Biomedical Engineering Reference
In-Depth Information
450
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MeIQ
4,8-DiMeIQx
Trp-p-2
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50
0
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pH
Source : Inbaraj et al. 2006b.
Figure 12. Effect of pH on binding of heterocyclic amines (HA) by γ-PGA. HA concentration: 500
mg/L; γ-PGA dose: 5 mg/mL.
5.1. Binding of Mutagenic Heterocyclic Amines at Gastrointestinal pH
Inbaraj et al. [28] investigated the adsorption characteristics of three mutagenic
heterocyclic amines (HA), namely, MeIQ, 4,8-DiMeIQx and Trp-p-2, by γ-PGA from B.
subtilis (H-form; MW 990 kDa) at gastrointestinal pH conditions. Heterocyclic amines were
monitored by a HPLC method developed by Chen and Yang [122], who employed a binary
solvent system of acetonitrile and 0.05 ammonium acetate solution (pH 3.6) with the
following gradient elution: 9% A at 0 min, 15% A at 8 min, 27% at 18 min, 55% A at 28 min
and 100% A at 30 min. A batch-mode equilibrium study at different solution pH (1-7)
showed appreciable binding of all HAs over the entire gastrointestinal pH range typically
being 2.5 (stomach), 7.5 (small intestine), 5.5 (cecum/ascending colon) and 6.8 (distal colon)
(Figure 12). Binding curves developed at pH 2.5 and 5.5 exhibited different isotherm shapes
belonging to S and L types, respectively (plots not shown), according to classification by
Giles et al. [81]. The S-type curve at pH 2.5 was characterized by an initial concave portion
signifying less or no adsorption, which may be attributed to clustering or agglomeration of
HA molecules caused by repulsive force between protonated primary amino group of HA and
secondary amino group of γ-PGA. In contrast, at high HA concentration, the interaction
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