Affinity chromatography on immobilised triazine dyes. Studies on the interaction with multinucleotide-dependent enzymes

Biomimetic-dye affinity adsorbents for enzyme purification: application to the one-step purification of Candida boidinii formate dehydrogenase

Formate dehydrogenase (FDH, EC 1.2.1.2) was purified from Candida boidinii cells in a single step by biomimetic-dye affinity chromatography. For this purpose, seven' biomimetic analogues of the monochlorotriazine dye, Cibacron(R) Blue 3GA (CB3GA), and parent dichloro-triazine dye, Vilmafix Blue A-R (VBAR), bearing a car-boxylated structure as their terminal biomimetic moiety, were immobilized on crosslinked agarose gel, Ultrogel A6R. The corresponding new biomimetic-dye adsorbents, along with nonbiomimetic adsorbents bearing CB3GA and VBAR, were evaluated for their ability to purify FDH from extracts obtained after press-disintegration of C. boidinii cells. Optimal conditions for maximizing specific activity of FDH in starting extracts (1.8 U/mg) were realized when cell growth was performed on 4% methanol, and press disintegration proceeded in four consecutive passages before the homogenate was left to stand for 1 h (4 degrees C). When compared to nonbiomimetic adsorbents, biomimetic adsorbents exhibited higher purifying ability. Furthermore, one immobilized biomimetic dye, bearing as its terminal biomimetic moiety mercap-topyruvic acid linked on the chlorotriazine ring (BM6), displayed the highest purifying ability. Adsorption equilibrium data which were obtained for the BM6 adsorbent in a batch system corresponded well to the Langmuir isotherm and, in addition, breakthrough curves were taken for protein and FDH adsorption in a fixed bed of BM6 adsorbent. The dissociation constant ( K(D)) of the complex between immobilized BM6 and FDH was found to equal 0.05 microM. Adsorbent BM6 was employed in the purification of FDH from a 18-L culture of C. boidinii in a single step (60% overall yield of FDH). The purified FDH afforded a single-band on sodium dodecyl sulphate poly-acrylamide gel electrophoresis, and a specific activity of 7,0 U/mg (30 degrees C).

The affinity concept in bioseparation: Evolving paradigms and expanding range of applications

The meaning of the word affinity in the context of protein separation has undergone evolutionary changes over the years. The exploitation of molecular recognition phenomenon is no longer limited to affinity chromatography modes. Affinity based separations today include precipitation, membrane based purification and two-phase/three-phase extractions. Apart from the affinity ligands, which have biological relationship (in vivo) with the target protein, a variety of other ligands are now used in the affinity based separations. These include dyes, chelated metal ions, peptides obtained by phage display technology, combinatorial synthesis, ribosome display methods and by systematic evolution of ligands by exponential enrichment (SELEX). Molecular modeling techniques have also facilitated the designing of biomimetic ligands. Fusion proteins obtained by recombinatorial methods have emerged as a powerful approach in bioseparation. Overexpression in E. coli often result in inactive and insoluble inclusion bodies. A number of interesting approaches are used for simultaneous refolding and purification in such cases. Proteomics also needs affinity chromatography to reduce the complexity of the system before analysis by electrophoresis and mass spectrometry are made. At industrial level, validation, biosafety and process hygiene are also important aspects. This overview looks at these evolving paradigms and various strategies which utilize affinity phenomenon for protein separations.

Affinity chromatography matures as bioinformatic and combinatorial tools develop

Affinity chromatography has the reputation of a more expensive and less robust than other types of liquid chromatography. Furthermore, the technique is considered to stand a modest chance of large-scale purification of proteinaceous pharmaceuticals. This perception is changing because of the pressure for quality protein therapeutics, and the realization that higher returns can be expected when ensuring fewer purification steps and increased product recovery. These developments necessitated a rethinking of the protein purification processes and restored the interest for affinity chromatography. This liquid chromatography technique is designed to offer high specificity, being able to safely guide protein manufactures to successfully cope with the aforementioned challenges. Affinity ligands are distinguished into synthetic and biological. These can be generated by rational design or selected from ligand libraries. Synthetic ligands are generated by three methods. The rational method features the functional approach and the structural template approach. The combinatorial method relies on the selection of ligands from a library of synthetic ligands synthesized randomly. The combined method employs both methods, that is, the ligand is selected from an intentionally biased library based on a rationally designed ligand. Biological ligands are selected by employing high-throughput biological techniques, e.g. phage- and ribosome-display for peptide and microprotein ligands, in addition to SELEX for oligonucleotide ligands. Synthetic mimodyes and chimaeric dye-ligands are usually designed by rational approaches and comprise a chloro-triazinlyl scaffold. The latter substituted with various amino acids, carbocyclic, and heterocyclic groups, generates libraries from which synthetic ligands can be selected. A 'lead' compound may help to generating a 'focused' or 'biased' library. This can be designed by various approaches, e.g.: (i) using a natural ligand-protein complex as a template; (ii) applying the principle of complementarity to exposed residues of the protein structure; and (iii) mimicking directly a natural biological recognition interaction. Affinity ligands, based on the peptide structure, can be peptides, peptide-mimetic derivatives (<30 monomers) and microproteins (e.g. 25-200 monomers). Microprotein ligands are selected from biological libraries constructed of variegated protein domains, e.g. minibody, Kunitz, tendamist, cellulose-binding domain, scFv, Cytb562, zinc-finger, SpA-analogue (Z-domain).

