Spacer arms in affinity chromatography: use of hydrophilic arms to control or eliminate nonbiospecific adsorption effects

Investigating Antiprotozoal Chemotherapies with Novel Proteomic Tools-Chances and Limitations: A Critical Review

Identification of drug targets and biochemical investigations on mechanisms of action are major issues in modern drug development. The present article is a critical review of the classical "one drug"-"one target" paradigm. In fact, novel methods for target deconvolution and for investigation of resistant strains based on protein mass spectrometry have shown that multiple gene products and adaptation mechanisms are involved in the responses of pathogens to xenobiotics rather than one single gene or gene product. Resistance to drugs may be linked to differential expression of other proteins than those interacting with the drug in protein binding studies and result in complex cell physiological adaptation. Consequently, the unraveling of mechanisms of action needs approaches beyond proteomics. This review is focused on protozoan pathogens. The conclusions can, however, be extended to chemotherapies against other pathogens or cancer.

Investigation of the Influence of Spacer Arm on the Structural Evolution of Affinity Ligands Supported on Agarose

The influence of the spacer arm on the interaction between agarose and a supported ligand was investigated through molecular dynamics for a combination of several spacers. The spacers differ for degree of hydrophobicity, length, and chemical composition, which was varied through insertion of thio, ether, and CH(2) groups. Agarose was modeled through a modified Glycam force field, whose parameters were determined through ab initio calculations. The structural model of agarose used for the calculations was obtained through MD studies of the conformational evolution of several agarose single and double helixes. The simulations showed that a modification of the spacer properties could determine a change of the stable structure of the ligand with respect to the support. In particular, if the spacer is hydrophilic and rigid, the favored structure is with extended spacer and solvated ligand. Either increasing the spacer length, and thus its flexibility, or decreasing its solvation free energy, which corresponds to diminishing its affinity for water, rapidly leads to a conformational change in which the ligand adsorbs on agarose. Interestingly, we found that if the spacer is long and hydrophilic, a third metastable structure, in which the spacer is sandwiched between the ligand and agarose, is possible. Simulations of several ligands adsorbed on neighboring sites on agarose showed that if the support is not held fixed through restraints, the interaction force between vicinal ligands is sufficient to determine a major conformational change of the system.

Essential role of the concentration of immobilized ligands in affinity chromatography: purification of guanidinobenzoatase on an ionized ligand

Guanidinobenzoatase, a plasma protein with possible application as a 'tumor marker', has been fully purified by one-step affinity chromatography. The affinity matrix was prepared by 'controlled' immobilization of an enzyme inhibitor (agmatine) onto commercial agarose gels containing carboxyl moieties activated as N-hydroxysuccinimide esters. In this way, agmatine becomes immobilized through an amido bond and preserves an ionized guanidino moiety. Different matrices with different concentration of ligands were prepared in order to evaluate their properties as affinity supports. Interestingly, matrices with a very low concentration of immobilized ligands (2 microlmol/ml, corresponding to the modification of only 5% of active groups in the commercial resins) exhibited a low capacity for unspecific adsorption of proteins (as anion-exchange resins) and displayed also a high capacity for specific adsorption of our target protein. On the other hand, when affinity matrices possessed a moderate concentration of agmatine (10 micromol/ml of gel or higher), two undesirable phenomena were observed: (a) the matrix behaves as a very good anionic exchange support able to non-specifically adsorb most of plasma proteins and (b) the specific adsorption of our target protein becomes much lower. The latter phenomenon could be due to steric hindrances promoted by the interaction between each individual immobilized ligand and the corresponding binding pocket in the target protein. These hindrances could also be promoted by the presence of a fairly dense layer of immobilized ligands covering the support surface, thus preventing interactions between immobilized ligands and partially buried protein-binding pockets. In this way, a successful affinity purification (23.5% yield, x220 purification factor, a unique electrophoretic band) could be achieved by combination of three approaches: (i) the use of affinity matrices possessing a very low density of immobilized ligands, (ii) performing affinity adsorption at high ionic strength and (iii) performing specific desorption with substrates or substrate analogues.

