Avidin Column Research Articles

Liquid Phase Enzyme Reactor, a New Bioreactor Principle

One of the drawbacks of solid phase enzyme reactors is the sharp decrease in substrate affinity as shown by an increase in the Km app value. To circumvent this problem a liquid phase enzyme reactor system was designed. Biotin labeled L-Tryptophan side chain oxidase (TSO) was directly injected into the plasma circuit of a filter plasmaphoresis system of rabbits and adsorbed onto an Avidin column prior to its reentry into the animal's general blood circulation. In five experiments total L-Tryptophan depletion could be observed in the plasma circuit during 60 minutes of the experiment with complete readsorption of the enzyme to the Avidin column.

Characterization of ATP11 and detection of the encoded protein in mitochondria of Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, expression of functional F1-ATPase requires two proteins encoded by the ATP11 and ATP12 genes. Mutations in either gene block some crucial late step in assembly of F1, causing the alpha and beta subunits to accumulate in mitochondria as inactive aggregates (Ackerman, S. H., and Tzagoloff, A. (1991) Proc. Natl. Acad. Sci. U.S.A. 87, 4986-4990). In the present study we have cloned and determined the sequence of ATP11. The encoded product is protein of 37 kDa with no obvious homology to any known protein. In vitro import assays of ATP11 precursor and immunochemical evidence indicate that the protein is located in mitochondria. A fusion was made between ATP11 and a short sequence coding for 78 amino acids with the biotination signal of bacterial transcarboxylase. The protein expressed from this construct complements atp11 mutants, indicating that the addition of the extra 78 amino acids at the carboxyl terminus of the ATP11 protein does not compromise its function. The hybrid protein is detected in mitochondria with antibodies and with peroxidase-conjugated avidin. Biotinated ATP11 protein can be partially purified by affinity chromatography on monomeric or tetrameric avidin coupled to Sepharose. A fraction eluted from the avidin column and enriched for the biotinated ATP11 protein also contains the alpha and beta subunits of F1-ATPase.

Avidin column as a highly efficient and stable alternative for immobilization of ligands for affinity chromatography

The avidin/biotin system was applied as a general mediator in the adsorption/desorption or immobilization of biologically active macromolecules to solid supports. In this context, model biotinylated proteins (lectins and antibodies) were attached to avidin-coupled Sepharose. As examples for affinity chromatography, peanut agglutinin and anti-transferrin antibody were used to isolate asialofetuin and transferrin, respectively. The capacity and product yields were significantly better than those achieved with conventional affinity chromatography on CNBr-activated Sepharose columns containing the same lectin or antibody. Moreover, the columns were characterized by improved stability properties exhibiting remarkably low levels of leakage.

Solubilization and purification of rat pituitary gonadotropin-releasing hormone receptor.

Gonadotropin-releasing hormone (GnRH) receptors were solubilized from rat pituitary membrane preparations in an active form by using the zwitterionic detergent CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid). The solubilized receptor exhibits high affinity, saturability, and specificity. The soluble supernatant retained 100% of the original binding activity when stored at 4 or -20 degrees C in the presence of 10% glycerol. The receptors were resolved into two components on the basis of chromatography on wheat germ agglutinin-agarose. Homogeneous receptor preparation was obtained by two cycles of affinity chromatography on immobilized avidin column coupled to [biotinyl-D-Lys6]GnRH. The overall recovery of the purified receptor was 4-10% of the initial activity in the CHAPS extract, and the calculated purification -fold was approximately 10,000 to 15,000. Analysis of iodinated purified GnRH receptors by autoradiography indicated the presence of two bands, Mr = 59,000 and 57,000. This was confirmed by photoaffinity labeling of the partially purified receptors and suggests that both components can specifically bind the hormone.