Evaluation and applications of a new dye affinity adsorbent

The basic properties of a new dye affinity adsorbent Toyopearl AF-Blue HC-650M and its applications to the purification of proteins were studied. The binding capacity for human serum albumin (HSA) was greater than 18 mg per ml gel. The dye leakage from Toyopearl AF-Blue HC-650M in 0.5 M NaOH and 0.5 M HCI was less compared with an agarose adsorbent. Caustic stability study also demonstrated this material withstood exposure to 0.1 M NaOH for 1 month with no significant loss of binding capacity for HSA. We purified human albumin from human serum and lactate dehydrogenase (LDH) from rabbit muscle extract in a single step. Sodium dodecylsulfate-polyacrylamide gel electrophoresis indicates that human albumin and LDH were highly purified.

Dye-ligand affinity systems

Dye-ligands have been considered as one of the important alternatives to natural counterparts for specific affinity chromatography. Dye-ligands are able to bind most types of proteins, in some cases in a remarkably specific manner. They are commercially available, inexpensive, and can easily be immobilized, especially on matrices bearing hydroxyl groups. Although dyes are all synthetic in nature, they are still classified as affinity ligands because they interact with the active sites of many proteins mimicking the structure of the substrates, cofactors, or binding agents for those proteins. A number of textile dyes, known as reactive dyes, have been used for protein purification. Most of these reactive dyes consist of a chromophore (either azo dyes, anthraquinone, or phathalocyanine), linked to a reactive group (often a mono- or dichlorotriazine ring). The interaction between the dye ligand and proteins can be by complex combination of electrostatic, hydrophobic, hydrogen bonding. Selection of the supporting matrix is the first important consideration in dye-affinity systems. There are several methods for immobilization of dye molecules onto the support matrix, in which usually several intermediate steps are followed. Both the adsorption and elution steps should carefully be optimized/designed for a successful separation. Dye-affinity systems in the form of spherical sorbents or as affinity membranes have been used in protein separation.

Biomimetic dyes as affinity chromatography tools in enzyme purification

Affinity adsorbents based on immobilized triazine dyes offer important advantages circumventing many of the problems associated with biological ligands. The main drawback of dyes is their moderate selectivity for proteins. Rational attempts to tackle this problem are realized through the biomimetic dye concept according to which new dyes, the biomimetic dyes, are designed to mimic natural ligands. Biomimetic dyes are expected to exhibit increased affinity and purifying ability for the targeted proteins. Biocomputing offers a powerful approach to biomimetic ligand design. The successful exploitation of contemporary computational techniques in molecular design requires the knowledge of the three-dimensional structure of the target protein, or at least, the amino acid sequence of the target protein and the three-dimensional structure of a highly homologous protein. From such information one can then design, on a graphics workstation, the model of the protein and also a number of suitable synthetic ligands which mimic natural biological ligands of the protein. There are several examples of enzyme purifications (trypsin, urokinase, kallikrein, alkaline phosphatase, malate dehydrogenase, formate dehydrogenase, oxaloacetate decarboxylase and lactate dehydrogenase) where synthetic biomimetic dyes have been used successfully as affinity chromatography tools.

