretinal pigments, after irradiation, undergo a small reversible blue shift (4-8 nm) on dark adaptation. These two pigments pump protons, although with slowed photocycle kinetics, demonstrating that these structural changes (addition of the carbonyl at the C-4 and insertion of a double bond in the ring) do not block the function of the pigment. Extraction of the C-15 tritiated analogue retinals from illuminated and non-illuminated pigments of all three oxoretinals yield identical results. Therefore, any crosslinking of these oxoretinals to the protein is by linkages which are unstable to the extraction procedures.

The specificity and Kd at physiological ionic strength of an ATP-binding site on cytochrome c suit it to a regulatory role

Cytochrome c binds ATP with marked specificity at a site that contains the evolutionarily invariant residue Arg-91. The binding of ATP to this site was studied using equilibrium gel filtration, equilibrium dialysis and affinity chromatography. At physiological ionic strength the affinity is such that the major change in occupancy coincides with the normal cellular ATP concentration range, and the degree of saturation is proportional to the ratio of [ATP]/[ADP]. The specificity of binding at this site is more a function of the degree of phosphorylation of the nucleotide, than of the nature of the nucleoside moiety. Thus under physiological conditions the degree of occupancy of this site is proportional to the energy state of the cell, providing a means for the regulation of the respiratory chain which is sensitive to cytoplasmic ATP levels.

Chemical modification of a functional arginine residue in diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) phosphorylase I from Saccharomyces cerevisiae

Phenylglyoxal, a reagent with high specificity for arginine residues, inactivated Ap4A phosphorylase I from Saccharomyces cerevisiae in a pseudo-first-order manner. The second-order rate constant was 11.5 +/- 2.5 M-1 min-1. The loss of activity was a linear function of the incorporation of [7-14C]phenylglyoxal. The incorporation of 1.9 +/- 0.4 mol of phenylglyoxal/mol of enzyme accounted for complete loss of activity. The specificity of inactivation by phenylglyoxal was tested in the presence of ApnA (n = 2-6), ADP, ATP and Pi. The substrates, Ap4A, Ap5A and Pi protected the enzyme against inactivation, but Ap2A, Ap3A and Ap6A did not. Ap4A, Ap5A and Pi reduced the rate of inactivation by about 70%, 60% and 37% respectively. The Ap4A phosphorolysis products, ADP and ATP, also partially protected the enzyme against inactivation by phenylglyoxal. Thus Ap4A phosphorylase I probably contains an arginine residue in the binding site for Ap4A.

Preparation and properties of des-Tyr98 and des-Arg97-Tyr98 acylphosphatase (muscular isoenzyme)

Previous NMR reports indicated that Tyr98, the C-terminal residue of the muscular form of acylphosphatase, is likely to be part of the enzyme's active site. In addition, there is evidence that an arginine residue participates to the catalyzed reaction, possibly as phosphate binding site. Among all Arg residues present in the muscular forms of acylphosphatase, four, i.e. Arg23, Arg74, Arg77, and Arg97, appear to be conserved in all species checked thus far. We prepared the des-Tyr98 and des-Arg97-Tyr98 derivatives of the native acylphosphatase to investigate the properties of both modified enzymes. The enzyme lacking Tyr98 was found to be catalytically less effective than the native one, whereas the des-Arg97-Tyr98 acylphosphatase was completely inactive. This evidence suggests that Arg97 participates directly to the active site catalytic mechanism. Fluorescence and CD spectra revealed that the latter enzyme could have been undergone some conformational change that could account for the loss of activity; on the other hand, the one-dimensional NMR spectra of either native and des-Arg97-Tyr98 enzymes were strictly similar, thus demonstrating that the removal of the two C-terminal residues does not markedly affect the fold of the enzyme. The results reported are proof of a critical contribution of Arg97 to the acylphosphatase active site; however, we cannot exclude that the function of this residue is merely to stabilize the active site conformation and dynamics.

rbcR [correction of rcbR], a gene coding for a member of the LysR family of transcriptional regulators, is located upstream of the expressed set of ribulose 1,5-bisphosphate carboxylase/oxygenase genes in the photosynthetic bacterium Chromatium vinosum

An open reading frame, rbcR, was identified 226 bp upstream of rbcAB, i.e., the ribulose 1,5-bisphosphate carboxylase genes expressed in the phototrophic purple bacterium Chromatium vinosum. Several features reveal that rbcR encodes a member of the LysR family of transcriptional regulators, in which an anomalous content of lysine and arginine residues (Lys/Arg anomaly) was found. The expression of rbcR in Escherichia coli as a protein fused to the N-terminal region of beta-galactosidase led to reduced expression of rbcAB. Thus, rbcR is likely to encode a trans-acting transcriptional regulator of rbcAB expression in C. vinosum.

