Co(III) Complexes with N2(SO)2-Type Equatorial Planar Ligands Similar to the Active Center of Nitrile Hydratase:  Role of the Sulfenate Group in the Enzymatic Reaction

Abstract The role of the conserved glutamic acid residue in anionic plant peroxidases with regard to substrate specificity and stability was examined. A Glu141Phe substitution was generated in tobacco anionic peroxidase (TOP) to mimic neutral plant peroxidases such as horseradish peroxidase C (HRP C). The newly constructed enzyme was compared to wild-type recombinant TOP and HRP C expressed in E. coli. The Glu141Phe substitution supports heme entrapment during the refolding procedure and increases the reactivation yield to 30% compared to 7% for wild-type TOP. The mutation reduces the activity towards ABTS, o-phenylenediamine, guaiacol and ferrocyanide to 50% of the wild-type activity. No changes are observed with respect to activity for the lignin precursor substrates, coumaric and ferulic acid. The Glu141Phe mutation destabilizes the enzyme upon storage and against radical inactivation, mimicking inactivation in the reaction course. Structural alignment shows that Glu141 in TOP is likely to be hydrogen-bonded to Gln149, similar to the Glu143-Lys151 bond in Arabidopsis A2 peroxidase. Supposedly, the Glu141-Gln149 bond provides TOP with two different modes of stabilization: (1) it prevents heme dissociation, i.e., it ‘guards’ heme inside the active center; and (2) it constitutes a shield to protect the active center from solvent-derived radicals.

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On the Role of Tyrosine as Catalytic Base in Nitrile Hydratase

European Journal of Inorganic Chemistry ◽

10.1002/ejic.200800250 ◽

2008 ◽

Vol 2008 (22) ◽

pp. 3452-3459 ◽

Cited By ~ 8

Author(s):

Kathrin H. Hopmann ◽

Fahmi Himo

Keyword(s):

Nitrile Hydratase

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HPr: a model protein

Biochemistry and Cell Biology ◽

10.1139/o95-026 ◽

1995 ◽

Vol 73 (5-6) ◽

pp. 219-222

Author(s):

J. W. Anderson

Keyword(s):

Structure Function ◽

Active Center ◽

Active Site ◽

Central Component ◽

Active Site Residue ◽

Phosphotransferase System ◽

Function Model ◽

Model Protein

Histidine-containing protein (HPr) is a central component of the bacterial phosphoenolpyruvate: sugar phosphotransferase system (PTS). This brief review covers recent structure–function studies on the active center of this protein: the role of the active center residues in phosphotransfer; the residues contributing to the phosphohydrolysis properties of HPr; and the contribution residues in HPr make to the pKaof the transiently phosphorylated active-site residue, His 15. As well, the potential for HPr to be used as a model protein for studying problems not directly associated with its function in the PTS is discussed.Key words: phosphoenolpyruvate: sugar phosphotransferase system, histidine-containing protein, active center, structure–function, model protein.

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Role of Trace Elements in Breast Cancer and Their Characterization Using X-Ray Fluorescence Techniques

10.5772/intechopen.95491 ◽

2020 ◽

Author(s):

Harpreet Singh Kainth ◽

Deeksha Khandelwal ◽

Ranjit Singh ◽

Gurjeet Singh ◽

Sanjiv Puri

Keyword(s):

Breast Cancer ◽

Trace Elements ◽

Enzymatic Reaction ◽

Total Reflection ◽

Preparation Methods ◽

X Ray ◽

Causative Agents ◽

Serious Disease ◽

Sample Preparation Methods

Breast cancer is the most common serious disease that occurs in the human body. Trace elements have an important function in biological and metabolism processes including activation or inhibition of enzymatic reaction, reactive oxygen species (ROS), competition between trace elements and metal proteins for binding positions and modifications in the permeability of cellular membranes which influence carcinogenic processes. A significant association between the abnormal concentration of trace elements and breast cancer has been found in many studies using XRF techniques like energy dispersive X-ray fluorescence (EDXRF), particle induced X-ray emission (PIXE), total reflection X-ray fluorescence (TXRF), wavelength dispersive X-ray fluorescence (WDXRF) and synchrotron induced X-ray fluorescence (SRIXE). This chapter considers trace elements like Fe, Cu, Zn, Cr, Cl, Ca, P, S, K, Na, Mg, Se, As and Sr. from the standpoint of their role as either inhibitory or causative agents of breast cancer. XRF techniques and sample preparation methods for analysis of biological samples are also reviewed.

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