Molecular modeling for the design of a biomimetic chimeric ligand. Application to the purification of bovine heart L-lactate dehydrogenase

Molecular modeling was employed for the design of a biomimetic chimeric ligand for L-lactate dehydrogenase (LDH). This ligand is an anthraquinone monochlorotriazinyl dye comprising two moieties: (a) the ketocarboxyl biomimetic moiety, 2-(4-aminophenyl)-ethyloxamic acid, linked on the monochlorotriazine ring, mimicking the natural substrate of LDH, and (b) the anthraquinone chromophore moiety, linked also on the same monochlorotriazine ring via a diaminobenzenesulfonate group, acting as pseudomimetic of the cofactor NAD+. The positioning of the dye in the enzyme's binding site is primarily achieved by the recognition and positioning of the pseudomimetic anthraquinone moiety. The positioning of the biomimetic ketocarboxylic moiety is based on a match between the polar and hydrophobic regions of the enzyme's binding site with those of the biomimetic moiety of the ligand. The length of the biomimetic moiety is predetermined for the ketoacid to approach the enzyme catalytic site and form charge-charge interactions. The biomimetic chimeric ligand and the commercial nonbiomimetic ligand Cibacron(R) blue 3GA (CB3GA), were immobilized on crosslinked beaded agarose gel via their chlorotriazine ring. The two affinity adsorbents were evaluated for their purifying ability for LDH from six sources (bovine heart and pancreas, porcine muscle, chicken liver and muscle, and pea seeds). The biomimetic adsorbent exhibited approximately twofold higher purifying ability for LDH compared to the CB3GA adsorbent; therefore, the former was integrated in the purification procedure of LDH from bovine heart extract. The LDH afforded by this two-step purification procedure shows specific activity equal to 600 U/mg (25 degrees C) and a single band after SDS-PAGE analysis.

Oxalate oxidase from barley roots: purification to homogeneity and study of some molecular, catalytic, and binding properties

Oxalate oxidase (OXO) was purified to homogeneity in three steps from roots of barley seedlings. The purification method comprised: (i) thermal treatment (60 degrees C, 10 min), (ii) affinity chromatography on immobilized either Procion turquoise MX-G dye or biomimetic aminoethyl oxamic blue dye, and (iii) affinity chromatography on immobilized lectin concanavalin A (overall performance: 1096-fold purification, 42% recovery). The purified enzyme has a specific activity of 34 U mg-1 (25 degrees C), and is a homopentamer of M(r) approximately 125,000 (HPLC analysis) showing a single band on SDS-polyacryl-amide gel electrophoresis (M(r) approximately 26,000) after staining with silver nitrate. The kinetic constants of the purified enzyme for oxalate are K(m) 0.27 mM and kcat 22 s-1 (37 degrees C), whereas at [oxalate] > or = 4 mM the enzyme exhibited substrate inhibition. Barley root OXO contains no prosthetic group absorbing at 370 or 450 nm, and riboflavin and FAD have no effect on its activity. The enzyme is activated by 1 mM each of Ca2+ (1.7-fold) and Pb2+ (2.6-fold). Irreversible inactivation studies with denatured (70 degrees C) and native (37 degrees C) enzyme using the sulfhydryl-attacking reagent 5,5-dithiobis(2-nitrobenzoic) acid (1.4 mM), in the presence and absence of SDS, respectively, have shown that denatured OXO (4% SDS, 10 min, 100 degrees C) exhibited 10 HS groups per molecule, whereas native OXO displayed one accessible HS group per molecule after approximately 15 min incubation and, over the same period, maintained its catalytic activity to 90%. Furthermore, native OXO treated with beta-mercaptoethanol (1 mM) lost 83% of its catalytic activity within 5 min. These findings indicate that some cysteines may preserve the catalytic activity of OXO by maintaining the integrity of its tertiary structure via disulfide bond formation.

Molecular modelling for the design of chimaeric biomimetic dye-ligands and their interaction with bovine heart mitochondrial malate dehydrogenase

Molecular modelling and kinetic inhibition studies, as well as KD determinations by both difference-spectra and enzyme-inactivation studies, were employed to assess the ability of purpose-designed chimaeric biomimetic dyes (BM dyes) to act as affinity ligands for bovine heart L-malate dehydrogenase (MDH). Each BM dye was composed of two enzyme-recognition moieties. The terminal biomimetic moiety bore a carboxyl or a keto acid structure linked to the triazine ring, thus mimicking the substrate of MDH. The chromophore anthraquinone moiety remained unchanged and the same as that of the parent dye Vilmafix Blue A-R (VBAR), recognizing the nucleotide-binding site of MDH. The monochlorotriazine BM dyes did not inactivate MDH but competitively inhibited inactivation by the parent dichlorotriazine dye VBAR. Dye binding to MDH was accompanied by a characteristic spectral change in the range 500-850 nm. This phenomenon was reversed after titration with increasing amounts of NADH. When compared with VBAR, Cibacron Blue 3GA and two control non-biomimetic anthraquinone dyes, all BM dyes exhibited lower KD values and therefore higher affinity for MDH. The enzyme bound preferably to BM ligands substituted with a biomimetic aromatic moiety bearing an alpha-keto acid group and an amide linkage, rather than a monocarboxyl group. Thus the biomimetic dye bearing p-aminobenzyloxanilic acid as its terminal biomimetic moiety (BM5) exhibited the highest affinity (KD 1.3 microM, which corresponded to a 219-fold decrease over the KD of a control dye). BM5 displayed competitive inhibition with respect to both NADH (Ki 2.7 microM) and oxaloacetate (Ki 9.6 microM). A combination of molecular modelling and experimental studies has led to certain conclusions. The positioning of the dye in the enzyme is primarily achieved by the recognition and positioning of the nucleotide-pseudomimetic anthraquinone moiety. The hydrophobic groups of the dye provide the driving force for positioning of the ketocarboxyl biomimetic moiety. A match between the alternating polar and hydrophobic regions of the enzyme binding site with those of the biomimetic moiety is desirable. The length of the biomimetic moiety should be conserved in order for the keto acid to approach the enzyme active site and form charge-charge interactions.