Effect of accessible immobilized NAD(+) concentration on the bioaffinity chromatographic behavior of NAD(+)-dependent dehydrogenases using the kinetic locking-on strategy

In preparation for studies aimed at establishing the relationship between immobilized NAD(+) concentration and the concentration of soluble locking-on ligand required to promote biospecific adsorption of NAD(+)-dependent dehydrogenases to immobilized NAD(+) derivatives (the "locking-on" strategy), two approaches were evaluated for varying substitution levels: (i) suitable dilution of the affinity matrix with unsubstituted Sepharose 4B and (ii) direct coupling of the required ligand concentration to the inert matrix. The latter approach was found to be the preferable strategy for evaluation of the locking-on tactic because it produced a more homogeneous distribution of immobilized NAD(+) concentration. Affinity chromatographic studies using S(6)-linked NAD(+) derivatives synthesized to various substitution levels showed that the total accessible immobilized NAD(+) concentration has a direct effect on the locking-on behavior of pyridine nucleotide-dependent dehydrogenases. The one-chromatographic-step bioaffinity purification of l-lactate dehydrogenase (L-LDH, EC 1.1.1.27) from bovine heart illustrates the potential of the locking-on strategy for protein purification applications.

Further studies on the bioaffinity chromatography of NAD(+)-dependent dehydrogenases using the locking-on effect

Previous studies have capitalized on ordered kinetic mechanisms in the design of biospecific affinity chromatographic methods for highly efficient purifications and mechanistic studies of enzymes. The most direct tactic has been the use of immobilised analogues of the following, usually enzyme-specific substrates, e.g., lactate/pyruvate in the case of lactate dehydrogenase for which NAD+ is the leading substrate. Such immobilised specific substrates are, however, often difficult or impossible to synthesise. The locking-on strategy reverses the tactic by using the more accessible immobilised leading substrate, immobilised NAD+, as adsorbent with soluble analogues of the enzyme-specific ligands (e.g., lactate in the case of lactate dehydrogenase) providing a substantial reinforcement of biospecific adsorption sufficient to effect adsorptive selection of an enzyme from a group of enzymes such as the NAD(+)-specific enzymes. The value of this approach is demonstrated using model studies with lactate dehydrogenase (LDH, EC 1.1.1.27), alcohol dehydrogenase (ADH, EC 1.1.1.1), glutamate dehydrogenase (GDH, EC 1.4.1.3) and malate dehydrogenase (MDH, EC 1.1.1.37). Purification of bovine liver GDH in high yield from crude extracts is described using the tactic.

Multiple ligand applications in high-performance immunoaffinity chromatography

A mixture of antibodies specific for albumin and transferrin, immobilized onto a single support, was used for the simultaneous extraction of albumin and transferrin from immunoglobulin G by high-performance immunoaffinity chromatography. The affinity column was coupled to a strong cation exchanger in order to monitor the success of the extraction and to demonstrate the compatibility of the two chromatographic modes. Coupling of non-affinity chromatography with multiple ligand affinity chromatography is discussed as an alternative to positive affinity chromatography for protein purification.

Hyaluronidase in ram semen. Quantitative determination, and isolation of multiple forms

A study was made of hyaluronidase in ram semen. The end-group assay conditions used to determine activity quantitatively were chosen to ensure reliability as well as sensitivity [Gacesa, Savitsky, Dodgson & Olavesen (1981) Anal. Biochem. 118, 76-84]; they led to 1 W.H.O. Standard International Hyaluronidase Unit displaying 0.1263 EC munit (1 EC unit of activity releases 1 mumol equivalent of N-acetylglucosamine end groups/min at 37 degrees C). All the activity in the semen was shown to be sperm-derived, and intact spermatozoa were estimated to contain 1.23 EC units per 10(9) cells. In a low-ionic-strength medium, only some 20% of the hyaluronidase was extractable, although up to 80% of the activity could be extracted as the ionic strength was increased; further addition of detergent extracted the remainder. During purification of the enzyme, it was found that inclusion of poly(vinyl alcohol) in the media stabilized the activity; detergent inclusion also improved the yield, especially during early stages. As a consequence both of reliable quantitative determination and of stabilization, a number of forms of hyaluronidase could be isolated in high yield, by using anion-exchange chromatography, cation-exchange chromatography, affinity chromatography and gel filtration. The existence of all these forms was confirmed by electrophoresis and immunoblotting with the use of a monoclonal anti-(ram hyaluronidase) antibody, and their presence in very freshly prepared sperm extracts was demonstrated. The specific activity of the isolated major hyaluronidase form was 15.0 EC units/mg; this was equivalent to 119,000 W.H.O. units/mg, higher than any other previously reported values.

