Species-Specific, pH-Independent, Standard Redox Potential of Selenocysteine and Selenocysteamine.

Tamás Pálla,Arash Mirzahosseini,Béla Noszál

doi:10.3390/antiox9060465

Tamás Pálla, Arash Mirzahosseini + Show 1 more

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https://doi.org/10.3390/antiox9060465

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Abstract

Microscopic redox equilibrium constants and standard redox potential values were determined to quantify selenolate-diselenide equilibria of biological significance. The highly composite, codependent acid-base and redox equilibria of selenolates could so far be converted into pH-dependent, apparent parameters (equilibrium constants, redox potentials) only. In this work, the selenolate-diselenide redox equilibria of selenocysteamine and selenocysteine against dithiothreitol were analyzed by quantitative nuclear magnetic resonance (NMR) methods to characterize the interfering acid-base and redox equilibria. The directly obtained, pH-dependent, conditional redox equilibrium constants were then decomposed by our method into pH-independent, microscopic constants, which characterize the two-electron redox transitions of selenocysteamine and selenocysteine. The 12 different, species-specific parameter values show close correlation with the respective selenolate basicities, providing a tool to estimate otherwise inaccessible site-specific selenolate-diselenide redox potentials of related moieties in large peptides and proteins.

Highlights

The role of selenium, the biological trace element and the related selenium-containing proteins has been described in numerous antioxidant processes [1]
In this the highly acid-base and redox pathways of selenolate-diselenide of biologically relevant selenolate-diselenide couples are determined for the first time; these values systems were decomposed into species-specific, component equilibria
The standard redox characterize redox processes the protonation microspecies level. The elucidation of these potentials ofthe biologically relevantatselenolate-diselenide couples are determined for the first time; redox microequilibria reveals considerable betweenmicrospecies the various level

Summary

Introduction

The role of selenium, the biological trace element and the related selenium-containing proteins (selenoproteins) has been described in numerous antioxidant processes [1]. Selenocysteine, known as the twenty-first amino acid, is the only selenium-containing building block of proteins that contains selenium. The majority of selenoproteins are enzymes (such as glutathione peroxidase [2], iodothyronine deiodinase [3], thioredoxin reductase [4]), most of which are involved in redox reactions. Their selenocysteine residue is the essential unit for their catalytic activity. A new, specific way to quantify redox properties at the submolecular level has recently been introduced to characterize thiols of biological importance (cysteine, cystamine, homocysteine and glutathione [5,6]; ovothiol A and penicillamine [5,7]). A major conclusion of these studies is that there is a close correlation between the thiolate basicities and the thiolate-disulfide redox properties [5–9]

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