Monocarboxylic Amino Acids Research Articles

Allosteric and substrate site effects of relevant amino acids on structural stability and flexibility of glutamate dehydrogenase-1 (GDH-1).

Mammalian GDH-1, which converts glutamate to alpha-ketoglutarate and ammonia while reducing NAD(P), is constitutively expressed in virtually all cells of the body. The extensive literature on GDH-1 suggests that functionally relevant GDH-1 structures may be distributed over a conformational flexibility landscape: polyhexamer, hexamer, trimer, monomer, monomer (unfolded), monomer (misfolded), polymer (disassembled). We have used both intrinsic (tryptophan) and extrinsic (ANS) fluorescent probes to study the dependence of the reversible hexamer to trimer dissociation on the concentrations of the denaturing agents urea and guanidine hydrochloride (GdnHCl). Dissociation at each denaturant concentration increases with increase in concentration and/or temperature, and these dependencies are shown to be affected by amino acids which bind to allosteric and/or substrate binding sites. Dissociation of the hexamer is accompanied by a large increase in the fluorescence of ANS due to binding to increase in exposed hydrophobic microdomains on the protein. In contrast, tryptophan fluorescence decreases due to increased exposure of tryptopan in the protein to the aqueous environment. Measurement were made of the influence of several known substrates and allosteric modifiers (i.e. a selection physiologically relevant monocarboxylic amino acids) on the GDH-1 hexamer to trimer transition. The observed effect of adding each amino acid is consistent with independent measurements of its binding affinity. From the temperature dependence of the fluorescence intensity changes for ANS we obtained activation parameters for the hexamer-trimer transitions. Our data are consistent with the hexamer/trimer transition in GDH-1 having significant regulatory function in vivo, perhaps contribution to/complementing allosteric regulation of the enzyme activity.

Carboxylic acids as efficient corrosion inhibitors of aluminium alloys in alkaline media

The efficiency of AA5754 aluminium alloy corrosion inhibition achieved with maleic, malic, succinic, tartaric, citric, tricarballylic acids and serine in alkaline environment (pH 11) was examined. Selected corrosion inhibitors are characterized by different numbers and distribution of carbonyl and hydroxyl groups within their molecules. We have proposed and verified a novel approach for determining the adsorption isotherms based on the impedance measurements in galvanostatic mode (g-DEIS), allowing to distinguish subtle changes in the adsorption dynamics. It was shown that g-DEIS precisely determines the inhibitor concentration required for the full coverage of aluminium surface with the adsorbed inhibitor monolayer. Our approach was then cross-verified with the ellipsometry, cyclic polarization and classic EIS measurements, while the SEM and XPS analyses served to determine changes in the surface topography and chemistry. We have demonstrated that the investigated compounds significantly decelerate the corrosion rate of AA5754 at low inhibitor concentrations. Inhibition efficiency exceeds 99% at 6.9 mM for tricarballylic, 8.1 mM for citric and 12.0 mM for tartaric acid. The inhibition efficiency was primarily dependent on the high number of carbonyl groups in the molecule, while the inhibition provided by monocarboxylic amino acid (serine) was negligible, reaching 60% at 20 mM. The plotted isotherms fitted the Langmuir adsorption model, with similar values of Gibbs free energy for each studied inhibitor. The adsorption of carboxylic acids onto the surface of aluminium occurred via ligand exchange mechanism. On the basis of electrochemical and XPS studies, we claim that the role played by hydroxyl groups is secondary, while their presence slightly worsens the corrosion resistance of aluminium.

A novel mechanism of V‐type zinc inhibition of glutamate dehydrogenase results from disruption of subunit interactions necessary for efficient catalysis

Bovine glutamate dehydrogenase is potently inhibited by zinc and the major impact is on V(max) suggesting a V-type effect on catalysis or product release. Zinc inhibition decreases as glutamate concentrations decrease suggesting a role for subunit interactions. With the monocarboxylic amino acid norvaline, which gives no evidence of subunit interactions, zinc does not inhibit. Zinc significantly decreases the size of the pre-steady state burst in the reaction but does not affect NADPH binding in the enzyme-NADPH-glutamate complex that governs the steady state turnover, again suggesting that zinc disrupts subunit interactions required for catalytic competence. While differential scanning calorimetry suggests zinc binds and induces a slightly conformationally more rigid state of the protein, limited proteolysis indicates that regions in the vicinity of the antennae regions and the trimer-trimer interface become more flexible. The structures of glutamate dehydrogenase bound with zinc and europium show that zinc binds between the three dimers of subunits in the hexamer, a region shown to bind novel inhibitors that block catalytic turnover, which is consistent with the above findings. In contrast, europium binds to the base of the antenna region and appears to abrogate the inhibitory effect of zinc. Structures of various states of the enzyme have shown that both regions are heavily involved in the conformational changes associated with catalytic turnover. These results suggest that the V-type inhibition produced with glutamate as the substrate results from disruption of subunit interactions necessary for efficient catalysis rather than by a direct effect on the active site conformation.