Design of a helix-bundle cross-link: NMR and UV-visible spectroscopic analyses and molecular modeling of ring-oxidized retinals

In order to generate potential chemical cross-links for studying the chromophore binding site of bacteriorhodopsin and related helix-bundle proteins, MnO2 was used to oxidize all-trans-retinal's ring moiety. The structures and solution conformations of three ring-oxidized retinal analogues have been determined by using UV-visible absorption and 1H and 13C NMR spectroscopies, primarily with regard to (i) the introduction of a functional group at the ring end of the chromophore, (ii) the retention of the all-trans geometry of the polyenal side chain, and (iii) the torsional angle of the ring-polyenal bond. Analyses of their UV-visible absorption spectral parameters (lambda max, epsilon max, and vibrational fine structure) and NMR spectral parameters (1H-1H coupling constants, 1H and 13C NMR chemical shifts, and 1H homonuclear Overhauser effects) indicated the 4-oxo and the 2,3-dehydro-4-oxo derivatives both possess the twisted 6-s-cis conformation adopted by most six-membered ring analogues of retinal in solution or crystal. However, the alpha-dioxocyclopentenyl analogue exists in solution predominantly (70-80%) as the planar 6-s-trans conformer, similar to violerythrine chromophore analogues. In order to identify the minor solution forms, molecular modeling and geometry optimizations using the semiempirical molecular orbital method AM1 defined two additional symmetry-related minima at +/- 30-40 degrees in its C6-C7 torsional energy profile. Because the chromophores of bacterio- and halorhodopsins and sensory rhodopsins are bound as the 6-s-trans conformer [Harbison, G.S., Smith, S.O., Pardoen, J.A., Courtin, J.M.L., Lugtenburg, J., Herzfeld, J., Mathies, R.A., & Griffin, R.G. (1985) Biochemistry 24, 6955-6962; Baselt, D.R., Fodor, S.P.A., van der Steen, R., Lugtenburg, J., Bogomolni, R.A., & Mathies, R.A. (1989) Biophys. J. 55, 193-196], we suggest that the cyclopentenyl analogue's alpha-diketo function may be favorably positioned within the binding pocket and sufficiently reactive toward nucleophilic attack to cross-link an arginine located in or near the ring end of the chromophore cavity: Arg134 according to the current model of bacteriorhodopsin's tertiary structure [Henderson, R., Baldwin, J.M., Ceska, T.A., Zemlin, F., Beckmann, E., & Downing, K.H. (1990) J. Mol. Biol. 213, 899-929] or Arg82 as postulated from an alternate model constructed primarily to accommodate the external point charge contribution to bacteriorhodopsin's opsin shift.

Evidence that chemical modification of a positively charged residue at position 189 causes the loss of catalytic activity of iron-containing and manganese-containing superoxide dismutases

The Escherichia coli, Bacillus stearothermophilus, and human manganese-containing superoxide dismutases (MnSODs) and the E. coli iron-containing superoxide dismutase (FeSOD) are extensively inactivated by treatment with phenylglyoxal, an arginine-specific reagent. Arg-189, the only conserved arginine in the primary sequences of these four enzymes, is also conserved in the three additional FeSODs and five of the six additional MnSODs sequenced to date. The only exception is Saccharomyces cerevisiae MnSOD, in which it is conservatively replaced by lysine. Treatment of S. cerevisiae MnSOD with phenylglyoxal under the same conditions used for the other SODs gives very little inactivation. However, treatment with low levels of 2,4,6-trinitrobenzenesulfonate (TNBS) or acetic anhydride, two lysine-selective reagents that cause a maximum of 60-80% inactivation of the other four SODs, gives complete inactivation of the yeast enzyme. Total inactivation of yeast MnSOD with TNBS correlates with the modification of approximately five lysines per subunit, whereas six to seven acetyl groups per subunit are incorporated on complete inactivation with [14C]-acetic anhydride. It appears that the positive charge contributed by residue 189, lysine in yeast MnSOD and arginine in all other SODs, is critical for the catalytic function of MnSODs and FeSODs.