Purification of the fructose 1,6-bisphosphate-dependent lactate dehydrogenase from Streptococcus uberis and an investigation of its existence in different forms

The fructose 1,6-bisphosphate [Fru(1,6)P2]-dependent lactate dehydrogenase in cells of Streptococcus uberis N.C.D.O. 2039 was purified by a procedure that included chromatography on DEAE-cellulose and Blue Sepharose CL-6B in phosphate buffers. The enzyme appeared to interact with Blue Sepharose through NADH-binding sites. The homogeneous enzyme had catalytic properties that were generally similar to those of other Fru(1,6)P2-dependent lactate dehydrogenases, and it had no catalytic activity in the absence of Fru(1,6)P2. Its existence in different forms, depending on conditions, was investigated by ultracentrifugation, analytical gel filtration and activity measurements. It consisted of subunits with Mr 35,900 +/- 500 and, in the presence of adequate concentrations of Fru(1,6)P2, phosphate or NADH, it existed as a tetramer, whereas when these ligands were in lower concentrations or absent, the subunits were in a concentration-dependent association-dissociation equilibrium. Dissociation occurred slowly and inactivated the enzyme, and although added ligands reversed the dissociation, the lost activity was at best only partly restored. An exception occurred when dissociation was caused by a decrease in temperature, in which case the lost activity was fully restored at the original temperature. The tetramer also lost activity at certain ligand concentrations without dissociating. The results together indicated the presence on the enzyme of two classes of binding site for both Fru(1,6)P2 and NADH, and the likelihood that phosphate bound at the same sites as Fru(1,6)P2. Two different ligands together were much more effective at preventing inactivation and dissociation than was expected from their effectiveness when present separately. It was concluded that tetrameric forms of the enzyme rather than the enzyme in association-dissociation equilibrium were involved in the regulation of its activity in vivo.

Comparative affinity chromatography of acetylcholinesterases from five vertebrate species

The efficacy of N-methylacridinium affinity chromatography in the purification of acetylcholinesterases from chicken, rat, calf and human brain and from the electric organ of the electric fish Torpedo marmorata has been investigated. Retention of the enzymes on the N-methylacridinium columns exceeded 90% in all instances except for the chicken enzyme, where 40-80% retention was observed depending on the acridinium concentration. Sucrose density gradient centrifugation profiles revealed no difference between the distribution of molecular forms in the crude extracts and in the partially purified fractions eluted from the columns by decamethonium iodide.

The preparation and properties of folate-binding protein from cow's milk

An improved affinity-chromatographic method for the preparation of folate-binding protein from cow's milk is described. Under dissociating conditions the protein appeared homogeneous in the ultracentrifuge, with a molecular weight of 35 000 +/- 1500, but it was heterogeneous on electrophoresis and ion-exchange chromatography and evidently consisted of several glycoproteins with similar molecular weights that all bound folic acid. Overall, the protein contained a high proportion of half-cystine (18 residues/molecule) and 10.3% of carbohydrate. At saturation it bound approx. 1 mol of folate/mol of protein at pH 7.2. Equilibrium-dialysis measurements of the binding of folic acid and 5-methyltetrahydrofolate to the purified protein gave non-linear Scatchard plots, the shapes of which depended on pH. The results were interpreted in terms of ligand binding to a polymerizing system in which the affinity of ligand for monomer was greater than its affinity for polymer. When the protein concentration was similar to that in cow's milk, dissociation constants (Kd) for folate and 5-methyltetrahydrofolate were 3 nM and 5 nM respectively at pH 7.2 and 37 degrees C, whereas Kd for the binding of folate to monomer was about 50 pM. The properties of the binding protein are discussed in relation to its possible role in folate absorption in the gut.

Purification and some properties of NAD-glycohydrolase from conidia of Neurospora crassa

NAD-glycohydrolase from conidia of Neurospora crassa was purified by affinity chromatography, using 4-methylnicotinamide adenine dinucleotide as ligand immobilized onto Sepharose through a hydrophilic spacer arm. The pure enzyme is a glycoprotein with an isoelectric point of 5.5 and a molecular weight of 33 000 as determined by sodium dodecylsulphate gel electrophoresis. The specific activity is the highest so far found for NAD-glycohydrolases and in various aspects the enzyme is different from that isolated from mycelia of N. crassa grown in a 'zinc-deficient' medium.

