APPLICATION OF A NATURAL BIOPOLYMER POLY (y-GLUTAMIC ACID) AS A BIOFLOCCULANT AND ADSORBENT FOR CATIONIC DYES AND CHEMICAL MUTAGENS: AN OVERVIEW/Title> - Biochemical Engineering - page 108

higher than that obtained by the Langmuir equation for saturation of all layers (Table 13),
implying the multimolecular HA adsorption did occur for at least two layers on γ-PGA.
According to the generalized polarization theory by DeBoer and Zwicker [125], the
adsorption of non-polar molecules on ionic adsorbents like γ-PGA may induce dipoles in the
first layer of adsorbed molecules, which in turn may stimulate dipoles on the second layer
favoring a multilayer adsorption. Based on the hydrophobic character of HAs and ionic nature
of γ-PGA, the adsorption on first layer may be formed by hydrogen-bonding, hydrophobic
and ionic interactions, while the subsequent layer(s) may result from weak dipole-dipole and
hydrophobic interactions.

Table 12. Langmuir and Scatchard plot parameters for heterocyclic amines binding by
γ -PGA at pH 5.5 a

HA Curve I Curve II

r 2 r 2 q m (mg/g) b (l/mg) q m (mg/g) b (l/mg)

Langmuir model parameters

MeIQ 500.00 0.2632 0.989 1428.57 0.0374 0.999

4,8-DiMeIQx 370.37 0.2030 0.991 1000.00 0.0152 0.999

Trp-p-2 500.00 0.6897 0.982 1666.67 0.0211 0.999

Scatchard plot parameters

MeIQ 499.16 0.1805 0.918 1465.09 0.0432 0.983

4,8-DiMeIQx 397.79 0.0706 0.994 944.68 0.0169 0.991

Trp-p-2 454.30 1.5903 0.913 1619.74 0.0228 0.995

Source : Inbaraj et al. 2006b.
a Experimental conditions: HA concentration range: 10-2000 mg/L; γ-PGA dose: 1 mg/mL.

Table 13. BET isotherm parameters for heterocyclic amines binding
by γ -PGA at pH 5.5 a

HA BET model parameters

r 2

q m (mg/g)

a

MeIQ 653.60 51.00 0.867

4,8-DiMeIQx 370.37 451.00 0.961

Trp-p-2 623.44 401.00 0.989

Source : Inbaraj et al. 2006b.
a Experimental conditions: HA concentration range: 10-2000 mg/L; γ-PGA dose: 1 mg/mL.

5.2. Suppressive Effect on SOS Response of Salmonella typhimurium Induced
by Chemical Mutagens

Sato et al. [32] recently reported the suppressive effect of γ-PGA (Na form) from B.
subtilis on SOS response (a post replication DNA repair system that allow DNA replication to
bypass lesions) of Salmonella typhimurium (TA1535/pSK1002) induced by direct and
indirect forms of chemical mutagens (AF-2, MNNG, 4NQO, Trp-p-2, IQ and MeIQx). The
antimutagenicity was determined by a slightly modified umu test [126], which was based on
the ability of γ-PGA to suppress the umu operon expression induced by DNA-damaging