The influence of pH on substrate form specificity of phosphoenolpyruvate carboxylase purified from Crassula argentea

Purified phosphoenolpyruvate carboxylase from both the crassulacean acid metabolism plant Crassula argentea and the C4 plant Zea mays was shown by kinetic studies at saturating fixed-varying concentrations of free mg2+ to selectively use the metal-complexed form of phosphoenolpyruvate when assayed at pH 8.0. A similar response to added magnesium at high free phosphoenolpyruvate concentrations was obtained for both enzymes, consistent with the use of the complex as the substrate. Kinetic studies at pH 7.0 indicated that at this pH the total concentration of phosphoenolpyruvate (including both free and metal-complexed forms) could be used by the enzyme from C.argentea while the C4 enzyme still utilized the complex. The loss of specificity induced by the decrease in the pH of the assay medium was accompanied by a decrease in the Km of this enzyme for phosphoenolpyruvate whatever the form considered and an increase in Vmax/Km. In contrast, a similar decrease of pH led to an increased Km of the C4 enzyme for phosphoenolpyruvate and a decrease of Vmax/Km. For the enzyme from C. argentea (previously shown to contain an essential arginine at the active site), protection of activity by the different forms of substrate against inactivation by the specific arginyl reagent 2,3-butanedione changes markedly with pH. At pH 8.1, the metal complex is the better protector while at pH 7.0 free phosphoenolpyruvate gives the best protection consistent with the observed kinetic changes in substrate form utilization. The relationship between the enzyme affinity for substrate, substrate specificity, and the requirement for magnesium for substrate turnover is discussed.

The inositol 1,4,5-trisphosphate receptor binding sites of platelet membranes. pH-dependency, inhibition by polymeric sulphates, and the possible presence of arginine at the binding site

The present study was initiated to characterize the inositol 1,4,5-trisphosphate (InsP3)-binding site in human platelets that is involved in Ca2+ release. InsP3 binding to platelet membranes was measured in two ways; (1) by displacement of labelled InsP3 with unlabelled InsP3, as in previous studies, and (2) directly, using only radioactive InsP3 as ligand, over the concentration range 0.25-100 nM. At physiological pH (7.1) the binding data were best fitted by a model for a single saturable binding site, with KD = 11.8 nM and Bmax. = 1.4 pmol/mg of protein. At alkaline pH values (8.3 and 9.4) binding was best fitted by a two-site model, the second site being of higher affinity (KD = 0.75-1.2 nM) but lower concentration (Bmax. = 0.195-0.6 pmol/mg of protein). All binding of InsP3 was blocked by polymeric sulphates (heparin, dextran sulphate, polyvinyl sulphate) regardless of pH. The specific arginine-modifying reagent p-hydroxyphenylglyoxal irreversibly blocked InsP3 binding, suggesting the presence of arginine at the recognition site for InsP3 binding. NN'-dicyclohexylcarbodi-imide (DCCD) and 1-ethyl-3-(3-dimethylaminopropyl)carbodi-imide (ECCD), which are carboxy-group-specific reagents, blocked Ca2+ release, but not InsP3 binding, indicating the existence of another site that regulates Ca2+ release apart from the active centre for InsP3.

Site selectivity in the binding of inorganic anions to serum transferrin

Equilibrium constants for the sequential binding of two anions at the specific metal-binding sites of apotransferrin have been measured by difference ultraviolet spectroscopy in 0.1 M N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (Hepes) at pH 7.4 and 25 degrees C. Log K1 values for phosphate, phosphite, sulfate, and arsenate fall in the narrow range of 3.5-4.0, while the log K1 for bicarbonate is 2.73. No binding is observed for nitrate, perchlorate, or borate. A dinegative charge appears to be the most important criterion for anion binding. Equilibrium constants have also been measured for binding of anions to both forms of mono(ferric)transferrin. There appears to be a very small site selectivity (0.2 to 0.4 log units) for phosphate, arsenate, and phosphite that favors binding to the N-terminal site, but there is no detectable selectivity for binding of sulfate or bicarbonate. Comparison of the binding affinities and anion selectivity with literature data on anion-binding to protonated macrocyles and cryptates strongly supports the existence of specific anion-binding sites on the protein. Binding constants were also measured in 0.01 M Hepes. The anionic sulfonate group of the buffer appears to have a small effect on anion binding.

Specific recognition of sulfate esters by bindin, a sperm adhesion protein from sea urchins

Bindin specifically binds to egg surface sulfated fucan polysaccharides and mediates the attachment of sperm to the egg during fertilization. Sulfate esters are critical for this interaction. We have examined the effect of different anionic groups on the relative binding affinities of a series of homologous anionic polymers for bindin to determine the extent to which other charged moieties can substitute for sulfate. We found that bindin displays a remarkable specificity for sulfate- or sulfonic acid-containing polymers. The relative affinities of poly(vinyl sulfate) and poly(styrenesulfonic acid) are four orders of magnitude higher than polymers containing phosphate esters or carboxyl groups. The bindin-mediated aggregation of sea urchin eggs was inhibited by the sulfated polymers but not the other anionic polymers. This high degree of selectivity for sulfated polymers is not observed for the binding of the polyanions to most other proteins and basic polypeptides. These results suggest that the binding is not due to the formation of simple salt bridges, and that all three non-ester oxygen atoms of the sulfate groups are involved in multiple bonding interactions with a complementary 'docking site' on the bindin polypeptide. The orientation of the polysaccharide sulfate oxygen atoms relative to the protein binding site may be an important determinant of the specificity of polysaccharide binding.

