Biomedical Engineering Reference
In-Depth Information
ASPARTATE
GLUTAMATE
COO
-
COO
-
α
α
NH
3
+
NH
3
+
C
H
C
H
CH
2
CH
2
COO
-
CH
2
COO
-
ARGININE
HISTIDINE
LYSINE
COO
-
COO
-
COO
-
α
α
α
NH
3
+
NH
3
+
C
H
C
H
NH
3
+
C
H
CH
2
CH
2
CH
2
H
H
CH
2
C
CH
2
C
N
+
N
CH
2
CH
2
C
H
H
CH
2
NH
NH
3
+
C
NH
2
+
H
2
N
Figure 6.10
Structures of amino acids having overall net charges at pH 7.0. In proteins, the charges associ-
ated with the
α
-amino and
α
-carboxyl groups in all but the terminal amino acids are not present, as these
groups are directly involved in the formation of peptide bonds
During the cation-exchange process, positively charged proteins bind to the negatively
charged ion-exchange matrix by displacing the counter ion (often H
), which is initially
bound to the resin by electrostatic attraction. Elution may be achieved using a salt-containing
irrigation buffer. The salt cation, often Na
of NaCl, in turn displaces the protein from the
ion-exchange matrix. In the case of negatively charged proteins, an anion exchanger is obvi-
ously employed, with the protein adsorbing to the column by replacing a negatively charged
counter ion.
The vast majority of purifi cation procedures employ at least one ion-exchange step; it repre-
sents the single most popular chromatographic technique in the context of protein purifi cation. Its
popularity is based upon the high level of resolution achievable, its straightforward scale-up (for
industrial application), together with its ease of use and ease of column regeneration. In addition,
Search WWH ::
Custom Search