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. 2015 Apr 10;16(4):8040-58.
doi: 10.3390/ijms16048040.

Heavy metal complexation of thiol-containing peptides from soy glycinin hydrolysates

Xiuzhen Ding  1 , Yufei Hua  2 , Yeming Chen  3 , Caimeng Zhang  4 , Xiangzhen Kong  5
Affiliations

Heavy metal complexation of thiol-containing peptides from soy glycinin hydrolysates

Xiuzhen Ding et al. Int J Mol Sci. .

Abstract

Many thiol-containing molecules show heavy metal complexation ability and are used as antidotes. In this study, the potential function associated with thiol-containing peptides (TCPs) from soy protein hydrolysates as natural detoxicants for heavy metals is reported. TCPs enriched by Thiopropyl-Sepharose 6B covalent chromatography had different molecular weight distributions as well as different numbers of proton dissociable groups, depending on the proteases and degree of hydrolysis. The major contribution of sulfhydryl groups was confirmed by the largest pH decrease between 8.0 and 8.5 of the pH titration curves. The complexation of TCPs with heavy metals was evaluated by stability constants (βn) of TCP-metal complexes whose stoichiometry was found to be 1:1 (ML) and 1:2 (ML2). TCPs from degree of hydrolysis of 25% hydrolysates gave high affinities towards Hg2+, Cd2+, and Pb2+ (giving similar or even bigger lgβ values than that of glutathione). A significantly positive correlation was found between the logarithm of stability constants for ML2 (lgβ2) and the sulfhydryl group content. Molecular weight distribution of TCPs affected the complexation with Pb2+ notably more than Hg2+ and Cd2+. These results suggest that soy TCPs have the potential to be used in the formulation of functional foods to counteract heavy metal accumulation in humans.

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Figures

Figure 1
Figure 1
SEC-HPLC profiles of soy glycinin hydrolysates (SGHs) with different degree of hydrolysates (DH) obtained by enzymatic hydrolysis with alcalase (a), papain (b) and pepsin (c). The SEC-HPLC profiles are divided into 5 fractions. Inserted tables give the percentage of every fraction. Fraction I corresponds to protein fragments with molecular weight (Mw) exceeding 10 kDa, fraction II to protein fragments with Mw between 3 and 10 kDa, fraction III to protein fragments with Mw between 1 and 3 kDa, fraction IV to protein fragments with Mw between 0.5 and 1 kDa and fraction V to material with Mw lower than 0.5 kDa. Sample codes consist of 3 letters encoding the enzyme and 2 digits encoding the DH.
Figure 2
Figure 2
Total sulfhydryl group content of SGHs (□, ○, Δ) and sulfhydryl group content of thiol-containing peptides (TCPs) (■, ●, ▲) with different DH. Total sulfhydryl group content of SGHs was determined after reduction of disulfide bonds.
Figure 3
Figure 3
SEC-HPLC profiles of TCPs with different DH obtained by enzymatic hydrolysis with alcalase (a), papain (b) and pepsin (c).
Figure 4
Figure 4
pH titration curves of TCPs and TCPs (■) in the presence of Hg2+ (●), Cd2+ (▲) or Pb2+ (◆) at 25 °C, I = 0.1 M KCl. The red solid line pointing right emphasizes the change of inflexions of TCPs after presence of heavy metals. The distance between the dotted lines gives the extent of the change.
Figure 5
Figure 5
Correlations between content of sulfhydryl group and stability constants. (a) Hg2+; (b) Cd2+; (c) Pb2+.
Figure 5
Figure 5
Correlations between content of sulfhydryl group and stability constants. (a) Hg2+; (b) Cd2+; (c) Pb2+.
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