Sepharose 4B as a matrix for affinity chromatography. A spin-labelling investigation using nitroxides as model ligands

Nitroxide spin labels were attached to CNBr-activated Sepharose 4B directly and through oligoglycines and oo-amino-carboxylic acids of varying length. The homogeneity of the carbohydrate environments of directly attached labels was investigated by measuring dipolar interactions between nitroxides as a function of solvation and of spin dilution with a diamagnetic analogue, as well as by electron exchange between the nitroxides and paramagnetic metal ions in solution. Only the exchange experiment revealed any inhomogeneity, suggesting that a small proportion of sites may be less accessible than the majority. The distances between sites were sufficiently small to allow, in principle, multiple-site interactions between quite small proteins in solution and immobilized ligands. Reorientation of the label at the matrix, characterized by the correlation time t, became more rapid with increasing spacer length n. For n > 12, the decrease in t was less pronounced. The two types of spacer behaved similarly. Thus an ideal spacer length for affinity separations is 12 atoms; this is in good agreement with data from a variety of affinity separations. The results of electron spin resonance studies of the effect of non-aqueous solvent on directly and indirectly labelled Sepharose 4B were used to suggest reasons why enzymes immobilized on Sepharose may be stabilized to denaturing solvents.

Determination of the interaction of lactate dehydrogenase with high-molecular-weight derivatives of AMP by affinity electrophoresis

The interaction of lactate dehydrogenase with high-molecular-weight derivatives of AMP was studied by affinity electrophoresis in an alkaline buffer system and by means of kinetic measurements. AMP was coupled to synthetic hydroxypropylmethacrylamide copolymers through glycine, 6-aminohexanoic and 12-aminododecanoic spacer arms. The values of the dissociation constants (K) of the lactate dehydrogenase isoenzymes--immobilized AMP complexes determined by affinity electrophoresis decreased with increasing length of the spacer arm. Lactate dehydrogenase was competitively inhibited by high-molecular-weight derivatives of AMP; values of the inhibition constants (Ki) also depended on the spacer arm: the longer the spacer arm the stronger was the interaction between the enzyme and the inhibitor. Ki values for high-molecular weight derivatives of AMP were lower than those obtained for free AMP.

Affinity chromatography of tryptophan synthase from Escherichia coli. Systematic studies with immobilized tryptophanol phosphate

Inhibition studies and affinity chromatography indicate that derivatives of tryptophanol phosphate are suitable ligands for the affinity chromatography of tryptophan synthase. A phenyl group on the spacer arm strengthens the interaction of immobilized tryptophanol phosphate with the enzyme. The alpha 2 beta 2 complex specifically requires the presence of 0.3--0.5 M phosphate ions for binding. The alpha subunit binds in dilute Tris buffer, but its binding is also enhanced by the presence of phosphate ions. The beta 2 subunit binds unspecifically but strongly to the affinity material and to a variety of other immobilized hydrophobic ligands. Binding studies with suspensions of affinity material show that the alpha subunit interacts rapidly and reversibly. Indoleglycerol phosphate and indolepropanol phosphate release bound alpha 2 beta 2 complex and alpha subunit in a competitive manner, indicating that the interaction occurs biospecifically, i.e. via the active site of alpha subunit. L-Serine is a non-competitive inhibitor of binding. These results are discussed with regard to the composite-active-site hypothesis [T. E. Creighton (1970) Eur. J. Biochem, 13, 1--10]. Both the alpha subunit and the alpha 2 beta 2 complex of tryptophan synthase from Escherichia coli can be obtained with high yields and in homogenous form by absorption to the affinity material from partially purified preparations. Elution is achieved with linear gradients either of indolepropanol phosphate or of indoleglycerol phosphate or, in the case of the complex, of L-serine. At the low concentrations of the complex found in crude extracts of wild-type E. coli cells, the unexpectedly high affinity of the beta 2 subunit for hydrophobic ligands leads to partial dissociation of the complex.

Optimisation of conditions for the affinity chromatography of human enterokinase on immobilised p-aminobenzamidine. Improvement of the preparative procedure by inclusion of negative affinity chromatography with glycylglycyl-aniline

The affinity chromatography of human enterokinase using p-aminobenzamidine as the ligand [Grant, D.A.W. & Hermon-Taylor, J. (1976) Biochem. J. 155, 243-254] has been reassessed and the optimal conditions for the synthesis and operation of the derivatised gel defined. Satisfactory adsorbants were only produced using high concentrations of both CNBr and spacer-arm in the initial coupling slurry. Under these conditions it seemed likely that the majority of the ligand in a sterically favourable position to bind enterokinase was on the external surface of the bead. Trypsin binding to the adsorbant was not so critically dependent on the synthetic conditions and correlated closely with the degree of substitution. Dilution of the adsorbant with unlabelled Sepharose 4B indicated that there was more than one binding site per enterokinase molecule. The highest affinity was presumably for the active site, with adsorption supported by secondary interactions with spacer-arm or gel matrix not necessarily on the same bead. Maximal resolution was obtained by prolonged washing of the gel after loading; two populations of intestinal aminopeptidase were identified. Substitution of aniline for p-aminobenzamidine abolished specific enterokinase adsorption and improved the purification procedure by further removal of onon-specifically adsorbed contaminants.