Equilibrium Studies of Binary and Ternary Complexes Involving Tricine and Some Selected a-Amino Acids

The formation equilibria for the binary complexes of CoII, NiII, CuII, ZnII, CdII, MnII, PbII, ThIV, UO2 II, and CeIII with tricine and for the ternary complexes involving some α-amino acids (glycine, α-alanine, proline, serine, asparagine, and aspartic acid) were investigated using pH-metric technique. The formation of binary and ternary complexes was inferred from the pH-metric titration curves. It was deduced that tricine acts as a primary ligand in the ternary complexes involving the monocarboxylic amino acids (glycine, α-alanine, proline, serine, and asparagine), whereas it behaves as a secondary ligand in the ternary systems containing the dicarboxylic aspartic acid. The ternary complex formation was found to take place in a stepwise manner. The stability constants of the complexes formed in aqueous solutions were determined potentiometrically under the experimental conditions (t=25°C, I=0.1 mol dm−3 NaNO3). The order of stability of the ternary complexes in terms of the nature of the amino acids is investigated and discussed. The values of Δlog K for the ternary complexes have been evaluated and discussed. Evaluation of the effects of ionic strength and temperature of the medium on the stability of the ternary system M II-tricine-α-alanine (M II=CoII, NiII, and CuII) has been studied. The thermodynamic parameters were calculated and discussed.

Conversion of a glutamate dehydrogenase into methionine/norleucine dehydrogenase by site‐directed mutagenesis

In earlier attempts to shift the substrate specificity of glutamate dehydrogenase (GDH) in favour of monocarboxylic amino-acid substrates, the active-site residues K89 and S380 were replaced by leucine and valine, respectively, which occupy corresponding positions in leucine dehydrogenase. In the GDH framework, however, the mutation S380V caused a steric clash. To avoid this, S380 has been replaced with alanine instead. The single mutant S380A and the combined double mutant K89L/S380A were satisfactorily overexpressed in soluble form and folded correctly as hexameric enzymes. Both were purified successfully by Remazol Red dye chromatography as routinely used for wild-type GDH. The S380A mutant shows much lower activity than wild-type GDH with glutamate. Activities towards monocarboxylic substrates were only marginally altered, and the pH profile of substrate specificity was not markedly altered. In the double mutant K89L/S380A, activity towards glutamate was undetectable. Activity towards L-methionine, L-norleucine and L-norvaline, however, was measurable at pH 7.0, 8.0 and 9.0, as for wild-type GDH. Ala163 is one of the residues that lines the binding pocket for the side chain of the amino-acid substrate. To explore its importance, the three mutants A163G, K89L/A163G and K89L/S380A/A163G were constructed. All three were abundantly overexpressed and showed chromatographic behaviour identical with that of wild-type GDH. With A163G, glutamate activity was lower at pH 7.0 and 8.0, but by contrast higher at pH 9.0 than with wild-type GDH. Activities towards five aliphatic amino acids were remarkably higher than those for the wild-type enzyme at pH 8.0 and 9.0. In addition, the mutant A163G used L-aspartate and L-leucine as substrates, neither of which gave any detectable activity with wild-type GDH. Compared with wild-type GDH, the A163 mutant showed lower catalytic efficiencies and higher K(m ) values for glutamate/2-oxoglutarate at pH 7.0, but a similar k(cat)/K(m) value and lower K(m) at pH 8.0, and a nearly 22-fold lower S(0.5) (substrate concentration giving half-saturation under conditions where Michaelis-Menten kinetics does not apply) at pH 9.0. Coupling the A163G mutation with the K89L mutation markedly enhanced activity (100-1000-fold) over that of the single mutant K89L towards monocarboxylic amino acids, especially L-norleucine and L-methionine. The triple mutant K89L/S380A/A163G retained a level of activity towards monocarboxylic amino acids similar to that of the double mutant K89L/A163G, but could no longer use glutamate as substrate. In terms of natural amino-acid substrates, the triple mutant represents effective conversion of a glutamate dehydrogenase into a methionine dehydrogenase. Kinetic parameters for the reductive amination reaction are also reported. At pH 7 the triple mutant and K89L/A163G show 5 to 10-fold increased catalytic efficiency, compared with K89L, towards the novel substrates. In the oxidative deamination reaction, it is not possible to estimate k(cat) and K(m) separately, but for reductive amination the additional mutations have no significant effect on k(cat) at pH 7, and the increase in catalytic efficiency is entirely attributable to the measured decrease in K(m). At pH 8 the enhancement of catalytic efficiency with the novel substrates was much more striking (e.g. for norleucine approximately 2000-fold compared with wild-type or the K89L mutant), but it was not established whether this is also exclusively due to more favourable Michaelis constants.