Arginyl groups involved in the binding of Anabaena ferredoxin--NADP+ reductase to NADP+ and to ferredoxin

Chemical modification of ferredoxin--NADP+ reductase from the cyanobacteria Anabaena has been performed using the alpha-dicarbonyl reagent phenylglyoxal. Inactivation of both the diaphorase and cytochrome-c reductase activities, characteristic of the enzyme, indicates the involvement of one or more arginyl residues in the catalytic process of the enzyme. The determination of the rate constants for the inactivation process under different conditions, including those in which substrates, NADP+ and ferredoxin, as well as other NADP+ analogs were present, indicates the involvement of two different groups in the inactivation process, one that reacts very rapidly with the reagent (kobs = 8.3 M-1 min-1) and is responsible for the binding of NADP+, and a second less reactive group (kobs = 0.9 M-1 min-1), that is involved in the binding of ferredoxin. Radioactive labeling of the enzyme with [14C]phenylglyoxal confirms that two groups are modified while amino acid analysis of the modified protein indicates that the modified groups are arginine residues. The identification of the amino acid residues involved in binding and catalysis of the substrates of ferredoxin--NADP+ reductase will help to elucidate the mechanism of the reaction catalyzed by this important enzyme.

Evidence for an arginine residue at the coenzyme-binding site of Escherichia coli isocitrate dehydrogenase

The arginine-specific reagent phenylglyoxal inactivated the active, dephosphorylated, form of Escherichia coli isocitrate dehydrogenase rapidly in a pseudo-first-order process. Both NADP+ and NADPH protected the enzyme against inactivation. Phenylglyoxal appeared to react with one arginine residue per subunit, and the extent of the reaction was proportional to the extent of the inactivation. In contrast, the phosphorylated form of isocitrate dehydrogenase did not react detectably with phenylglyoxal. The data indicate that the coenzyme-binding site of isocitrate dehydrogenase contains a reactive arginine residue that is protected by phosphorylation, and are consistent with the hypothesis that phosphorylation of the enzyme occurs close to or at its active site.

Osteocalcin-hydroxyapatite interaction in the extracellular organic matrix of bone

Osteocalcin, a major noncollagenous matrix protein of bone, dentin, and cementum, is found in tight association with the calcium phosphate mineral phase of these tissues. This article reviews the structural data for osteocalcin relevant to mineral adsorption. The equilibrium-binding properties for Ca2+ ions and hydroxyapatite are considered, along with the apparent physicochemical effects of osteocalcin on bone mineral dynamics. Several of osteocalcin's possible biological activities (involvement in mineralization, chemoattraction, and leukocyte elastase inhibition) are discussed in relation to the mineral-adsorption characteristics of this protein.

A kinetic study of the effects of phosphate and organic phosphates on the activity of phosphoenolpyruvate carboxylase from Crassula argentea

The effects of phosphate and several phosphate-containing compounds on the activity of purified phosphoenolpyruvate carboxylase (PEPC) from the crassulacean acid metabolism plant, Crassula argentea, were investigated. When assayed at subsaturating phosphoenolpyruvate (PEP) concentrations, low concentrations of most of the compounds tested were found to stimulate PEPC activity. This activation, variable in extent, was found in all cases to be competitive with glucose 6-phosphate (Glc-6-P) stimulation, suggesting that these effectors bind to the Glc-6-P site. At higher concentrations, depending upon the effector molecule studied, deactivation, inhibition, or no response was observed. More detailed studies were performed with Glc-6-P, AMP, phosphoglycolate, and phosphate. AMP had previously been shown to be a specific ligand for the Glc-6-P site. The main effect of Glc-6-P and AMP on the kinetic parameters was to decrease the apparent Km and increase Vmax/Km. AMP also caused a decrease in the Vmax of the reaction. In contrast, phosphoglycolate acted essentially as a competitive inhibitor increasing the apparent Km for PEP and decreasing Vmax/Km. Inorganic phosphate had a biphasic effect on the kinetic parameters, resulting in a transient decrease in Km followed by an increase of the apparent Km for PEP with increasing concentration of phosphate. The Vmax also was decreased with increasing phosphate concentrations. Further, the enzyme appeared to respond to the complex of phosphate with magnesium. In the presence of a saturating concentration of AMP, no activation but rather inhibition was observed with increasing phosphate concentration. This is consistent with the binding of phosphate to two separate sites--the Glc-6-P activation site and an inhibitory site, a phenomenon that may be occurring with other phosphate containing compounds. High concentrations of phosphate with magnesium were found to protect enzyme activity when PEPC, previously shown to contain an essential arginine at the active site, was incubated with the specific arginyl reagent 2,3-butanedione, consistent with the binding of phosphate at the active site. Data were successfully fitted to a rapid equilibrium model allowing for binding of the phosphate-magnesium complex to both the activation site and the active site which accounts for the activation/deactivation observed at low substrate concentrations. Effects on the Vmax of the reaction are also addressed. Factors controlling the differential affinity of various effectors to the active site or activation site appear to include charge distribution, size, and other steric factors.