Affinity chromatography on agarose-hexyl-adenosine-5'-phosphate of methionyl-tRNA synthetase from Escherichia coli. Application of the couplings between the methionine and ATP sites

Recent studies by us [Biochemistry (1977) 16, 2570-2579] have shown that L-methioninol, a methionine analog lacking the carboxylate negative charge, enhances the affinity of AMP for methionyl-tRNA synthetase while L-methionine antagonizes the nucleotide binding. Such couplings between ligands of the enzyme have now been applied to affinity chromatography of methionyl-tRNA synthetase on an agarose-hexyl-adenosine-5'-phosphate gel (the spacer is attached to AMP at the adenine C-8 position). Retention of the enzyme on this gel column was shown to be dependent on the presence of appropriate concentrations of magnesium and of L-methioninol in the equilibration buffer. The enzyme was then specifically recovered from the column by omitting the amino alcohol or by adding an excess of L-methionine which antagonizes the cooperative effect of L-methioninol. This approach has provided the basis for a new purification procedure of methionyl-tRNA synthetase which leads to a 200-fold purification in a single chromatographic step. In this manner, after 30-50% ammonium sulfate fractionation of extracts of Escherichia coli EM 20031 (carrying the F32 episome), 0.25 mg X methionyl-tRNA synthetase was obtained at 90% purity per ml of agarose-hexyl-adenosine-5'-phosphate gel.

A new purification procedure for fumarase based of affinity chromatography. Isolation and characterization of pig-liver fumarase

A new procedure has been developed for the isolation of fumarase (EC 4.2.1.2). It is described for the purification of pigheart and liver enzyme. Pyromellitic acid has been covalently coupled to Sepharose-4B with diaminopropanol as spacer arr. When a dialysed 0.55 saturated ammonium sulphate precipitate is applied to the column, in Tris-acetate buffer, pH 7.3, fumarase remains quantitatively bound. It is eluted by competition, together with a few other proteins, by the natural product L-malate. Malate is removed from the eluate by dialysis. After this highly efficient purification step the enzyme is very easily crystallized. The final yield by 67% for both pig heart and liver preparations. The specific activity of fumarase purified from both tissues is found to be the same. Polyacrylamide gel electrophoresis in dodecylsulphate shows one single band corresponding with a subunit molecular weightof 48500. A single band is also obtained by electrophoresis in acid urea. This new procedure based on biospecific affinity chromatography allows a fast and easy preparation of gram quantities of fumarase.

Affinity chromatography and inhibition of chorismate mutase-prephenate dehydrogenase by derivatives of phenylalanine and tyrosine

Several derivatives of phenylalanine and tyrosine were prepared and tested for inhibition of chorismate mutase-prephenate dehydrogenase (EC 1.3.1.12) from Escherichia coli K12 (strain JP 232). The best inhibitors were N-toluene-p-sulphonyl-L-phenylalanine, N-benzenesulphonyl-L-phenylalanine and N-benzloxycarbonyl-L-phenylalanine. Consequently two compounds, N-toluene-sulphonyl-L-p-aminophenylalanine and N-p-aminobenzenesulphonyl-L-phenylalanine, were synthesized for coupling to CNBr-activated Sepharose-4B. The N-toluene-p-sulphonyl-L-p-aminophenylalanine-Sepharose-4B conjugate was shown to bind the enzyme very strongly at pH 7.5. The enzyme was not eluted by various eluents, including 1 M-NaCl, but could be quantitatively recovered by washing with buffer of pH9. Elution was more effective in the presence of 10 mM-1-adamantaneacetic acid, a competitive inhibitor of the enzyme. This affinity-chromatography procedure results in a high degree of purification of the enzyme and can be used to prepare the enzyme in a one-step procedure from the bacterial crude extract. Such a procedure may therefore prove useful in studying this enzyme in a state that closely resembles that in vivo.