Dye-affinity labelling of bovine heart mitochondrial malate dehydrogenase and study of the NADH-binding site

The ability of the reactive dichlorotriazine dye Vilmafix Blue A-R (VBAR) to act as an affinity label for bovine heart L-malate dehydrogenase (MDH) was studied. VBAR binds specifically and irreversibly to MDH (k3 0.16 min-1; KD 14.4 microM). The inactivation of the NADH-dependent enzyme by VBAR is competitively inhibited by NAD+, NADH and ADP. Quantitatively inhibited MDH contained approx. 1 mol of dye per mol of active site. The inhibition is irreversible and activity cannot be recovered either on incubation with 10 mM NAD+, 10 mM NADH or 10 mM ADP, or by extensive dialysis or gel-filtration chromatography. Data obtained from high-performance gel-filtration chromatography and analysed by Scatchard plot suggested the presence of two coenzyme-binding sites per MDH dimer. Tryptic digestion of VBAR-labelled MDH followed by reverse-phase HPLC analysis revealed one VBAR-labelled peptide. It appears that each subunit features the same peptide bearing the modifying residue involved in MDH labelling. The pKa of the modifying residue is 8.05. Both total acid hydrolysis of VBAR-labelled MDH followed by HPLC and TLC analysis, and molecular-modelling studies suggest that the modifying residue is Lys-81 and/or Lys-217.

Reversible and irreversible inhibition of sheep liver sorbitol dehydrogenase with Cibacron Blue 3GA and Eriochrome Black T

Due to the central role of sorbitol dehydrogenase in diabetic cataract, it is important to examine this enzyme's interaction with different inhibitory compounds such as dyes. The aim of the study was to investigate the binding of Cibacron Blue and Eriochrome Black T to the active site in sorbitol dehydrogenase. These dyes' effect on the enzyme was studied by steady state and affinity labelling kinetics. Both dyes were coenzyme competitive inhibitors with KEI values around 0.5 microM. Essentially the same KEI values were obtained using the dyes as protecting ligands against the affinity label D,L-alpha-Bromo-beta-(5-imidazolyl)-propionic acid. Both dyes were also able to inhibit the enzyme irreversibly through an affinity labelling mechanism, with KEI' values for Cibacron Blue and Eriochrome Black T of 2.2 and 3.1 mM, respectively. Dithiothreitol and NADH were competitive protecting ligands against both dyes. The rate of inactivation was fastest for Cibacron Blue at acid pH values, while the opposite was the case with EBT. Both Cibacron Blue and Eriochrome Black T bind to sorbitol dehydrogenase in two different ways. In both cases the complex formed prior to irreversible inhibition is the weakest. The tighter reversible complexes are suggested to share a common epitope in the coenzyme binding region. Both irreversible complexes involve binding close to the zinc ion at the active site and the sugar binding site. Due to different pH dependences it can be concluded that the affinity labelling mechanism is different for the two dyes and in neither case is the inactivation due to removal of the active site zinc ion.

Biomimetic dye affinity chromatography for the purification of bovine heart lactate dehydrogenase

