Affinity chromatography of aminopeptidases

The recent data are generalized concerning a series of synthetic oligopeptides which are competitive inhibitors of aminopeptidases of animal, plant and microbic origin. A method for biospecific chromatography of these enzymes is developed, using as ligands such inhibitors as diazo derivatives of p-aminophenyl-, chloromethyl- and methylketones of L-amino acids and peptides, amino acids, aliphatic acid amides. It is established that the most effective inhibitors of aminopeptidases contain L-amino group in the uncharged form in the N-end position, hydrophobic lateral chain of L-configuration and a carbonyl group analogous to position of these groups in the substrate. Methods for synthesis of certain peptides are developed with respect to the above requirements. It is shown that peptides with a space-inaccessible peptide link and antibiotics are often used as ligands for affinity chromatography of aminopeptidases. At present a nonspecific (ion-exchange, hydrophobic) interaction of sorbent and aminopeptidases is observed, which necessitates to increase the specificity at the stage of the enzyme desorption in the further studies.     

Affinity chromatography of arabinogalactan-proteins

Arabino-(1→3), (1→6)-β-d-galactan-proteins (AGPs) and related compounds from Lolium multiflorum (ryegrass) endosperm cell suspension culture, wheat endosperm, larchwood and Gladiolus stigma extract were shown to bind selectively at neutral pH to a column of Sepharose to which the anti-galactan myeloma protein J539 had been covalently linked, Elution was achieved with buffer at pH 3 or with a pulse of p-nitrophenyl-β-d-galactopyranoside at neutral pH. These observations formed the basis for an affinity chromatographic purification of AGPs from natural sources. Some heterogeneity in a ryegrass AGP preparation was indicated by its incomplete elution by d-galactose.     

Affinity chromatography of nucleases

The review concerns isolation and purification of nucleases by affinity chromatography. Different stationary ligands and the methods for their immobilization on supports are described, along with diverse eluents and various procedures for a nuclease detachment from the affinity sorbents. The data on the affinity chromatography application for measuring the dissociation constants of the enzyme complexes with either immobilized or soluble ligands are compiled.     

Affinity chromatography of neoglycoproteins

Glycoproteins, as a class of biomolecules, exhibit much more heterogeneous structures than non-glycosylated proteins. They present a challenging area of research. Model glycoproteins with well-defined protein and carbohydrate structures are helpful in the search for high-resolution methods for the separation of glycoproteins. Neoglycoproteins, maltose-modified chymotrypsin and lactose-modified chymotrypsin, were synthesised by modifying chymotrypsin with maltose and lactose, respectively, using the reductive amination method. Boronate chromatography was applied to isolate the neoglycoproteins from non-glycosylated substances. The use of Tris–HCl as a shielding reagent during the boronate chromatography proved to be efficient in eliminating unwanted interactions between the boronate ligand and the peptide backbone of chymotrypsin. The retention time of neoglycoproteins on the boronate column was increased with increasing the degree of modification.     

Affinity chromatography of dihydrofolate reductase

1. Dihydrofolate reductase was purified from Lactobacillus casei MTX/R, and studied on affinity columns containing folic acid and methotrexate. Two forms of the enzyme were interconverted by incubation with substrates. 2. Affinity columns were prepared from agarose activated with cyanogen bromide and coupled with 1,6-diaminohexane. Stable folate derivatives were covalently attached by using a carbodi-imide condensation. 3. Columns containing folic acid retarded but did not retain the enzyme. 4. Methotrexate at pH 6.0 was particularly effective for retention of the enzyme. 5. There is selective loss of one form of the enzyme during affinity chromatography in the absence of added NADPH. This loss is due to conversion into a single enzyme form on the column. 6. NADPH has a dual effect in stabilizing the enzyme and in sensitizing it to inactivation by methotrexate, particularly in the presence of glycine. 7. Protein with affinity for methotrexate, but without dihydrofolate reductase activity, may also be eluted from the columns. 8. In a single-step procedure the enzyme was purified nearly 4000-fold from mammalian skin.     

Affinity chromatography of lipoxygenases.

A number of aminohexyl agarose derivatives of unsaturated fatty acids have been prepared and evaluated as materials for the affinity chromatography of soybean and pea lipoxygenases. A practical method for a one-stage purification of soybean lipoxygenase-1, with a purification factor of 16, is described, using either linolenate or docosa-4,7,10,13,16,19-hexaenoate as ligands. Results show that alleged competitive inhibitors do not cause sharp elution from the affinity column, and that there is an increasing specificity of binding and sharpness of elution as the proportion of unsaturation in the ligand is increased. These results are discussed in terms of the relative importance of the types of bonding involved in enzyme-substrate binding.     