The synthesis of several 8-substituted derivatives of adenosine 5'-monophosphate to study the effect of the nature of the spacer arm in affinity chromatography

Reaction of adenosine 5'-monophosphate (Ado-5'-P) with bromine at pH 4.0 yielded 8-bromo-adenosine 5'-monophosphate and following reaction with several alpha,omega-diaminoalkanes gave the corresponding 8-(omega-aminoalkyl)-Ado-5'-P derivatives. Condensation of these analogues with N-trifluoroacetyl-glycine or beta-alanine in the presence of a water-soluble carbodiimide generated several 8-substituted derivatives. These analogues: (see article) comprised an 8-substituted Ado-5'-P ligand to which a spacer molecule of similar length but differing hydrophobicity was attached. The derivatives were purified, characterised and attached to CNBr-activated Sepharose. The chromatographic behaviour of the resulting absorbents was investigated in terms of their ability to bind both lactate and alanine dehydrogenase. The enzymes bound tighter to the more hydrophobic derivatives with the strength of the interaction decreasing with increasing hydropholicity. The effect of the introduction of a single hydroxyl group in the spacer arm was also studied with several enzymes known to exhibit anomalous behavior on affinity chromatography. In free solution, (Ado-5'-P)-8-NH CH2CH2CH2CH2CH2CH2NH2 and (Ado-5'-P)-8-NH CH2-CH CH2NH CO CH2NH2 were competitive with NADH for rabbit muscle lactate dehydrogenase, (see article) with Ki values of 2.0 and 1.8 mM respectively. These data suggest a difference in accessibility of the hydrophobic and hydrophilic derivatives when attached to Sepharose rather than a fundamental difference in affinity. This suggestion is supported by the fact that there is no obvious correlation between the Ki values in free solution of a series of 8-(omega-aminoalkyl)-Ado-5'-P derivatives of increasing chain length, and hence hydrophobicity, and their chromatographic behaviour when immobilised. The data suggest that the hydrophobicity/hydrophilicity of the spacer arm determined the accessibility of the immobilised ligand to interaction with the complementary enzyme.

Heterogeneity of antibodies to adenosine 5'-monophosphate

Antibodies to adenosine 5'-monophosphate were produced in rabbits by injecting a conjugate of the nucleotide (oxidized with periodate) with bovine serum albumin. AMP-specific antibodies were isolated by affinity chromatography. The antiserum was first applied on oligoadenylic acids-agarose column and then the unbound proteins on a morpholine derivative of AMP-agarose column. The antibodies purified on these two columns interact differently with AMP derivatives as shown by immunodiffusion. These results are confirmed by the values of the binding constants of the complexes Fab fragments- AMP and AMP derivatives. The study of Fab fragments -- C(8)-substituted AMP derivatives complexes suggest a syn conformation for the bound nucleotide. Thermodynamic parameters for the Fab fragments-AMP complexes have been determined (deltaHdegrees = --13 kcal/mol and deltaSdegrees = --15 cal - degree-1 - mol-1).

The use of affinity chromatography in purification of cyclic nucleotide receptor proteins

Biospecific affinity chromatography has been used to purify specific cyclic AMP and cyclic GMP receptor proteins. Several variables are important for successful purification of the cyclic AMP receptor protein, the most critical being the length of the aliphatic spacer side arm. 8-(2-Aminoethyl)-amino-cyclic AMP coupled to the aliphatic spacer side arm. 8-(2-Aminoethyl)-amino-cyclic AMP coupled to agarose specifically retains the cyclic AMP receptor protein by interaction with the immobilized nucleotide. Binding of the cyclic AMP receptor subunit of cyclic AMP-dependent protein kinase to the immobilized nucleotide results in dissociation of the catalytic protein phosphokinase subunit which is not retained. The retained cyclic AMP receptor protein is subsequently eluted by cyclic AMP. Homogeneous cyclic AMP receptor protein prepared from rabbit skeletal muscle by affinity chromatography has been characterized. The molecular weight of the native protein as determined by analytical ultracentrifugation and polyacrylamide gel electrophoresis at varying acrylamide concentrations is 76 800 and 82 000, respectively. The protein is asymmetric with frictional and axial ratios of 1.64 and 12. SDS and urea polyacrylamide gel electrophoresis indicate that the native cyclic AMP receptor is composed of two identical subunits of 42 700 molecular weight. The native protein dimer binds 2 moles of cyclic AMP per mole of protein and is active in suppressing activity of isolated catalytic subunits of cyclic AMP-dependent protein kinase. Cyclic GMP receptor protein from bovine lung has been purified using the same affinity chromatography media. Since cyclic nucleotide binding to cyclic GMP-dependent protein kinase does not result in dissociation of regulatory receptor and catalytic phosphotransferase subunits, the cyclic GMP-dependent protein kinase holoenzyme is retained on the column and can be subsequently specifically eluted with cyclic GMP.