Three biomimetic dye ligands bearing as a triazine-linked terminal moiety a carboxylated structure, which mimics substrates and inhibitors of L-lactate dehydrogenase (LDH), were immobilized on cross-linked agarose Ultrogel A6R. These biomimetic dyes are purpose-designed analogues of commercial monochlorotriazine Cibacron Blue 3GA (CB3GA) and parent dichlorotriazine Vilmafix Blue A-R (VBAR). The corresponding biomimetic adsorbents, along with non-biomimetic adsorbents bearing CB3GA and VBAR, were evaluated for their ability to purify LDH from bovine heart crude extract. When compared with non-biomimetic adsorbents, all biomimetic adsorbents exhibited a higher purifying ability. Further, one immobilized biomimetic dye, bearing mercaptopyruvic acid as biomimetic moiety, displayed the highest purifying ability. The concentration of immobilized dye affected both the capacity and the purifying ability of the affinity column, exhibiting an optimum value 2.2 mumol dye/g moist gel. This affinity adsorbent was exploited for the purification of LDH from bovine heart in a two-step procedure. The procedure consisted in a biomimetic dye affinity chromatography step (NAD+/sulphite elution, 25-fold purification, 64% step yield), followed by DEAE-agarose ion-exchange chromatography (1.4-fold purification, 78% step yield). The purified enzyme exhibited a specific activity of ca. 480 u/mg at 25 degrees C (content of impurities: pyruvate kinase and glutamic-oxaloacetic transaminase were not detected; malate dehydrogenase, 0.01%), compared with ca. 250 u/mg of commercial bovine heart LDH (malate dehydrogenase, 0.05%) suitable for analytical purposes.

Affinity labeling of recombinant ricin A chain with Procion blue MX-R

Recombinant ricin A chain was irreversibly modified by Procion blue MX-R, a dichlorotriazinyl analogue of Cibacron blue F3G-A, at pH 7.5 and 4 degrees C in 90 h with over 95% loss of activity in an in vitro translation assay. The presence of total yeast RNA reduced the covalent attachment of Procion blue MX-R to ricin A chain. Quantitatively modified ricin A chain contained 2 mol Procion blue MX-R/mol 29-kDa subunit. Tryptic digestion and resolution of the peptides by reverse-phase high-performance liquid chromatography yields a blue peptide corresponding to Gln5-Arg26 of ricin A chain. Thus, a likely dye-binding site on recombinant ricin A was identified. This region is removed from the active-site cleft of recombinant ricin A but may be involved in its substrate binding.

Chromatography in the downstream processing of biotechnological products

Chromatography techniques are essential for the isolation and purification of most of the high value products of modern biotechnology. The economically sensible and technically satisfactory downstream processing of a therapeutic protein, usually involves a number of chromatographic steps. Its development and optimization require considerable knowledge of the various physico-chemical and engineering aspects of biochemical chromatography. This review addresses the various modes of chromatography and the design of chromatographic separation processes from a biotechnologist's point of view. Strategies for optimizing the structure of the downstream process are outlined and scaling up consideration are discussed. The importance of the different chromatographic methods in research and development is estimated in an analysis of protein purification schemes recently published in the literature. Finally, examples of the application of chromatographic procedures for process scale product purification in the biotechnological industry are given.

Rapid purification of native SecA from Escherichia coli: development of a new affinity chromatography procedure

The SecA protein occupies a pivotal position in the public protein export pathway in Escherichia coli. The multifunctional SecA protein recognizes cytoplasmic factors associated with export including the presecretory protein and targets the complex to the inner membrane, where it acts in the early stages of protein translocation. The ability of SecA to bind ATP was the basis for the development of a novel, rapid purification scheme involving a single chromatographic step. Affinity chromatography was carried out on Red Sepharose CL-6B. The SecA present in crude extracts of E. coli binds strongly to this dye-ligand matrix, and active protein was purified to greater than 90% homogeneity. The protein isolated by this procedure retained the previously described ATPase and RNA-binding activities of SecA. This approach should permit the rapid purification of SecA homologs from a variety microorganisms.

Toxicity studies on native Procion Red HE-3B and released dye from affinity material exposed to degradative chemical conditions

Leached ligands from chromatographic packing material submitted to drastic regeneration conditions can contaminate pure biological preparations. These contaminants could have adverse effects from a toxicology point of view that are very poorly documented in liquid chromatography for protein separation. Investigations on toxicity level have been made on released material from immobilized Procion Red HE-3B, after formal identification of the nature of the leached chemical material. Toxicity investigations in vitro involved a number of tests on living cells (eucaryotic and procaryotic) covering different aspects. Behaviour of cells in regular cultures, polyploïdia induction, genotoxicity as well as mechanisms of endocytosis have been studied. Results showed no toxic effects within the range of concentration of dye and dye derivatives studied. Genotoxicity studies in particular did not show any toxic effect over a range of concentration much higher than the regular level of dye leakage from the sorbent.

