Downstream processing - Pharmaceutical Biotechnology: Concepts and Aapplications - page 155

Procion Blue MX 3G

X O NH 2

SO 3 -

Cl

N

One X = SO 3 -
Other X = H

NH

X O NH N

N

SO 3 -

Cl

Procion Red H-3B

Cl

N

SO 3 -

OH NH N

N

N N

NH

- O 3 S

SO 3 -

Procion Yellow H-A

Cl

SO 3 -

N

N

N N NH

N

NH 2

NHCOCH 3

SO 3 -

Figure 6.16 Some mono- and di-chloro triazine dyes commonly used as affi nity ligands in dye affi nity
chromatography

6.6.9 Metal chelate affi nity chromatography

Metal chelate affi nity chromatography is a pseudoaffi nity protein purifi cation technique fi rst de-
veloped in the 1970s. The mode of adsorption relies upon the formation of weak coordinate bonds
between basic groups on a protein surface with metal ions immobilized on chromatographic beads
( Figure 6.17). The affi nity medium is synthesized by covalent attachment of a metal chelator to the
chromatographic bead via a spacer arm. Chelating agents, such as iminodiacetate, are capable of
binding a number of metal ions (e.g. Fe, Co, Ni, Cu, Zn, Al), and binding effectively immobilizes
the ion on the bead. The affi nity gel is normally supplied without bound metal, so the gel can
be 'charged' with the metal of choice (by fl ushing the column with a solution containing a salt
of that metal, e.g. CuSO 4 in the case of copper). The metal ions most commonly used are Zn 2 ,
Ni 2 and Cu 2 . Basic groups on protein surfaces, most notably the side chain of histidine residues,