Enhancement of nitrite on heme-induced oxidative reactions: A potential toxicological implication

Understanding the Role of the Antioxidant System and the Tetrapyrrole Cycle in Iron Deficiency Chlorosis

Iron deficiency chlorosis (IDC) is an abiotic stress often experienced by soybean, owing to the low solubility of iron in alkaline soils. Here, soybean lines with contrasting Fe efficiencies were analyzed to test the hypothesis that the Fe efficiency trait is linked to antioxidative stress signaling via proper management of tissue Fe accumulation and transport, which in turn influences the regulation of heme and non heme containing enzymes involved in Fe uptake and ROS scavenging. Inefficient plants displayed higher oxidative stress and lower ferric reductase activity, whereas root and leaf catalase activity were nine-fold and three-fold higher, respectively. Efficient plants do not activate their antioxidant system because there is no formation of ROS under iron deficiency; while inefficient plants are not able to deal with ROS produced under iron deficiency because ascorbate peroxidase and superoxide dismutase are not activated because of the lack of iron as a cofactor, and of heme as a constituent of those enzymes. Superoxide dismutase and peroxidase isoenzymatic regulation may play a determinant role: 10 superoxide dismutase isoenzymes were observed in both cultivars, but iron superoxide dismutase activity was only detected in efficient plants; 15 peroxidase isoenzymes were observed in the roots and trifoliate leaves of efficient and inefficient cultivars and peroxidase activity levels were only increased in roots of efficient plants.

Effect of protein structure and/or conformation on the dityrosine cross-linking induced by haem-hydrogen peroxide

BACKGROUND

Haem, an essential cofactor in aerobic organisms, can cause oxidative stress and impose toxic effects on tissues and organs. It can induce aggregation of proteins via dityrosine cross-linking and cause neurodegenerative diseases. Although dityrosine cross-linking in many proteins induced by haem has been reported, not all the proteins have the same effect or the efficiency of cross-linking varies, while the reason has not been clarified.

METHODS

The correlation of protein structure/conformation with its aggregation tendency via dityrosine induced by hematin (oxidized form of haem) in the presence of hydrogen peroxide (H2O2) was studied through reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), fluorescence and circular dichroism (CD) measurements, and the mechanism was investigated by performing UV-Vis absorbance, Raman spectroscopy and low-temperature electron spin resonance (ESR) experiments.

RESULTS

It was found that proteins in unstructured state are more readily to be cross-linked via dityrosine formation by hematin-H2O2. The unstructured protein without steric effect can coordinate with hematin to form six-coordinated protein-hematin complex, in which the produced tyrosyl radicals by H2O2 are with high tendency to dimerize to form dityrosine.

CONCLUSIONS

Our results demonstrate that protein structure/conformation can affect its coordination state with haem, and the tendency of reaction of two tyrosyl radicals, further influencing the yield and efficiency of dityrosine cross-linking in the presence of H2O2.

GENERAL SIGNIFICANCE

This research can help to deepen our understanding of the protein aggregation and inactivation mechanisms in varied sophisticated conditions, and especially give us the new insight into the toxic effects under haem stress.

Membrane lipids and nuclear DNA are differently susceptive to Fenton reaction substrates in porcine thyroid

Fenton reaction (Fe(2+)+H(2)O(2) → Fe(3+)+()OH+OH(-)) is of special significance in the thyroid, as both substrates are indispensable for thyroid hormone synthesis, therefore being available presumably at high concentrations under physiological conditions. The study aimed at evaluation if both Fenton reaction substrates are required to induce oxidative damage to membrane lipids and nuclear DNA in porcine thyroid homogenates, and if these macromolecules are vulnerable to the same extent. Thyroid homogenates and nuclear DNA were incubated in the presence of H(2)O(2) and/or Fe(2+). Malondialdehyde+4-hydroxyalkenals (MDA+4-HDA) concentration (lipid peroxidation index) was measured spectrophotometrically, and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) concentration (DNA damage index) by HPLC. Whereas Fenton reaction substrates, used separately, did not affect lipid peroxidation, they increased 8-oxodG level for the highest H(2)O(2) concentration (100mM) and in Fe(2+) concentration-dependent manner (300, 150, 30 and 15 μM). If Fe(2+) and H(2)O(2) were applied together, lipid peroxidation increased significantly, however without H(2)O(2) concentration- but with clear Fe(2+) concentration-dependent effect. Concerning DNA damage, Fe(2+) enhanced H(2)O(2) effect, whereas Fe(2+) concentration-dependent effect was not changed by H(2)O(2). Excess of exclusively one of Fenton reaction substrates is sufficient to induce oxidative DNA damage, but not lipid peroxidation, in porcine thyroid. Comparing to H(2)O(2), Fe(2+) seems to be a stronger damaging substrate.