The affinity technology in downstream processing

The quality criteria imposed on several biochemicals are stringent, thus, high-separation purification technology is important to downstream processing. Affinity-based purification technologies are regarded as the finest available, and each one differs in its purifying ability, economy, processing speed and capacity. The most widely used affinity technology is classical affinity chromatography, however, other chromatography-based approaches have also been developed, for example, perfusion affinity chromatography, hyperdiffusion affinity chromatography, high-performance affinity chromatography, centrifugal affinity chromatography, affinity repulsion chromatography, heterobifunctional ligand affinity chromatography and the various chromatographic applications of 'affinity tails'. On the other hand, non-chromatographic affinity technologies aim at high throughput and seek to circumvent problems associated with diffusion limitations experienced with most chromatographic packings. Continuous affinity recycle extraction, aqueous two-phase affinity partitioning, membrane affinity filtration, affinity cross-flow ultrafiltration, reversible soluble affinity polymer separation and affinity precipitation are all non-chromatographic technologies. Several types of affinity ligands are used to different extents; antibodies and their fragments, receptors and their binding substances, avidin/biotin systems, textile and biomimetic dyes, (oligo)peptides, antisense peptides, chelated metal cations, lectins and phenylboronates, protein A and G, calmodulin, DNA, sequence-specific DNA, (oligo)nucleotides and heparin. Likewise, there are several support types developed and used; natural, synthetic, inorganic and composite materials.

Protein purification by dye-ligand chromatography

Dye-ligand chromatography has developed into an important method for large-scale purification of proteins. The utility of the reactive dyes as affinity ligands results from their unique chemistry, which confers both the ability to interact with a large number of proteins as well as easy immobilization on typical adsorbent matrices. Reactive dyes can bind proteins either by specific interactions at the protein's active site or by a range of non-specific interactions. Divalent metals participate in yet another type of protein-reactive dye interactions which involve the formation of a ternary complex. All of these types of interactions have been exploited in schemes for protein purification. Many factors contribute to the successful operation of a dye-ligand chromatography process. These include adsorbent properties, such as matrix type and ligand concentration, the buffer conditions employed in the adsorption and elution stages, and contacting parameters like flowrate and column geometry. Dye-ligand chromatography has been demonstrated to be suitable for large-scale protein purification due to their high selectivity, stability, and economy. Also, the issue of dye leakage and process validation of large-scale dye-ligand chromatography has been discussed. Reactive dyes have also been applied in high performance liquid affinity chromatographic techniques for protein purification, as well as non-chromatographic techniques including affinity partition, affinity membrane separations, affinity cross-flow filtration, and affinity precipitation.

Immunochemical quantification of procion red HE-3B used as ligand in affinity chromatography

The quantification of Procion Red HE-3B used as a ligand in affinity chromatography for proteins is reported. It's based on an enzyme-linked immunosorbent assay using antibodies against the dye. Polyclonal antibodies were classically prepared after conjugation of the dye on KLH and injection into rabbits. The development of the assay was based on the competitive inhibition between hemoglobin-dye complex and free dye. The sensitivity of this method was about 1000-times higher than a classical spectrophotometric assay, and was modulated by some chemical substituents attached on the native dye. It was demonstrated that the assay was applicable to the determination of dye traces that may be released from dye affinity sorbents. Moreover, the quantification of the dye was successfully applied to proteins that are being purified from a dye affinity column.

The applications of reactive dyes in enzyme and protein downstream processing

Downstream processing of proteins is often a key factor in the overall process of satisfying product specifications and meeting current commercial demands. In this context, affinity chromatography and other techniques based on the affinity concept have revolutionized protein purification technology, although they have failed to demonstrate their broader applicability at the process scale. On the other hand, reactive dyes offer many advantages as pseudoaffinity media and in many occasions have successfully circumvented problems associated with conventional affinity ligands. The main features of reactive dyes include their broad spectrum of interaction with proteins, low cost, ready availability, high reactivity, ease of immobilization, and both biological and chemical stability. Consequently, dye-ligand media now find application in both analytical and process-scale purification of proteins by techniques such as low- and high-pressure performance affinity chromatography, affinity partitioning, and affinity precipitation.

Dye-ligand chromatography for the resolution and purification of restriction endonucleases

The resolution of restriction endonucleases from the same microorganism is conventionally achieved by lengthy fractionation protocols. We now report effective single-step procedures that exploit dye-ligand chromatography for the resolution and purification of restriction enzymes. After suitable initial screening, we demonstrated that resolution of two restriction activities can be achieved in one chromatographic step, and further purification can subsequently be effected using selected dye-adsorbents. Accordingly, we resolved in one step, Hpa I from Hpa II, Hind II from Hind III, and Sac I from Sac II. Furthermore, a three-step chromatographic procedure has been developed to purify EcoRV suitable for commercial exploitation, as judged by the "overdigestion" and "cut-ligate-recut" quality control tests.