The neurotoxin, β- N-methylamino- l-alanine (BMAA) interacts with the strychnine-insensitive glycine modulatory site of the N-methyl- d-aspartate receptor

Electrophysiological and receptor binding techniques were used to determine whether the neurotoxin β- N-4-methylamino- l-alanine (BMAA), a monocarboxylic amino acid, can act at the strychnine-insensitive glycine modulatory site to modify the activity of N-methyl- d-aspartate receptors. dl-BMAA but not l-BMAA reversibly potentiated the amplitude of NMDA-activated currents. Neither dl-BMAA nor l-BMAA were able independently to activate currents. The reversal potential and the potential-dependence of the amplitude were not affected by dl-BMAA. The dl-BMAA effect was reversibly antagonized by 7-chlorokynurenic acid. Concentration jump experiments showed that the time course of the “off” response of NMDA-activated currents in the presence of dl-BMAA is faster than in the presence of glycine, suggesting that dl-BMAA dissociates from the receptor more rapidly than glycine. dl-BMAA produced a concentration-dependent displacement of [ 3H]glycine binding which was additive with that of 7-chlorokynurenic acid. These data indicate that d-BMAA could act as a stereospecific modulator of NMDA receptor function by acting as an agonist at the strychnine-insensitive glycine modulatory site of the NMDA receptor.

A pH-dependent activation-inactivation equilibrium in glutamate dehydrogenase of Clostridium symbiosum

1. On transferring Clostridium symbiosum glutamate dehydrogenase from pH 7 to assay mixtures at pH 8.8, reaction time courses showed a marked deceleration that was not attributable to the approach to equilibrium of the catalysed reaction. The rate became approximately constant after declining to 4-5% of the initial value. Enzyme, stored at pH 8.8 and assayed in the same mixture, gave an accelerating time course with the same final linear rate. The enzyme appears to be reversibly converted from a high-activity form at low pH to a low-activity form at high pH. 2. Re-activation at 31 degrees C upon dilution from pH 8.8 to pH 7 was followed by periodic assay of the diluted enzyme solution. At low ionic strength (5 mM-Tris/HCl), no re-activation occurred, but various salts promoted re-activation to a limiting rate, with full re-activation in 40 min. 3. Re-activation was very temperature-dependent and extremely slow at 4 degrees C, suggesting a large activation energy. 4. 2-Oxoglutarate, glutarate or succinate (10 mM) accelerated re-activation; L-glutamate and L-aspartate were much less effective. 5. The monocarboxylic amino acids alanine and norvaline appear to stabilize the inactive enzyme: 60 mM-alanine does not promote re-activation, and, as substrates at pH 8.8 for enzyme stored at pH 7, alanine and norvaline give progress curves showing rapid complete inactivation. 6. Mono- and di-nucleotides (AMP, ADP, ATP, NAD+, NADH, NADP+, CoA, acetyl-CoA) at low concentrations (10(-4)-10(-3) M) enhance re-activation at pH 7 and also retard inactivation at pH 8.8. 7. The re-activation rate is independent of enzyme concentration: ultracentrifuge experiments show no changes in molecular mass with or without substrates. 8. The activation-inactivation appears to be due to a slow pH-dependent conformational change that is sensitively responsive to the reactants and their analogues.