Affinity chromatography of DNA labeled with chemically cleavable biotinylated nucleotide analogs

DNA labeled with the chemically cleavable biotinylated nucleotide Bio-12-SS-dUTP was chromatographed on biotin cellulose affinity columns using either avidin or streptavidin as the affinity reagent. Although both proteins were equally effective in binding the Bio-12-SS-DNA to the affinity resin, two important differences were found. First, nonbiotinylated DNA bound to avidin, but not to streptavidin, in buffers containing 50 m m NaCl. Second, Bio-12-SS-DNA was released much more slowly from the streptavidin affinity column than from the avidin column upon washing with buffer containing dithiothreitol. This difficulty in reducing the disulfide bond of Bio-12-SS-DNA bound to streptavidin is most likely due to steric protection of the disulfide bond by the protein. This conclusion is supported by our finding that DNA labeled with another biotinylated nucleotide analog, Bio-19-SS-dUTP, is rapidly and efficiently recovered from a streptavidin column. In Bio-19-SS-DNA, the distance between the disulfide bond and the biotin group is approximately 10 Å greater than that in Bio-12-SS-DNA. Therefore, Bio-19-SS-dUTP and streptavidin form the basis of an efficient affinity system for the isolation and subsequent recovery of biotinylated DNA in the presence of low ionic strength buffers.

3-( N-maleimido-propionyl) biocytin: A versatile thiol-specific biotinylating reagent

A biotin-containing, thiol-specific reagent, 3-( N-maleimido-propionyl) biocytin (MPB), was synthesized and used to biotinylate various proteins via native or artificially induced sulfhydryl groups. In combination with appropriate avidin- or streptavidin-conjugated markers (i.e., fluorescent, enzyme-conjugated, electron-dense, etc.), MPB essentially constitutes a universal, multipurpose, thiol-specific probe. The reagent could be used to detect protein SH groups on dot blots with sensitivities in the femtomole range. The labeling was very specific for sulfhydryl groups or reduced SS bonds; proteins lacking free SH groups were unlabeled by this method. Due to the long spacer between the biotinyl group and the reactive maleimide, improved adsorption of biotinylated proteins to avidin columns was achieved. An SH-containing enzyme (β-galactosidase) was biotinylated with MPB, and the resultant biotinylated enzyme could be used as an efficient histochemical probe. The use of this reagent is recommended to biotinylate proteins which contain nonessential SH groups or which can be easily thiolylated prior to reaction with MPB.

Investigations of the structure of 3-methylcrotonyl-CoA carboxylase from Achromobacter.

It was shown by gel electrophoresis in sodium dodecylsulphate solution that 3-methylcrotonyl-CoA carboxylase from Achromobacter IVS is composed of two different subunits with molecular weights of about 78000 and 96000, respectively. The biotin is bound to the heavier subunit. It was previously found that 3-methylcrotonyl-CoA carboxylase contains four biotin molecules per complex. A complex composed of four of each subunit would thus have a molecular weight of about 700000. This is compatible with the molecular weight of 760000 determined earlier by analytical ultracentrifugation. Both subunits were isolated preparatively. As the subunits, unlike the complex, are very sensitive to oxygen, special precautions had to be taken during isolation. The biotin-containing subunit was isolated by chromatography on DEAE-cellulose in 5 M urea. It no longer catalyzed the overall reaction, yet could still carboxylate free biotin. The biotin-free subunit was separated after dissociation of the enzyme by three-days' dialysis at pH 9.8 under nitrogen. On chromatography over a Sepharose-bound avidin column, the biotin-subunit was fixed and the biotin-free subunit was eluted unretarded. The latter subunit showed no enzymic activity. After the addition of the biotin-containing subunit, overall activity was regenerated. The speed of reassociation is very much enhanced by 3-methylcrotonyl-CoA. It was shown by reassociation experiments under different conditions that probably an initial complex, AxBy is formed, possessing a binding site for 3-methylcrotonyl-CoA. Upon the binding of this substrate the conformation may be changed to a form favourable for reconstitution. Finally, the structures of biotin enzymes from different sources are compared. In the course of evolution there is a tendency toward integration of the different constituent proteins into only one polypeptide chain.