Purification of IMP dehydrogenase from rat hepatoma 3924A

IMP dehydrogenase (EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis and a promising target for cancer chemotherapy, was purified 4860-fold to homogeneity from rat hepatoma 3924A by a method including affinity chromatography in which IMP is bound to epoxy-activated Sepharose 6B. This affinity gel provided a specific elution of the enzyme with 0.5 mM IMP. The final enzyme preparation gave a single band with a molecular weight of 60,000 +/- 1000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis.

High-performance liquid chromatography for the purification of restriction endonucleases, application to BanII, SacI, and SphI

Conventional fractionation methods are time consuming, thus they prolong the time required to process low-stability restriction enzymes. We now report a rapid and effective two-step chromatographic method that affords high purity endonucleases in a short time. Accordingly, an inexpensive chromatographic adsorbent such as phosphocellulose or dyed agarose in the first step is coupled to a high-performance ion exchanger, namely, MonoQ, in the second step. The purification schemes reported here are now in routine use to prepare high-purity BanII, SacI, and SphI as judged by the "overdigestion" and "cut-ligate-recut" stringent quality tests.

Affinity and hydrophobic chromatography of Escherichia coli aspartate transcarbamoylase

Chromatography of aspartate transcarbamoylase from Escherichia coli on agarose-immobilized dyes and alkyl-agaroses of differing carbon length were investigated. The bacterial aspartate transcarbamoylase was bound by Procoin red HE3B-agarose and Cibacron blue F3GA-agarose nearly completely under the conditions chosen relative to other agarose-coupled dyes. The aspartate transcarbamoylase holoenzyme was eluted from the Procion red HE3B-agarose slightly later than from the Cibacron blue F3GA-agarose during salt gradient elution. The catalytic trimer of the enzyme as well as its regulatory dimer were eluted by a lower salt concentration from both dye-agarose gels than the concentration required to elute the holoenzyme. The interaction of the catalytic trimer with the Procion red HE3B-agarose and Cibacron blue F3GA-agarose gels may be a determinant in the holoenzyme being retained on these resins. Of those alkyl-agaroses tested, the ethyl-, propyl- and hexyl-agarose gels bound the majority of aspartate transcarbamoylase activity. Chromatography of aspartate transcarbamoylase on ethyl-agarose found it to be eluted by a low salt concentration. A purification scheme for relatively small amounts of aspartate transcarbamoylase utilizing Procion red HE3B-agarose and ethyl-agarose is presented. This purification scheme is particularly useful for mutant versions of aspartate transcarbamoylase which cannot be purified by literature procedures.

Purification and properties of inosine monophosphate oxidoreductase from nitrogen-fixing nodules of cowpea (Vigna unguiculata L. Walp)

Using ammonium sulfate precipitation, gel filtration, and affinity chromatography, inosine monophosphate (IMP) oxidoreductase (EC 1.2.1.14) was isolated from the soluble proteins of the plant cell fraction of nitrogen-fixing nodules of cowpea (Vigna unguiculata L. Walp). The enzyme, purified more than 140-fold with a yield of 11%, was stabilized with glycerol and required a sulfydryl-reducing agent for maximum activity. Gel filtration indicated a molecular weight of 200,000, and sodium dodecyl sulfate-gel electrophoresis a single subunit of 50,000 Da. The final specific activity ranged from 1.1 to 1.5 mumol min-1 mg protein-1. The enzyme had an alkaline pH optimum and showed a high affinity for IMP (Km = 9.1 X 10(-6) M at pH 8.8 and NAD levels above 0.25 mM) and NAD (Km = 18-35 X 10(-6) M at pH 8.8). NAD was the preferred coenzyme, with NADP reduction less than 10% of that with NAD, while molecular oxygen did not serve as an electron acceptor. Intermediates of ureide metabolism (allantoin, allantoic acid, uric acid, inosine, xanthosine, and XMP) did not affect the enzyme, while AMP, GMP, and NADH were inhibitors. GMP inhibition was competitive with a Ki = 60 X 10(-6) M. The purified enzyme was activated by K+ (Km = 1.6 X 10(-3) M) but not by NH+4. The K+ activation was competitively inhibited by Mg2+. The significance of the properties of IMP oxidoreductase for regulation of ureide biosynthesis in legume root nodules is discussed.

