Studies of the distribution of proteins bound to CNBr-activated Sepharose 6B at the electron-microscopic level

Preparation of cell-affinity adsorbents by immobilization of peptides to Sephadex G-10

In this study, affinity adsorbents for the binding of activated blood platelets and endothelial cells were prepared from Sephadex G-10 by immobilization of peptides, derived from the cell-adhesive amino acid sequence RGD (arginine-glycine-aspartic acid). Derivatization of Sephadex G-10 was accomplished by sequential coupling of specific dipeptides (RG and DV) (V = valine) and by coupling of the RGD-containing hexapeptide GRGDSP (S = serine, P = proline). Two types of gel were prepared by sequential coupling, designated as G10 (acetone) and G10 (dimethylformamide) (G10(DMF)), containing peptides which had been coupled to the outer side of the beads and throughout the porous beads, respectively. The binding capacity of the prepared Sephadex-derivatives amounted up to 2 x 10(9) human blood platelets per millilitre GRGDV-Sephadex at immobilized peptide concentrations, that were in the nanomole range (per millilitre packed gel) and which differed a factor 10 between G10 (acetone) and G10 (DMF). In a second series of experiments, different amounts of the hexapeptide GRGDSP were coupled to carboxylated Sephadex G-10 and carboxylated Sepharose CL 6B. The binding of human umbilical vein endothelial cells to the resulting materials was studied. Up to 10(6) endothelial cells attached per ml GRGDSP-derivatized hydrogel at peptide concentrations of 15 nmol GRGDSP/ml Sephadex and at +/- 300 nmol GRGDSP/ml Sepharose. Substitution of the arginine residue of the RGD-sequence by glutamine abolished the cell-binding activity of the immobilized peptide towards activated blood platelets but not towards endothelial cells. From the results of this study it can be concluded that small peptides can be coupled to the outer side of the porous Sephadex beads, resulting in high effective ligand densities for cell-affinity applications. In this respect, Sephadex G-10, derivatized according to 'the acetone method' is a good alternative for polystyrene and other solid phase materials.

Tresyl-activated support for high-performance affinity chromatography

A new activated support TSK gel Tresyl-5PW was evaluated for the coupling of antibodies, which was found to occur easily under mild conditions with high yields. Optimum coupling conditions were a 2-h reaction at 25 degrees C in 1 M phosphate buffer (pH 7.5) when 2-3 mg antibody/ml support is to be coupled and a 6-7-h reaction when ca. 10 mg antibody/ml support is to be coupled. When antibodies were coupled under these conditions, antibody coupling yields greater than 80% and antigen binding efficiencies of 70-80% were achieved, probably owing to a selective attachment of the Fc region of the antibodies. Antigens (human serum proteins) could be separated rapidly without denaturation on antibody-coupled Tresyl-5PW.

Immunoaffinity chromatography utilizing monoclonal antibodies. Factors which influence antigen-binding capacity

Differences in antigen-binding capacity of a monoclonal antibody coupled to Sepharose under varying conditions were explored. The extent of cyanogen bromide activation, and the pH of the coupling reaction had a profound effect upon the rate of antibody coupling, but only small differences in antigen-binding capacity were observed if the antibody coupling reaction was terminated when 80-90% of the antibody was covalently coupled to Sepharose. However, if antibody was incubated with activated resin until 100% coupling was attained, the antigen-binding capacity of the resulting immunoadsorbent decreased significantly. Monoclonal antibody coupled to Sepharose via an N-hydroxysuccinimide ester linkage and approximately half the antigen-binding capacity of antibody coupled by CNBr activation. Concentrations of monoclonal antibodies as high as 13 mg/ml of packed resin could be used without noticeable steric hindrance.

An experimental verification of the theory of diffusion limitation of immobilized enzymes

Alkaline phosphatase (orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) was covalently bound to Sepharose beads. Kinetic measurements with the substrate p-nitrophenyl phosphate gave the following results. Effectiveness factors were decreasing with increasing bound activity, decreasing substrate concentration, and increasing particle radius of the beads. With decreasing effectiveness factors, the apparent Michaelis constants were decreasing. Preparations with high bound activities did not obey Michaelis-Menten kinetics at substrate concentrations much higher than the apparent Michaelis constants. The experimental results accorded quantitatively with the theory of diffusion limitation (Engasser, J.M. (1978) Biochim. Biophys. Acta 526, 301-310).

Affinity chromatography of cells and cell membranes

This article attempts to introduce the concept of cellular affinity chromatography as it departs from molecular affinity chromatography. Special emphasis is placed on the selectio of a solid support as well as on the role of lectins as affinity ligands. Our major goal was to bring to light the basic principles involved, multiple options of ligands and matrices, and different techniques, which may be applied to separate the complex cell population as well as cell membranes. It is hoped that further developments in the field, especially in the selection of proper experimental conditions, ligands and matrix material may provide better results. We have tried to identify some of the potential problems which should be considered before these approaches can be used on a routine basis. Although the review deals primarily with the affinity chromatography of cells and cell membranes, examples are presented for diverse systems such as cell organelles, viruses and phages. A table summarizing the use of cellular affinity chromatography is included. It lists more than 80 examples covering the literature up to December, 1979.

Immobilized organelles and whole cells into protein foam structures: scanning and transmission electron microscope observations

Protein foam structures bearing cells and organelles were produced by using a co-crosslinking method with serum albumin and glutaraldehyde at sub-zero temperature. Morphological observations obtained with scanning and transmission electron microscopy indicate macroporous and homogeneous structures. The glutaraldehyde concentration was varied to reveal its effect on immobilized red cells. It was observed that the structural appearance of preatreated cells or subcellular fractions (thylakoids from lettuce ; spheroplasts and chromatophores from R. capsulata) is preserved during the immobilization process. The morphological features of foam particles are always related to the observed kinetic activities of the specimens.

Protein purification using immobilised triazine dyes

This review attempts to identify proteins which selectively interact with immobilised triazine dyes such as Cibacron blue F3GA and Procion red HE 3B. Different support matrices are compared by examining the capacities of these dyes for proteins. Various approaches to the immobilisation of triazine dyes are considered together with the use of spacers. Some theories of the mechanism of protein retardation by immobilised dyes are discussed. A number of methods are suggested for the measurement of dye concentrations and for the modification of the binding of proteins to dye columns. The variety of elution methods is compared with a view to optimizing purifications. The scope of applications is reviewed as well as the choice of dye. Some advantages of triazine dyes over other affinity ligands are given. It is concluded that although no satisfactory mechanism for the binding of triazine dyes to proteins has yet been proposed, these dyes possess considerable potential for protein purification, particularly when applied on the large scale.

Comparison of activation and blocking procedures in the use of defined antigen substrate spheres (DASS) for quantitative and visual assessment of conjugate activity

The use of Sepharose beads in the defined antigen substrate sphere (DASS) immunofluorescent system has been restricted by the need for sophisticated equipment for fluorescence quantitation since reliable subjective reading is not possible. This paper describes a method for visual assessment of results in this system. Antigen is coupled to sodium metaperiodate activated. Cross-linked Sepharose 4B beads and blocked with rhodamine-BSA prior to reduction. This procedure eliminates the use of the hazardous cyanogen bromide activation process and is potentially suitable for use in both direct systems for evaluation of specificity and potency of fluorescent conjugates and in indirect systems for serological screening of sera for specific antibody.

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.