Synthesis and vascular activity examination of 3-dimethoxyphosphoryl propyl esters of N-acyl derivatives of neuroactive monocarboxylic amino acids

Synthesis and vascular activity examination of 3-dimethoxyphosphoryl propyl esters of N-acyl derivatives of neuroactive monocarboxylic amino acids

Structural requirements for activation of the glycine receptor that modulates the N-methyl-D-aspartate operated ion channel

It has recently been demonstrated that glycine can potentiate several measures of N-methyl-D-aspartate (NMDA)-induced channel opening, including radioligand binding to the PCP receptor. These data suggest that the NMDA/PCP receptor complex may be allosterically modulated by a binding site for glycine. We report here that several other monocarboxylic amino acids enhance NMDA-induced [ 3H]TCP binding and displace [ 3H]glycine binding with similar apparent affinities and stereoisomerism. The results are discussed with relation to the structural requirements for compounds to bind to this site.

Titrations in non-aqueous media. Part X. Potentiometric and conductimetric titrations of amino acids with tetrabutylammonium hydroxide in pyridine and acetonitrile solvents.

Of the 22 α-amino acids studied, all but three (tyrosine, cystine and cysteine) have been titrated potentiometrically using a standard solution of tetrabutylammonium hydroxide in two solvent systems, 90% pyridine-water and 90% acetonitrile-water. The half-neutralisation potentials and the corresponding pK′a1 and pK′a2 values of the amino acids in these solvent systems have been calculated. Potentiometric titrations of binary mixtures of the two dicarboxylic amino acids, glutamic and aspartic acid, with the other monocarboxylic amino acids have also been carried out. The end-points of the titrations performed in the 90% acetonitrile-water solvent system were found to be much sharper than those of the titrations carried out in the 90% pyridine-water solvent system. All the determinations of amino acids, either in single or in binary mixtures, have been shown to have an error of less than ±2%.The α-amino acids and their binary mixtures with glutamic and aspartic acids have also been titrated conductimetrically in the same two solvent systems. Almost all the titrations gave either no end-points or non-stoicheiometric end-points. It has been shown that the solvent systems used in this work are suitable for potentiometric titrations of amino acids, but are not suitable for the conductimetric titrations.

Heparin-like activity of insoluble sulphonated polystyrene resins Part III: Binding of dicarboxylic amino acids

It has been demonstrated previously that polystyrene sulphonate possesses anticoagulant properties and that the binding of some amino acids could enhance the heparin-like properties of such resins. These properties depend on the surface density of the active groups, the nature and binding of the group and on the net charge borne by the polymer. In this paper, we describe the preparation of copolystyrene (sulphonate-dicarboxylic amino acid sulphamide) resins. By measuring their antithrombic-surface-activity, we demonstrate that the activity developed by each carboxyl group is at least roughly the same as the activity of one sulphonate group, except in the case of aspartic acid sulphamide resin for which a cooperative effect is shown. The anticoagulant properties of resins bearing phosphonate or mono-carboxylic amino acid sulphamides are also examined.

Kinetic studies of Ox-liver glutamate dehydrogenase oxidative deamination of two glutamate analogues, L- threo-γ-methylglutamate and L-α-amino-γ-nitraminobutyrate, in the presence of the allosteric effector ADP

1. 1. Ox-liver glutamate dehydrogenase is known to utilise a wide range of amino acid substrates. Kinetic studies are presented here for L- threo-γ-methylglutamate and L-α-amino-γ-nitraminobutyrate in the presence of the allosteric effector ADP. 2. 2. The results presented are considered in the light of similar studies presented elsewhere in which the cofactor was systematically replaced by a variety of analogues. 3. 3. These amino acid analogues share the same pH optimum as glutamate, unlike the monocarboxylic amino acids including alanine and norvaline, and give linear double-reciprocal plots under the conditions used here. 4. 4. Studies with the alternative coenzymes have suggested an ordered addition of glutamate before coenzyme in the presence of ADP. The present results obtained under identical conditions support this conclusion.

CHEMICAL MEDIATION OF APPETITIVE FEEDING IN A MARINE DECAPOD CRUSTACEAN: THE IMPORTANCE OF SUPPRESSION AND SYNERGISM.

