Types of Affinity Ligands Used

A number of affinity ligands have been used and some are presented in Table 2. The attachment of ligand to polymers and the purification of the ligand-polymer differs from case to case. Some ligands such as reactive texile dyes can be bound directly to PEG and to dextran in water solution of high pH. Other ligands are introduced by reactions in organic solvent, such as the attachment of acyl groups to PEG by reaction with acyl chloride in toluene. PEG may also be transformed into a more reactive form such as bromo-PEG, tosyl-PEG or tresyl-PEG. Some reaction pathways are shown in Figure 7. A number

Table 2 Examples of affinity partitioning

Figure 6 The effect of adenosine triphosphase (ATP) and of ATP + Mg2+ on the partitioning of phosphofructokinase from bakers' yeast in a system containing Cibacron blue F3G-A PEG (Cb-PEG). A log K of enzyme as function of concentration of ATP. Without addition of Mg2 + (O); and with 10 mM MgCl2 (•). System composition: 7%w/w dextran 500 and 5% w/w PEG 8000 including 0.5% Cb-PEG (of total PEG). 50 mM sodium phosphate buffer pH 7.0, 0.5 mM EDTA, 5 mM 2-mercaptoethanol, and 4 nkat g_1 enzyme. Temperature, 00C.

Table 2 Examples of affinity partitioning

Partitioned substance

Ligand

Colipase

Lecithin

Dehydrogenases and kinase

Textile dyes

a-Fetoprotein

Remazol yellow

Haemoglobin and phosphovitin

Cu(II)-chelate

Liver plasma membranes

Lectin

Myeloma protein

Dinitrophenol

Nucleic acids

Dyes

Oxosteroid isomerase

Oestradiol

Red blood cells

Antibodies

Serum albumins, histones and

Fatty acids

lactalbumin

Synaptic membranes

Opiates and antagonists

Trypsin

p-Aminobenzamidine

Figure 7 Some reactions used for the covalent linkage of ligands to polymers, preferentially to PEG. The encircled 'L' represents the ligand and the open circles the polymer chain.

of methods to synthesize polymer derivatives have been published by Harris.

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