Affinity chromatography of creatine kinase

An affinity chromatography technique for purification of creatine kinase is described. Creatine kinase from human skeletal muscle is retained on a column of p-mercuribenzoate-2-aminoethyl-Sepharose. After removal of contaminating proteins with Tris buffer and a solution of p-mercuribenzoate, the creatine kinase is selectively cluted in 80% yield with a gradient of 2-mercaptoethanol. This method yields a highly purified protein with a specific activity of 300 units/mg.     

Affinity chromatography of carbonic anhydrase

An insoluble support for affinity chromatography of carbonic anhydrase has been prepared by coupling Sulfamylon (p-aminomethylbenzene sulfonamide) to Sepharose 4B. Carbonic anhydrase binds to Sulfamylon-Sepharose very strongly and can be eluted under mild conditions by the addition of enzyme inhibitors. The gel was used to purify carbonic anhydrase from human erythrocytes and to separate isozymes B and C. It was also employed to separate native enzyme from modified carbonic anhydrases. The apoenzyme and the carboxymethyl enzyme of human carbonic anhydrase B were both isolated by this method.     

Affinity chromatography of phosphofructokinase.

The behavior of mammalian phosphofructokinase on immobilized adenine nucleotides was investigated. Three different insolubilized ligands were compared using a pure rabbit muscle phosphofructokinase. N⁶-[(6-aminohexyl)-carbamoyl-methyl]-ATP-Sepharose bound at least 90 times more enzyme than either N⁶-(6-aminohexyl)-AMP-agarose or ATP-adipic acid hydrazide-Sepharose. The elution of phosphofructokinase from the ATP-Sepharose with various metabolites and combinations of metabolites was investigated. The enzyme is eluted specifically from N⁶-[(6-aminohexyl)-carbamoyl]-ATP-Sepharose with a mixture of 25 μm each of fructose 6-phosphate and ADP (±Mg²⁺). The enzyme is not eluted either with ATP (25 μm), fructose 1,6-diphosphate (1 mm), ADP (25 μm), fructose 6-phosphate (1 mm) alone, or with a mixture of fructose 1,6-diphosphate (25 μm) and ATP (25 μm). The recovery of bound enzyme was usually greater than 90%. A mixture of glucose 6-phosphate and ADP or a mixture of IDP and fructose 6-phosphate also elutes the enzyme, but the recovery with these eluants was only about 40%. It was concluded that the “dead-end” complex is the most effective in the elution. Using this method, phosphofructokinase has been prepared in an essentially homogeneous form from muscle and brain of rabbit and rat. The overall isolation procedure involves a high speed centrifugation of crude extracts which sediments phosphofructokinase as a pellet, followed with adsorption on N⁶-[(6-aminohexyl)-carbamoyl-methyl]-ATP-Sepharose and specific elution with the mixture of fructose 6-phosphate and ADP.     

Affinity chromatography of cysteine-containing histone.

Affinity chromatography based on the reaction between SH groups in protein and +HgC6H4CO groups in the p-mercuribenzoylaminoethyl derivative of Sepharose 4B was examined with a crude preparation of calf thymus cysteine-containing histone. Adsorption of the histone onto the column by specific coupling was found to be optimal in 0.1 M citrate buffer, pH 5.5, containing 5M urea to prevent any aggregation of histones and their non-specific adsorption onto the column, and elution from the column was successfully performed by cleavage of the resulting S-Hg bond with urea-buffer solution containing 0.05 M 2-mercaptoethanol. Under these conditions both the adsorption and elution were quantitative; no adsorption was observed when either SH-blocked histone or unsubstituted Sepharose was used. The cysteine-containing histone thus recovered, after further purification by Bio-Gel P-60 chromatography to remove some cysteine-containing nonhistone proteins contaminating the starting material, showed a single band on polyacrylamide gel electrophoresis and an amino acid composition agreeing with the known sequence of this histone.     

Affinity chromatography purification of diphtheria toxin

NAD was covalently linked to Sepharose-4B using a 6 carbon spacer. Sterile, dialyzed spent culture medium containing 100 Lf/ml of diphtheria toxin or material concentrated by (NH₄)₂SO₄ precipitation containing 1500 Lf/ml, was chromatographed on a column of NAD–Sepharose. Ultraviolet absorbing material which did not flocculate with diphtheria antitoxin was eluted with 0.02M phosphate buffer. When the elation buffer was changed to one containing 0.5M NaCl, purified toxin was eluted off the column.