The California spiny lobster, Panulirus interruptus, failed to exhibit appetitive feeding or locomotion in response to a low molecular weight fraction (< 1000 daltons) prepared from a sea water extract of muscle from abalone, a natural prey. This lack of response was caused by chemical suppressants, rather than by lack of stimulatory compounds. Excitatory responses were induced by single, low molecular weight compounds, but these responses were inhibited by suppressants which occur naturally in the muscle fraction. Amino and organic acids were found highly stimulatory to lobsters, but nucleotides and sugars were not. A mixture of monocarboxylic amino acids and dicarboxylic organic acids was much more effective in elliciting behavior than either of the constituents tested alone, at the same overall concentration. Mixtures which combined either ammonium or urea with amino or organic acids significantly reduced behavioral activity caused by these latter substances. Results indicate that tests of single chemicals cannot always reliably predict the stimulatory properties of solutions, combining even as few as two or more compounds. The stimulatory properties of complex odorants, including prey extracts, are best assessed by fractionating and then combining and testing the fractions in bioassays of factorial design.

Ox liver glutamate dehydrogenase. The use of chemical modification to study the relationship between catalytic sites for different amino acid substrates and the question of kinetic non-equivalence of the subunits.

The effect of pyridoxal 5'-phosphate on the activity of ox liver glutamate dehydrogenase towards different amino acid substrates was investigated. Both alanine and glutamate activities decreased steadily in the presence of pyridoxal 5'-phosphate. The alanine/glutamate activity ratio increased as a function of inactivation by pyridoxal 5'-phosphate, indicating that glutamate activity is lost more rapidly than alanine activity. A mixture of NADH, GTP and 2-oxoglutarate completely protected the alanine and glutamate activities against inactivation by pyridoxal 5'-phosphate. The activity of glutamate dehydrogenase towards glutamate and leucine decreased steadily in a constant ratio in the presence of pyridoxal 5'-phosphate. The effect of leucine on the alanine and glutamate activities as a function of inactivation by pyridoxal 5'-phosphate was studied. The results are interpreted to suggest that the subunits of glutamate dehydrogenase hexamer are kinetically non-equivalent with regard to activity towards the two monocarboxylic amino acids as well as glutamate, and that all three substrates share the same active centre. However, leucine is also able to bind at a separate regulatory site.

Spectrophotometric observation of a glutamate dehydrogenase- l-glutamate complex

Ultraviolet differential spectroscopic measurements show the existence of a glutamate dehydrogenase ( l-glutamate:NAD(P) + oxidoreductase (deaminating), EC 1.4.1.3)— l-glutamate complex. The spectral features resemble perturbation difference spectra of enzyme aromatic amino acid chromophores and allow the determination of the l-glutamate concentration dependence. The dissociation constant for this enzyme- l-glutamate complex was approximately 48 mM and was independent of enzyme concentration. The lack of interaction between the binding of l-glutamate and the activating monocarboxylic amino acids indicates that they bind at totally separate sites.

On the Involvement of Calcium in Amino Acid Transport and Growth of the Fungus Achlya

When the transport of Ca++ and other bivalent cations was arrested in the filamentous coenocytic fungus Achlya the transport of amino acids and assimilation of these precursors into proteins was promptly terminated. Uptake of thymidine but not of uracil was inhibited. However, both DNA and RNA syntheses continued under these conditions of cation starvation. The addition of Ca++ to Ca++-deficient cells enhanced amino acid transport by about 100%. Ca++ uptake was continuous throughout the growth phase of the organism and when this uptake was terminated, growth ceased immediately. Ca++ may be required for incorporation into cell wall and membrane material possibly to maintain their functional and structural integrity. The requirement for Ca++ in growth is specific and neither Mn++, Mg++, Co++, nor Fe++ could substitute. Ba++ acted as a competitive inhibitor of Ca++. Whether Ca++ alone is required for amino acid transport is not clear and has proved difficult to resolve. Over 50% of the Ca++ taken up by cells during growth could not be removed by metabolic poisons such as 2,4-dinitrophenol (DNP), azide, or cycloheximide, by chelators, or by simple exchange after growth was inhibited. The chelators (ethylenediaminetetraacetic acid and ethylene glycol bis(β-aminoethyl ether)-N ,N′-tetraacetic acid) and di- and tricarboxylic acids were not transported into the cells either in acid or alkaline buffers. The cells probably lack transporters necessary to effect this transfer. Dicarboxylic amino acids, aspartate and glutamate, on the other hand, were transported slowly in acid pH buffers whereas at neutral pH they were transported more effectively but still less efficiently than the monocarboxylic amino acids. Metabolic poisons, azide, DNP, and Hg++ inhibited the transport of amino acids, thymidine, uracil, and Ca++. Cycloheximide, on the other hand, did not inhibit the transport of amino acids, Ca++, uracil, and thymidine. We propose that the effect of calcium in Achlya metabolism is pleiotropic. Ca++ may be involved in (a) maintaining the structural and functional integrity of the cell membrane; (b) transport of amino acids although it is possible that other cations play a role as well; and (c) regulating protein biosynthesis by mediating transport of amino acids.