Purification of thymidylate synthetase from enzyme-poor sources by affinity chromatography

The adsorption of thymidylate synthetase from Escherichia coli B to aminoalkyl-Sepharose with the increasing length of carbon chain (2--6 carbon atoms) was investigated. A correlation was found between the chain length and adsorption effectiveness, increasing from the two- to the six-carbon chain. A hydrophobic chromatography of the enzyme on aminobutyl-Sepharose gave about 20-fold purification. A new affinity chromatography carrier was synthesized containing tetrahydromethotrexate linked to aminoethyl-Sepharose via its carboxylic groups. The carrier adsorbed the enzyme from the crude preparation only in the presence of deoxyuridine 5'-monophosphate (dUMP) in a concentration of 2 X 10(-5) M. The specifically adsorbed thymidylate synthetase was eluted with sacharose-containing buffers in which dUMP was omitted. The purification procedure was applied to a crude thymidylate synthetase preparation from resting E. coli, calf thymus, Sarcoma 180, and Gardner lymphosarcoma. The purified enzyme from all mentioned sources showed one protein band on disc electrophoresis corresponding to enzymatic activity. The formation of a reversible noncovalent complex enzyme-tetrahydromethotrexate-dUMP on the affinity column is supposed.

Affinity chromatography of acetylcholinesterase. The importance of hydrophobic interactions

An easily prepared affinity column for acetylcholinesterase is described, which may be operated at ionic strength high enough to prevent aggregation of the asymmetric forms of the enzyme. Specific elution by tetraethylammonium or decamethonium was quantitative. The performance of this column is comparable to that of the column described by Dudai and Silman. It is shown that the hexyl 'spacer arm' strongly participates in the enzyme binding and that its replacement with the more hydrophilic spermine chain lowers the affinity. The hexyl chain itself is shown to bind acetylcholinesterase, although with lower affinity and capacity than the complete column. This binding is also partly reversed by inhibitors. Such hydrophobic columns bind the native asymmetric forms of the enzyme more strongly than the lytic globular ones. The aromatic quaternary ligang inhibits Electrophorus but not Torpedo acetylcholinesterase; therefore the column does not retain the Torpedo enzyme. Differences in Km between acetylcholinesterases of the two species also point to differences in their active sites.

Antigen and antibody purification by immunoadsorption: elimination of non-biospecifically bound proteins

Immunoadsorption is a simple and effective method for purifying antigens and antibodies. The major interfering effect is non-biospecific binding, especially when crude preparations of antibodies or antigens are coupled to the matrix. In this paper various possibilities for eliminating these effects are compared and analysed. It was found that for antigen (AFP) purification pre-elution with a pH 10.0 buffer of high ionic strength (1.0 M) is effective. A major problem in purifying antibodies in the non-biospecific binding of IgG. This can be eliminated by using a non-biospecific immunoadsorbent column, where specific antibodies are not, or only weakly bound and IgG with irrelevant specificity but exhibiting high non-biospecific interaction is retained. This has been applied to preparation of sheep anti-pepsinogen II group protease antibodies.

Affinity chromatography of 3 alpha-hydroxysteroid dehydrogenase from Pseudomonas testosteroni. Use of N,N-dimethylformamide to prevent hydrophobic interactions between the enzyme and the ligand

1. The 3alpha-hydroxysteroid: NAD+-oxidoreductase (EC 1.1.1.50) from Pseudomonas testosteroni (ATCC 11996) has been purified by affinity chromatography on Sepharose 4B using glycocholic acid as ligand covalently bound through its carboxyl group to the ethylenediamine spacer. 2. The attachment of the enzyme to the substrate-containing matrix is greatly enhanced by the presence of NAD+ suggesting that this enzyme has a compulsory ordered mechanism where NAD+ binds to the enzyme before the steroid. 3. A NAD+-independent interaction between the enzyme and the ligand was also found. This interaction was mainly hydrophobic and interfered with the NAD+-dependent binding. The NAD+-independent interaction was reduced by N,N-dimethylformamide. 4. By using the affinity column in the presence of 10% N,N-dimethylformamide, highly purified enzyme, as judged from polyacrylamide gel electrophoresis, could be obtained in one step from crude bacterial extracts.

