Biomedical Engineering Reference
In-Depth Information
chemical mutagens. A plasmid (pSK 1002) carrying fusion gene
umu
C-
lac
Z was introduced
into
S. typhimurium
TA 1535 and the percentage of suppression was calculated in terms of the
β-galactosidase activity of cells resulting from the expression and suppression of the
umu
operon
according to the equation: (1-A/B) x 100, where A and B are the β-galactosidase
activity with and without γ-PGA, respectively. The concentration of chemical mutagens used
to induce the SOS response in
S. typhimurium
was 0.3, 6, 3, 0.3, 0.3 or 3 μg/mL of AF-2,
MNNG, 4NQO, IQ, MeIQx or Trp-p-2, respectively, which was chosen based on induction of
β-galactosidase activity without affecting the cell growth.
The γ-PGA (Na form; 4000 kDa) tested at three different concentrations (1, 2 and 3%)
showed a substantial suppressive effect on the SOS response induced by all the mutagens,
with >80% suppression being achieved by a 3% solution (Figure 13).
Irrespective of the type
of chemical mutagen, the antimutagenic activity tested for γ-PGA (3%) with different
molecular masses (50-8000 kDa) exhibited a lower effect at 50 kDa and >6000 kDa when
compared to others, with maximum activity being shown for γ-PGA at 4000 kDa (Figure 3).
The low water-holding capacity of γ-PGA at 50 kDa and the three dimensional structure or
the rheological property of γ-PGA at >6000 kDa may be responsible for the less-pronounced
effect in entrapping the mutagens [32]. However, the variation in salt form of γ-PGA (Na, K
or Ca) did not show any remarkable suppressive effect on the SOS response induced by
indirect mutagens (IQ, MeIQx and Trp-p-2), implying the difference in electronegativity or
valency of metal ions poses no significant impact. The antimutagenic activity of γ-PGA (3%
of 4000 kDa) was also compared with its monomer units, D- and L-glutamic acids (Na form),
and some other reference compounds like carboxymethylcellulose (CMC) and xanthan gum
(XG) [32]. The percentage of suppression by γ-PGA was the highest for all chemical
mutagens, followed by XG, CMC, and D- and L-glutamates (Table 14). Although XG and
CMC are similar to γ-PGA in possessing carboxyl groups, the difference in antimutagenic
activity was large, probably because of variation in ion exchange capacity (meq/g) between γ-
PGA (8.7) and XG (2.0) or CMC (0.68). Besides, the γ-PGA also exhibited significant
antimutagenic effect on the SOS response of
S. typhimurium
induced by the active forms
(nitrenium ions) of three indirect mutagens (Trp-p-2, IQ and MeIQx) [32].
Table 14. Suppressive effect of
γ
-PGA
a
and reference compounds on SOS response of S.
typhimurium induced by various chemical mutagens
Mutagen
(Final concentration)
Suppression (%)
CMC
b
XG
c
LG
d
DG
e
γ
-PGA
25
40
15
12
90
AF-2 (0.3 μg/mL)
MNNG (6 μg/mL)
30
72
20
18
80
40
75
20
22
81
4NQO (3 μg/mL)
20
48
38
43
90
IQ (0.3 μg/mL)
35
70
17
25
90
MeIQx (0.3 μg/mL)
30
43
27
25
82
Trp-p-2 (3 μg/mL)
Source
: Sato et al. 2008.
a
3% Na-form γ-PGA at 4000 kDa;
b
carboxymethylcellulose;
c
xanthan gum;
d
L-glutamic acid;
e
D-glutamic acid.
