Separation of serum proteins on a Fe3+-monohydroxamate adsorbent

Adsorption and selectivity characteristics of several human serum proteins with immobilised hard Lewis metal ion-chelate adsorbents

In this investigation, human serum has been used as an example of a crude protein mixture to define the protein binding characteristics and selectivity of several immobilised hard Lewis metal ion affinity chromatographic (IMAC) adsorbents. Specifically, the binding properties of immobilised O-phosphoserine (im-OPS) and 8-hydroxyquinoline (im-8-HQ), with immobilised iminodiacetic acid as a control system, have been investigated in combination with the hard Lewis metal ions, Al3+, Ca2+, Fe3+, Yb3+, and the borderline metal ion, Cu2+, over the pH range pH 5.5 to pH 8.0 with buffers of 0.5 M ionic strength. The same IMAC adsorbents were also investigated for their protein binding capabilities with buffers of an ionic strength of 0.06 M at pH 5.5 and pH 8.0. The binding behaviour of four "marker" proteins, namely transferrin, alpha2-macroglobulin, gammaglobulin and human serum albumin have furthermore been employed to monitor the differences in protein selectivity exhibited by these IMAC systems. The experimental findings confirm that these hard Lewis metal ion IMAC adsorbents function in a "mixed" binding mode with both coordination and electrostatic characteristics evident, depending on the ionic strength and pH of the equilibration or elution buffers. Based on a screening protocol, several members of the im-Mn+-8-HQ and im-Mn+-OPS adsorbent series have been identified with high selectivity for transferrin and alpha2-macroglobulin. These hard Lewis metal ion IMAC adsorbents thus provide attractive alternatives for selective fractionation of human serum proteins.

New ligand, N-(2-pyridylmethyl)aminoacetate, for use in the immobilised metal ion affinity chromatographic separation of proteins

A new chelating compound has been developed for use in the immobilised metal ion affinity chromatographic separation of proteins. The tridentate ligand, sodium N-(2-pyridylmethyl)aminoacetate (carbpyr), 1, was prepared via a one-step synthesis from 2-picolylamine, 3 and then immobilised onto Sepharose CL-4B through the epoxide coupling procedure. The binding behaviour of the resulting IMAC sorbent, following chelation with Cu2+ ions to a density of 152 micromol Cu2+ ions/g gel was characterised by frontal analysis experiments using horse heart myoglobin (HMYO) at pH 7.0 and pH 9.0. From the derived isotherms, the adsorption capacity, q(m), for the binding of HMYO to immobilised Cu2+-N-(2-pyridylmethyl)aminoacetate (im-Cu2+-carbpyr)-Sepharose CL-4B at these pH values was found to be 1.92 and 1.91 micromol/g sorbent, respectively, whilst the dissociation constants K(D) were 0.0092 x 10(-6) M and 0.0062 x 10(-6) M at pH 7.0 and pH 9.0, respectively, indicating that the HMYO-im-Cu2+-N-(2-pyridylmethyl)aminoacetate complex was more stable under alkaline conditions, although the binding capacity in terms of micromol protein/g gel remained essentially unchanged. The selectivity features of the im-Cu2+-carbpyr-Sepharose CL-4B sorbent were further characterised in terms of the binding properties with several human serum proteins at pH 5.0, pH 7.0 and pH 9.0.

Protein selectivity with immobilized metal ion-tacn sorbents: chromatographic studies with human serum proteins and several other globular proteins

The chromatographic selectivity of the immobilized chelate system, 1,4,7-triazocyclononane (tacn), complexed with the borderline metal ions Cu2+, Cr3+, Mn2+, Co2+, Zn2+, and Ni2+ has been investigated with hen egg white lysozyme, horse heart cytochrome c, and horse skeletal muscle myoglobin, as well as proteins present in partially fractionated preparations of human plasma. The effects of ionic strength and pH of the loading and elution buffers on protein selectivities of these new immobilized metal ion affinity chromatographic (IMAC) systems have been examined. The results confirm that immobilized Mn;pl-tacn sorbents exhibit a novel type of IMAC behavior with proteins. In particular, the chromatographic properties of these immobilized M(n+)-tacn ligand systems were significantly different compared to the IMAC behavior observed with other types of immobilized tri- and tetradentate chelating ligands, such as iminodiacetic acid, O-phosphoserine, or nitrilotriacetic acid, when complexed with borderline metal ions. The experimental results have consequently been evaluated in terms of the additional contributions to the interactive processes mediated by effects other than solely the conventional lone pair Lewis soft acid-Lewis soft base coordination interactions, typically found for the IMAC of proteins with borderline and soft metal ions, such as Cu2+ or Ni2+.

Protein selectivity in immobilized metal affinity chromatography based on the surface accessibility of aspartic and glutamic acid residues

The interaction of different species variants of cytochrome c and myoglobin, as well as hen egg white lysozyme, with the hard Lewis metal ions Al3+, Ca2+, Fe3+, and Yb3+ and the borderline metal ion Cu2+, immobilized to iminodiacetic acid (IDA)-Sepharose CL-4B, has been investigated over the range pH 5.5-8.0. With appropriately chosen buffer and metal ion conditions, these proteins can be bound to the immobilized Mn+-IDA adsorbents via negatively charged amino acid residues accessible on the protein surface. For example, tuna heart cytochrome c, which lacks surface-accessible histidine residues, readily bound to the Fe3+-IDA adsorbent, while the other proteins also showed affinity toward immobilized Fe3+-IDA adsorbents when buffers containing 30 mM of imidazole were used. These studies document that protein selectivity can be achieved with hard-metal-ion immobilized metal ion affinity chromatography (IMAC) systems through the interaction of surface-exposed aspartic and glutamic acid residues on the protein with the immobilized Mn+-IDA complex. These investigations have also documented that the so-called soft or borderline immobilized metal ions such as the Cu2+-IDA adsorbent can also interact with surface-accessible aspartic and glutamic acid residues in a protein-dependent manner. A relationship is evident between the number of clustering of the surface-accessible aspartic and glutamic residues and protein selectivity with these IMAC systems. The use of elution buffers which contain organic compound modifiers which replicate the carboxyl group moieties of these amino acids on the surface of proteins is also described.

Purification and determination of the binding site of lactate dehydrogenase from chicken breast muscle on immobilized ferric ions

Lactate dehydrogenase from chicken breast muscle was purified to homogeneity in one step by immobilized metal ion affinity chromatography. The purified enzyme was used to localize the binding site to immobilized Fe(III) ions. After cyanogen bromide degradation and digestion with trypsin, small enzyme fragments capable of binding to immobilized Fe(III) ions were obtained. It is proposed that several histidyl groups are involved in the binding.

Preparation of ferric adsorbent paper and its interaction with phosphate-containing biomolecules

A procedure for the synthesis of a selective adsorbent for phosphate-containing biomolecules is described. The sorbent is based on Whatman chromatography paper, which is activated with epichlorohydrine, followed by the coupling of iminodiacetic acid to the active surface of the sorbent. The immobilized complex-forming chelating groups are saturated with ferric ions. The synthesized adsorbent is a counterpart to Chelating Sepharose and makes it possible to extend the use of immobilized ferric chelating groups for analytical purposes. It displays a high affinity towards compounds containing free terminal phosphate groups (phosphopeptides, nucleotides). The results of the binding experiments are compared to the corresponding data obtained with Chelating Sepharose gels.