Studies on the use of sepharose-N-(6-aminohexanoyl)-2-amino-2-deoxy-D-glucopyranose for the large-scale purification of hepatic glucokinase

The synthesis of N-(6-aminohexanoyl)-2-amino-2-deoxy-D-glucose is described and it was shown to be a competitive inhibitor (Ki, 0.75 mM) with respect to glucose of rat hepatic glucokinase (EC 2.7.1.2). After attachment to CNBr-activated Sepharose 4B, this derivative was able to remove glucokinase quantitatively from crude liver extracts and release it when the columns were developed with glucose, glucosamine, N-acetyl-glucosamine or KC1. Repeated exposure of the columns to liver extracts led to rapid loss in their effectiveness as affinity matrices because proteins other than glucokinase are bound to the columns. The nature of such protein binding and methods for the rejuvenation of "used" columns are discussed along with the effect of the mode of preparation of the Sepharose-ligand conjugate and the concentration of bound ligand on the purification of glucokinase. Glucose 6-phosphate dehydrogenase is cited as an example of both non-specific protein binding to the affinity column and of the importance of the control of ligand concentration in removing such non-specifically bound proteins. Some guidelines emerged that should be generally applicable to other systems, particularly those which involve affinity chromatography of enzymes that are present in tissue extracts in very low amounts and possess only a relatively low association constant for the immobilized ligand.

Affinity chromatography of thymidine kinase from a rat colon adenocarcinoma

Thymidine kinase from a transplantable colon adenocarcinoma, induced by 1,2-dimethylhydrazine and maintained in CDF rats, was purified by affinity chromatography using thymidine-3'(4-aminophenylphosphate) coupled to carboxyhexyl-Sepharose. Most of the contaminating protein passed through the column; non-specifically adsorbed protein was washed from the column by 0.1 M KC1 in 0.01 M Tris-HC1, 7.5. Thymidine kinase was eluted with 0.1 mM thymidine, 0.1 M KC1 in 0.01 M Tris-HC1, pH 7.5. The purified enzyme accounted for about 26% of the applied activity; the specific activity of the purified material (peak fraction) was 3,500 moles TMP formed per mg protein per 10 min., a 1,800-fold purification of the applied extract. The preparation is free of nucleoside phosphotransferase, but contains other protein impurities. Purification was completed in less than 1 hour, making this a useful procedure for isolation of this unstable enzyme.

The purification and properties of a beta-N-acetylhexosaminidase from Trichomonas foetus

A beta-N-acetylhexosaminidase was purified 800-fold from extracts of Trichomonas foetus by affinity chromatography on a column of N-(epsilon-aminohexanoyl)-2-acetamido-2-deoxy-beta-D-glucopyranosylamine bound to CNBr-activated Sepharose. The enzyme has a dual specificity for the p-nitrophenyl beta-D-glycosides of N-acetylglucosamine and N-acetyl-galactosamine. The parent sugars are both competitive inhibitors. The enzyme has a mol. wt. approx. 150000 and a pH optimum of 6.2. It is suggested that the same active site catalyses both activities and that no part is played by the 4-hydroxyl group in substrate binding, but it is involved in determining the catalytic rate.

Antibodies to adenosine 5'-monophosphate: purification and specificity

Antibodies to adenosine-5'-monophosphate were produced in rabbits by injecting a conjugate of the nucleotide (oxidized with periodate) with bovine serum albumin. Nucleotide-specific antibodies were isolated by affinity chromatography on oligoadenylic acids/agarose column. Pure immunoglobulin G antibodies were obtained by gel filtration on Sephadex G-200. These antibodies, as analyzed by double diffusion react with adenosine 5'-monophosphate--bovine serum albumin, slightly with inosine-5'-monophosphate conjugate and not at all with the other nucleotide conjugates. The association constants for adenosine-5'-monophosphate--antibody complex formation obtained by dialysis equilibrium and fluorescence measurements, are in good agreement. This latter technique was used to study on one hand the influence of temperture and salt on complex formation, on the other hand the interaction of the antibodies with AMP derivatives. The phosphate group, the ribose and the base are recognized by the antibody, but the C-8 atom of adenine residues is not directly involved in the binding.