Spectroscopic studies of interactions involving horseradish peroxidase and Tb3+

Synthesis of Pyridinic-Rich N, S Co-doped Carbon Quantum Dots as Effective Enzyme Mimics

N and S co-doped carbon quantum dots (N, S-CQDs) with high N- and S-doping level were synthesized by microwave solid-phase pyrolysis within 50 s. Owing to the dominant pyridinic N injection into the conjugated framework, both high enzyme mimics catalytic activity and photoluminescence quantum yield are achieved simultaneously.

Roles of horseradish peroxidase in response to terbium stress

The pollution of the environment by rare earth elements (REEs) causes deleterious effects on plants. Peroxidase plays important roles in plant response to various environmental stresses. Here, to further understand the overall roles of peroxidase in response to REE stress, the effects of the REE terbium ion (Tb(3+)) on the peroxidase activity and H2O2 and lignin contents in the leaves and roots of horseradish during different growth stages were simultaneously investigated. The results showed that after 24 and 48 h of Tb(3+) treatment, the peroxidase activity in horseradish leaves decreased, while the H2O2 and lignin contents increased. After a long-term (8 and 16 days) treatment with Tb(3+), these effects were also observed in the roots. The analysis of the changes in peroxidase activity and H2O2 and lignin contents revealed that peroxidase plays important roles in not only reactive oxygen species scavenging but also cell wall lignification in horseradish under Tb(3+) stress. These roles were closely related to the dose of Tb(3+), duration of stress, and growth stages of horseradish.

Direct interaction between terbium ion and peroxidase in horseradish at different pH values

Rare earth elements (REEs) entering plant cells can directly interact with peroxidase in plants, which is the structural basis for the decrease in the activity of peroxidase. Different cellular compartments have different pH values. However, little information is available regarding the direct interaction between REEs and peroxidase in plants at different pH values. Here, we investigated the charge distribution on the surface of horseradish peroxidase (HRP) molecule as well as the interaction of terbium ion (Tb(3+), one type of REEs) and HRP at different pH values. Using the molecular dynamics simulation, we found that when the pH value was from 4.0 to 8.0, a large amount of negative charges were intensively distributed on the surface of HRP molecule, and thus, we speculated that Tb(3+) with positive charges might directly interact with HRP at pH 4.0-8.0. Subsequently, using ultraviolet-visible spectroscopy, we demonstrated that Tb(3+) could directly interact with HRP in the simulated physiological solution at pH 7.0 and did not interact with HRP in other solutions at pH 5.0, pH 6.0 and pH 8.0. In conclusion, we showed that the direct interaction between Tb(3+) and HRP molecule depended on the pH value of cellular compartments.

A spectroscopic study of uranyl-cytochrome b5/cytochrome c interactions

Uranium is harmful to human health due to its radiation damage and the ability of uranyl ion (UO2(2+)) to interact with various proteins and disturb their biological functions. Cytochrome b5 (cyt b5) is a highly negatively charged heme protein and plays a key role in mediating cytochrome c (cyt c) signaling in apoptosis by forming a dynamic cyt b5-cyt c complex. In previous molecular modeling study in combination with UV-Vis studies, we found that UO2(2+) is capable of binding to cyt b5 at surface residues, Glu37 and Glu43. In this study, we further investigated the structural consequences of cyt b5 and cyt c, as well as cyt b5-cyt c complex, upon uranyl binding, by fluorescence spectroscopic and circular dichroism techniques. Moreover, we proposed a uranyl binding site for cyt c at surface residues, Glu66 and Glu69, by performing a molecular modeling study. It was shown that uranyl binds to cyt b5 (KD=10 μM), cyt c (KD=87 μM), and cyt b5-cyt c complex (KD=30 μM) with a different affinity, which slightly alters the protein conformation and disturbs the interaction of cyt b5-cyt c complex. Additionally, we investigated the functional consequences of uranyl binding to the protein surface, which decreases the inherent peroxidase activity of cyt c. The information of uranyl-cyt b5/cyt c interactions gained in this study likely provides a clue for the mechanism of uranyl toxicity.

Toxic effect of heavy metal terbium ion on cell membrane in horseradish

In order to understand the toxic mechanism of terbium ion (Tb(III)) on plants, the subcellular distribution of Tb(III) in horseradish, the effect of Tb(III) on the composition of the fatty acids in the cell membrane, the peroxidation of membrane lipid, the morphological character of protoplast, the cellular ultrastructure in horseradish were investigated using transmission electron microscopic autoradiography, molecular dynamics simulation, gas chromatography, scanning electron microscopy and transmission electron microscopy. The results show that Tb(III) could not enter the horseradish cell in the presence of 5 mgL(-1) Tb(III) and it was distributed on the cell wall and plasma membrane. The behavior caused the decrease in the contents of unsaturated fatty acids and then the increase in the peroxidation of membrane lipid. Thereby the structure of horseradish cell was damaged. The effects of Tb(III) mentioned above were aggravated in horseradish treated with 60 mgL(-1) Tb(III) because Tb(III) could enter the horseradish cell. It was a possible cytotoxic mechanism of Tb(III) on horseradish.

Inhibition mechanism of lanthanum ion on the activity of horseradish peroxidase in vitro

In order to understand the inhibition mechanism of lanthanum ion (La(3+)) on the activity of horseradish peroxidase (HRP), the effects of La(3+) on the activity, electron transfer and conformation of HRP in vitro were investigated by using cyclic voltammetry (CV), atomic force microscopy (AFM), circular dichroism (CD), high performance liquid chromatography (HPLC), matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF/MS) and inductively coupled plasma mass spectrometry (ICP-MS). It was found that La(3+) can combine with the amide groups of the polypeptide chain in HRP molecule, forming the complex of La(3+) and HRP (La-HRP). The formation of the La-HRP complex causes the destruction of the native structure of HRP molecule, leading to the decrease in the non-planarity of the porphyrin ring in the heme group of HRP molecule, and then in the exposure extent of active center, Fe(III) of the porphyrin ring of HRP molecule. Thus, the direct electrochemical and catalytic activities of HRP are decreased. It is a possible inhibition mechanism of La(3+) on the activity of peroxidase.

Electrochemical detection of glyphosate herbicide using horseradish peroxidase immobilized on sulfonated polymer matrix

This paper describes the use of horseradish peroxidase (HRP) based biosensor for novel detection of glyphosate herbicide. The biosensor was prepared by electrochemically depositing poly(2,5-dimethoxyaniline) (PDMA) doped with poly(4-styrenesulfonic acid) (PSS) onto the surface of a gold electrode followed by electrostatic attachment of the enzyme HRP onto the PDMA-PSS composite film. Fourier transform infrared (FTIR) and UV-Vis spectrometry inferred that HRP was not denatured during its immobilization on PDMA-PSS composite film. The biosensing principle was based on the determination of the cathodic responses of the immobilized HRP to H(2)O(2), before and after incubation in glyphosate standard solutions. Glyphosate inhibited the activity of HRP causing a decrease in its response to H(2)O(2). The determination of glyphosate was achieved in the range of 0.25-14.0 microg L(-1) with a detection limit of 1.70 microg L(-1). The apparent Michaelis-Menten constant (calculated for the HRP/PDMA-PSS biosensor in the presence and absence of glyphosate was found to be 7.73 microM and 7.95 microM respectively.