Functional carboxyl groups in the red cell anion exchange protein. Modification with an impermeant carbodiimide

Anion exchange in human red blood cell membranes was inactivated using the impermeant carbodiimide 1-ethyl-3-(4-azonia-4,4-dimethylpentyl)-carbodiimide (EAC). The inactivation time course was biphasic: at 30 mM EAC, approximately 50% of the exchange capacity was inactivated within approximately 15 min; this was followed by a phase in which irreversible exchange inactivation was approximately 100-fold slower. The rate and extent of inactivation was enhanced in the presence of the nucleophile tyrosine ethyl ester (TEE), suggesting that the inactivation is the result of carboxyl group modification. Inactivation (to a maximum of 10% residual exchange activity) was also enhanced by the reversible inhibitor of anion exchange 4,4'-dinitrostilbene-2,2'-disulfonate (DNDS) at concentrations that were 10(3)-10(4) times higher than those necessary for inhibition of anion exchange. The extracellular binding site for stilbenedisulfonates is essentially intact after carbodiimide modification: the irreversible inhibitor of anion exchange 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) eliminated (most of) the residual exchange activity: DNDS inhibited the residual (DIDS-sensitive) Cl- at concentrations similar to those that inhibit Cl- exchange of unmodified membranes: and Cl- efflux is activated by extracellular Cl-, with half-maximal activation at approximately 3 mM Cl-, which is similar to the value for unmodified membranes. But the residual anion exchange function after maximum inactivation is insensitive to changes of extra- and intracellular pH between pH 5 and 7. The titratable group with a pKa of approximately 5.4, which must be deprotonated for normal function of the native anion exchanger, thus appears to be lost after EAC modification.

Role of basic amino acids in the interaction of bindin with sulfated fucans

Bindin, the acrosomal sperm adhesion protein of the sea urchin Strongylocentrotus purpuratus, binds specifically and with high affinity (Kd = 10(-8) M) to egg sulfated fucans in the high ionic strength milieu of seawater (0.55 M salt). Previous studies indicated that the negatively charged sulfate groups of the polysaccharide are critical for binding which suggested a binding mechanism involving basic residues of bindin. We found that the binding of fucan to bindin or polyarginine is stable at the ionic strength of seawater, whereas the binding of fucan to polylysine or polyhistidine is inhibited by 50% or more at this ionic strength. Group-specific modification of either arginine, lysine, or histidine residues of bindin results in a substantial inactivation of fucan binding activity. Preincubation of bindin with fucan can almost completely protect bindin from inactivation by arginine-specific reagents, butanedione and phenylglyoxal, but only moderately slowed the inactivation by the histidine reagent diethyl pyrocarbonate. In contrast, prior fucan binding could not prevent loss of activity by the reaction of citraconic anhydride with lysine residues. Other sulfated polysaccharides which do not interact strongly with bindin did not protect binding from phenylglyoxal-mediated inactivation when 800-3000-fold more polysaccharide than fucan was used during the preincubation before modification. We found that the larger and more hydrophobic arginine-modifying reagents, camphorquinone-10-sulfonic acid and cyclohexanedione, fail to inactivate fucan binding, suggesting that essential arginine residues may reside in an environment with restricted accessibility to these reagents. Parallel kinetic studies monitoring [14C]phenylglyoxal incorporation and fucan binding inactivation indicate that several of the four total arginine residues may be critical for fucan binding.(ABSTRACT TRUNCATED AT 250 WORDS)

The action of arginine-specific reagents on ionic and gating currents in frog myelinated nerve