Studies on the nature and activation of O2(-)-forming NADPH oxidase of leukocytes. Identification of a phosphorylated component of the active enzyme

Highly active superoxide (O2-)-forming NADPH oxidase was extracted from plasmamembranes of phorbol-12-myristate-13-acetate-activated pig neutrophils and was partially purified by gel filtration chromatography. Oxidase activity copurified with cytochrome b-245 in an aggregate containing phospholipids and was almost completely separated from FAD and NAD(P)H-cytochrome c reductase. A polypeptide with molecular weight of 31,500 strictly paralleled the purification of NADPH oxidase, suggesting that it is a major component of the enzyme. The enzyme complex was then dissociated by high detergent and salt concentration and cytochrome b-245 was isolated by a further gel filtration chromatography, with a 147 fold purification with respect to the initial preparation. The cytochrome b-245 showed a 31,500 molecular weight by SDS electrophoresis, indicating that it is actually the component previously identified in the partially purified enzyme. The 31,500 protein was phosphorylated in enzyme preparations from activated but not from resting neutrophils, suggesting that phosphorylation of cytochrome b-245 is involved in the activation mechanism of the O2(-) -forming enzyme responsible for the respiratory burst in phagocytes.

Dye-ligand affinity chromatography: the interaction of Cibacron Blue F3GA with proteins and enzymes

The dye Cibacron Blue F3GA has a high affinity for many proteins and enzymes. It has therefore been attached to various solid supports such as Sephadex, Sepharose, polyacrylamide, and the like. In the immobilized form the dye has rapidly been exploited as an affinity chromatographic medium to separate and purify a variety of proteins including dehydrogenases, kinases, serum albumin, interferons, several plasma proteins, and a host of other proteins. Such a diversity shown by the blue dye in binding several unrelated classes of proteins has generated considerable work in terms of studies of the chromophore itself and also the immobilized ligand. As a prelude to realizing the full potential of the immobilized Cibacron Blue F3GA, an understanding of the basic interactions of the dye with its surroundings must be gained. It has been recognized that the dye is capable of hydrophobic and/or electrostatic interactions at the instance of the ambient conditions. The study of interactions of the dye with salts, solvents, and other small molecules indicates the nature of the interactions of the dye with different kinds of groups at the interacting sites of proteins. The review will cover such interactions of the dye with the proteins, the interactions of the proteins with the immobilized ligand, and the media used to elute the bound protein in several cases, and thus consolidate the available information on such studies into a cogent and comprehensive explanation.

Purification of hydrogenases by affinity chromatography on Procion Red-agarose

The agarose-coupled triazine dye Procion Red HE-3B has been demonstrated to be applicable as an affinity gel for the purification of five diverse hydrogenases, namely the soluble, NAD-specific and the membrane-bound hydrogenase of Alcaligenes eutrophus, the membrane-bound hydrogenase of the N2-fixing Alcaligenes latus, the reversible H2-evolving and the unidirectional H2-oxidizing hydrogenase of Clostridium pasteurianum. In the case of the soluble hydrogenase of A. eutrophus, chromatography on Procion Red-agarose even permitted the separation of inactive from active enzyme, thus yielding a 2-3-fold increase in specific activity. For the homogeneous enzyme preparation obtained after two column steps (Procion Red-agarose, DEAE-Sephacel), a specific activity of 121 mumol of H2 oxidized/min per mg of protein was determined. Kinetic studies with free Procion Red provided evidence that the diverse hydrogenases are competitively inhibited by the dye, each with respect to the electron carrier (NAD, Methylene Blue, Methyl Viologen), indicating a specific interaction between Procion Red and the catalytic centres of the enzymes. For the highly purified preparations of the soluble and the membrane-bound hydrogenase of A. eutrophus, in 50 mM-potassium phosphate, pH 7.0, Ki values for Procion Red of 103 and 19 microM have been determined.

Metal ion-promoted binding of proteins to immobilized triazine dye affinity adsorbents

Low concentrations of metal ions, particularly those of the first row transition series such as Zn2+, Co2+, Mn2+, Ni2+, Cu2+, and, to a lesser extent, the group IIA ions, Ca2+ and Mg2+, promotes binding of carboxypeptidase G2, alkaline phosphatase and yeast hexokinase to immobilized Procion Red H-8BN, Procion Yellow H-A and Cibacron Blue F3G-A respectively. The binding of ovalbumin to immobilized Cibacron Blue F3G-A and Procion Orange MX-G is selectively enhanced in the presence of AI3+. With ovalbumin and alkaline phosphatase, the effect is almost totally specific for both the metal ion and dye, whereas with carboxypeptidase G2 and hexokinase, metal ions such as Co2+, Ni2+, Mn2+, Cu2+, Ca2+ and Mg2+ also promote binding to varying degrees. Almost all other monovalent and trivalent metal ions appear to be ineffective. Metal ion-bound enzymes can subsequently be eluted with appropriate chelating agents of the amine, aminocarboxylate or substituted pyridine classes.