Inactivation of Phage by Aldehydes and Aldoses and Subsequent Reactivation

Summary and Conclusions Inactivation of phage by aldehydes and other substances depends on the concentration of the reacting substances, the time, the temperature and the pH of the substrate. At 37 C and pH = 7.5 a given volume of an undiluted broth phage was completely inactivated by an equal volume of a 0.05 percent solution of formaldehyde in 24 hours. Increasing concentrations of formaldehyde, or increasing dilutions of phage reduce the time of inactivation. The reaction starts immediately and its rate is an exponential function of time. Glyceraldehyde inactivated phage in the same molecular concentration as formaldehyde. Addition of formaldehyde or glyceraldehyde to phage in broth increases the acidity of the solution. Glucose, glucoseamine and fructose also inactivate phage if proper concentrations are used. The process of inactivation of fructose differs radically from that with glucose. Maltose, sorbitol and sucrose do not inactivate phage. On diluting inactivated phage before or shortly after inactivation is completed, in a substrate consisting of a solution of peptone or aminoacids, free active phage is liberated. The reaction, phage-formaldehyde, proceeds apparently in two stages, and is reversible only after the first stage. The amount of phage recovered depends on the types of aminoacids or polypeptide present in the diluent. When pure aminoacid solutions were used, the maximal reactivation was given by diaminoaminoacids, followed by the aliphatic monocarboxylic aminoacids. The least effective were the di-carboxylic aminoacids. The group attached to the NH2 apparently influences the reactivating capacity. When phage is inactivated by other aldehydes or by aldoses the reactivation is slower and less complete than when inactivated with formaldehyde. Reactivation after inactivation with glucose or glyceraldehyde is much less complete, while with glucoseamine and acetaldehyde it occurs only when the reaction of inactivation is interrupted before it is completed. Evidently there is a difference in the intensity of action of the various substances. The phenomenon of reactivation may be accounted for on the basis of dissociation. It is assumed that in the first phase, at least, the aldehyde combines with the NH2 group of the phage (or virus) and that on dilution this compound dissociates, liberating both aldehyde and phage. By introducing appropriate aminoacids into the diluting substrate, the equilibrium is disturbed, aldehyde is bound by the NH2 group of the aminoacid and more phage dissociated. This process continues until a new equilibrium is reached or until all the phage is liberated. The reaction thus seems to correspond with that between the aldehydes and polypeptids.

Retention by the Soil of the Nitrogen of Several Amino Acids1

Preheating soil in an effort to inactivate any enzymes or other thermolabile catalysts in the soil had only a slight effect upon the ability of the soil to remove amino acids from percolating solutions. Though some evidence was obtained in support of the existence of small but thermostable, small but thermolabile, and either a weak microbial activity or a catalyst inactivated by toluene as responsible for the removal of nitrogen from percolating solutions of amino acids, still the most important factor in removing amino acids from solutions was adsorption by the solid phase of the soil. Adsorption isotherms of a number of the more soluble amino acids with preheated Yolo fine sandy loam were obtained by the usual laboratory methods of analyzing a series of equilibrium extracts from the soil. The dicarboxylic mono-amino acids, aspartic and glutamic, were most weakly adsorbed, the monocarboxylic mono-amino acids, glycine, alanine, leucine, and norleucine, were somewhat more strongly adsorbed, and the monocarboxylic amino acids with one or more nitrogen-containing radicals in addition to the alpha-amino radical, such as lysine, histidine, and arginine, were most strongly adsorbed--even more strongly so than the NH4 ion of NH4Cl. Evidence was obtained which indicates that lengthening the hydrocarbon chain in the amino acids or transferring the NH2 radical farther out on the chain away from the carboxyl group increases adsorption; and that replacing a hydrogen on the terminal carbon atom of the chain with a phenyl group decreases adsorption, while an OH substitution increases the adsorption some and an SH substitution increases it somewhat more.