(1) The effect of arginine-specific reagents on the sodium current (INa), potassium current (IK) and gating current (Igat) of myelinated nerve fibres was investigated. (2) Externally applied camphorquinone-10-sulfonic acid (Cqs-OH) had little effect, but 50 mM Cqs-OH applied to the cut ends of the fibre progressively reduced the amplitude of INa without significantly altering its time course. After 30 min INa was reduced to 52% (pH 9.0) or 66% (pH 6.75-7.6) of the control value. IK was decreased to a similar extent without changing its kinetics. Igat was less affected than the ionic currents. (3) Externally applied phenylglyoxal markedly reduced INa and Igat, but many fibres were lost during or shortly after the treatment. A few min treatment with 5 mM phenylglyoxal at pH 9 reduced INa to 20% and the on-response of Igat to 69.5%. The effect was to a large extent irreversible. (4) External nitrophenylglyoxal and hydroxyphenylglyoxal significantly reduced INa and were less damaging than phenylglyoxal. INa was decreased to 34.5% by 10 mM nitrophenylglyoxal and to 28.3% by 20 mM hydroxyphenylglyoxal. The effect of nitrophenylglyoxal was little reversible, but that of hydroxyphenylglyoxal to a large extent reversible. 20 mM hydroxyphenylglyoxal reduced the on-response of Igat to 62.5% of the control value, i.e. much less than INa. (5) 5 mM phenylglyoxal, 10 mM nitrophenylglyoxal and 20 mM hydroxyphenylglyoxal shifted the steady-state inactivation curve by 10-15 mV to more negative values of membrane potential but did not affect the descending branch of the INa(E) curve. (6) 20-30 mM glyoxal, 20 mM 1,2-cyclohexanedione and 10 mM 4-hydroxy-3-nitrophenylglyoxal had no effect on INa. (7) The results are compatible with the idea that arginine residues are principal components of the sodium channel macromolecule.

The oxidation-state-dependent ATP-binding site of cytochrome c. Implication of an essential arginine residue and the effect of occupancy on the oxidation-reduction potential

Arg-91 is not part of the active site of cytochrome c that mediates binding and electron transfer, yet it is absolutely conserved in eukaryotic cytochromes c, indicating a special function. The physicochemical properties of analogues are unaffected by the modification of this residue, so they can be used with confidence to study the role of Arg-91. We have established limiting conditions under which this residue alone is specifically modified by cyclohexane-1,2-dione, and have subsequently shown that ATP, and to a lesser extent ADP or Pi, protects it from the action of the reagent in an oxidation-state-dependent manner. These observations strongly support the idea that this site exerts a controlling influence on cytochrome c activity in the electron transport or other cellular redox systems, and we have commenced a study of how that influence might operate. We find that the redox potentials of both cytochrome c and analogue are little affected by changing ATP or Pi concentrations.

Novel Ca2+-activated neutral protease from an aquatic fungus, Allomyces arbuscula

A Ca2+-activated neutral protease was purified to homogeneity from an aquatic Phycomycete fungus, Allomyces arbuscula. It requires millimolar concentrations of Ca2+ for activation (1.8 to 2 mM for 50% activation). Sr2+ can replace Ca2+ but at higher concentrations (4 mM for 50% activation). The enzyme is a dimer of 40-kilodalton subunits and contains six cysteine residues, three of which are revealed only after the addition of micromolar concentrations of Ca2+; the other three are free. Enzyme activity is strongly inhibited by SH-group inhibitors and some trypsin inhibitors (leupeptin and alpha-N-tosyl-L-lysine chloromethyl ketone). The enzyme lacks general trypsinlike specificity, since substrates containing tryptic cleavage sites are not cleaved nor is enzyme activity inhibited by other trypsin inhibitors. The enzyme has many functional similarities to the extensively characterized mammalian and avian Ca2+-activated neutral proteases but differs in its substrate specificity, inhibition by alpha-N-tosyl-L-phenylalanine chloromethyl ketone, and subunit structure. It is, nevertheless, presumed that this enzyme has a similar high order of specificity and is involved in the regulation of a specific growth function.

The effect of phenylglyoxal on the translocation of pyruvate in rat-heart mitochondria

The effect of phenylglyoxal, an arginine-specific reagent, on the translocation of pyruvate and on the binding of alpha-cyanocinnamate by rat-heart mitochondria has been studied. It has been found that both the uptake and the oxidation of pyruvate by mitochondria are inhibited by phenylglyoxal. The inhibitory potency increases with the increasing of the pH of the medium. Phenylglyoxal does not affect the transmembrane delta pH. Phenylglyoxal also inhibits the binding of alpha-cyanocinnamate to mitochondria. Substrates of the carrier, such as pyruvate itself and monochloroacetate, partially prevent the inhibition of alpha-cyanocinnamate binding by phenylglyoxal, whilst acetate has no effect in this respect. Phenylglyoxal affects only the affinity of the alpha-cyanocinnamate binding site(s), without changing their total number. The results obtained indicate that arginine residues are involved in the mechanism of pyruvate translocation and of alpha-cyanocinnamate binding in rat-heart mitochondria.

Inhibition of staphylococcal alpha-toxin by covalent modification of an arginine residue

The effects of 1,2-cyclohexanedione and phenylglyoxal on staphylococcal alpha-toxin were studied. Modification of one arginine residue in alpha-toxin was sufficient to render the toxin nonhemolytic with no conformational change. Modified alpha-toxin did not protect cells from hemolysis by native alpha-toxin. An arginine residue is therefore at or near the binding site of alpha-toxin. Trypsin digestion of modified alpha-toxin generated a 20 kDa fragment which was isolated using a boric acid gel column. Upon regeneration, this 20 kDa fragment was not recognized by a population of antibodies which prevented alpha-toxin binding. The fragment was recognized by antibodies directed against post-binding events. However, the antibinding antibodies recognized the intact modified toxin. This leads us to conclude that antibinding determinants are not found directly in the binding site or are conformationally masked.

The presence of functional arginine residues in phosphoenolpyruvate carboxykinase from Saccharomyces cerevisiae

Saccharomyces cerevisiae phosphoenolpyruvate carboxykinase (ATP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.49) is completely inactivated by phenylglyoxal and 2,3-butanedione in borate buffer at pH 8.4, with pseudo-first-order kinetics and a second-order rate constant of 144 min-1 X M-1 and 21.6 min-1 X M-1, respectively. Phosphoenolpyruvate, ADP and Mn2+ (alone or in combination) protect the enzyme against inactivation, suggesting that the modification occurs at or near to the substrate-binding site. Almost complete restoration of activity was obtained when a sample of 2,3-butanedione-inactivated enzyme was freed of excess modifier and borate ions, suggesting that only arginyl groups are modified. The changes in the rate of inactivation in the presence of substrates and Mn2+ were used to determine the dissociation constants for enzyme-ligand complexes, and values of 23 +/- 3 microM, 168 +/- 44 microM and 244 +/- 54 microM were found for the dissociation constants for the enzyme-Mn2+, enzyme-ADP and enzyme-phosphoenolpyruvate complexes, respectively. Based on kinetic data, it is shown that 1 mol of reagent must combine per enzyme active unit in order to inactivate the enzyme. Complete inactivation of the carboxykinase can be correlated with the incorporation of 3-4 mol [7-14C]phenylglyoxal per mol of enzyme subunit. Assuming a stoichiometry of 1:1 between phenylglyoxal incorporation and arginine modification, our results suggest that the modification of only two of the three to four reactive arginine residues per phosphoenolpyruvate carboxykinase subunit is responsible for inactivation.

Chemical modification of arginine residues in the lactose repressor

The lactose repressor protein was chemically modified with 2,3-butanedione and phenylglyoxal. Arginine reaction was quantitated by either amino acid analysis or incorporation of 14C-labeled phenylglyoxal. Inducer binding activity was unaffected by the modification of arginine residues, while both operator and nonspecific DNA binding activities were diminished, although to differing degrees. The correlation of the decrease in DNA binding activities with the modification of approximately 1-2 equiv of arginine per monomer suggests increased reactivity of a functionally essential residue(s). For both reagents, operator DNA binding activity was protected by the presence of calf thymus DNA, and the extent of reaction with phenylglyoxal was simultaneously diminished. This protection presumably results from steric restriction of reagent access to an arginine(s) that is (are) essential for DNA binding interactions. These experiments suggest that there is (are) an essential reactive arginine(s) critical for repressor binding to DNA.

New evidence for the essential role of arginine residues in anion transport across the red blood cell membrane

2,3-Butanedione, in the dark and in the presence of borate, reacts rapidly to inactivate the sulfate equilibrium exchange across the human red cell membrane. Reactivation occurs spontaneously after the removal of borate, indicating the reaction of butanedione with essential arginine residues. The inactivation of the transport system depends on the concentration of the reagent, on the incubation time and exhibits pseudo-first-order kinetics. Chloride ions are able to protect the transport system against inactivation with the reagent. This would suggest the participation of the modified residue in the substrate binding site. When the transport system is inhibited to 50-60% by butanedione, the transporter can still bind covalently the anion transport inhibitor 2H2DIDS up to 85 +/- 12% of its total binding capacity. 3H2DIDS concentration was either 3.15, 10 or 20 microM. Modification of resealed ghosts with 50 mM butanedione under conditions where the transport system is to more than 75% inhibited, causes a reduction of only about 30% of the reversibly bound 3H2DIDS.

Malonate transport in human red blood cells

Kinetic parameters of [2-14C]malonate uptake by the human erythrocyte membrane have been determined as Km, 24 mM and turnover number, 5 X 10(4) s-1. The translocation of this organic dianion is concentration, pH and temperature dependent. Competitive inhibition of malonate uptake by eosin and inorganic anions, strongly implies that a common route exists for both inorganic anions and organic dianions, namely the anion-exchange Band 3 protein. 14C-Malonate which is nonmetabolized in the erythrocyte, could be a useful probe for monitoring anion-exchange in reconstituted Band 3 systems.

Influence of chloride concentration and pH on the 36Cl efflux from depolarized skeletal muscle of Rana temporaria

1. 36Cl- efflux rates were measured in depolarized fibre bundles (predominantly fast fibres) from m. semitendinosus of Rana temporaria in order to investigate the influence of chloride concentration (20-400 mM) and external pH (pHo, 5.5-11.6) on chloride self-exchange. Usually, the bundles were depolarized to a membrane potential of virtually zero ([Cl-]i = [Cl-]o = [Cl-]) in 140 mM-K+ and 20 mM-Cl- combined with either 60 mM-SO4(2-) (+52 mM-sucrose) or 120 mM-methyl sulphate, gluconate or glucuronate. Various values of [Cl-] were obtained by adding KCl to the medium, keeping constant the concentration of relatively impermeant solutes and thus the fibre volume. 2. The chloride permeability, PCl, at pH 7.5 decreased with increasing [Cl-] above 50 mM. At [Cl-] less than 50 mM, PCl was about 4 X 10(-6) cm s-1. 3. PCl at pHo 7.5 and 5.6 was a hyperbolic function of [Cl-1] (greater than or equal to 50 mM), consistent with saturation kinetics of chloride self-exchange. 4. Methyl sulphate inhibited chloride self-exchange and may enter depolarized fibre membranes slowly. Comparison of PCl estimates in SO4(2-), gluconate, and glucuronate suggested that SO4(2-) and gluconate may interfere with chloride self-exchange at low [Cl-], and that glucuronate interferes the least. 5. A change from chloride equilibrium to an inward KCl gradient increased the 36Cl- efflux rate in acid media (pH less than 6.5) and decreased the efflux rate at pHo greater than or equal to 7. The effects were not due to changes of membrane potential and demonstrate a change of transport mode consistent with single-filing at high pH and dominant exchange diffusion at low pH. This result makes interpretation of the saturation kinetics difficult. 6. At constant [Cl-], PCl showed a bell-shaped dependence on pHo with a maximum around pH 8.5. The decrease of chloride permeability as the pH is decreased below 8.5 showed an apparent pK of about 7. PCl fell at very alkaline pH with an apparent pK of about 10. 7. The results are in agreement with previous observations of an external pH-sensitive control of PCl (pK approximately 7) and suggest that, in conditions close to chloride equilibrium, this control includes a transition between a dominant conductive channel conformation at high pH and a dominant non-conductive conformation at low pH.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemical modification of arginine residues in p-hydroxybenzoate hydroxylase from Pseudomonas fluorescens: a kinetic and fluorescence study

The flavoprotein p-hydroxybenzoate hydroxylase from Pseudomonas fluorescens was modified by several arginine-specific reagents. Modifications by 2,3-butanedione led to the loss of activity of the enzyme, but the binding of p-hydroxybenzoate and NADPH to the enzyme was little or not at all affected. However the formation of the enzyme-substrate complex of the modified enzyme was accompanied by an increase of the fluorescence of protein-bound FAD, in contrast to that of native enzyme which leads to quenching of the fluorescence. Enzyme modified by phenylglyoxal did not bind p-hydroxybenzoate nor NADPH. Quantification and protection experiments showed that two arginine residues are essential and a model is described which accounts for the results. Modification by 4-hydroxy-3-nitrophenylglyoxal reduced the affinity of the enzyme for the substrate and NADPH. The ligands offered no protection against inactivation. From this it is concluded that one arginine residue is essential at some stage of the catalysis. This residue is not associated with the substrate- or NADPH-binding site of the enzyme. Time-resolved fluorescence studies showed that the average fluorescence lifetime and the mobility of protein-bound FAD are affected by modification of the enzyme.