A theoretical approach to the link between oxidoreductions and pyrite formation in the early stage of evolution

The evolutionary arch of bioenergetics from prebiotic mechanisms to the emergence of a cellular respiratory chain

This article proposes an evolutionary trajectory for the development of biological energy producing systems. Six main stages of energy producing system evolution are described, from early evolutionary pyrite-pulled mechanism through the Last Universal Common Ancestor (LUCA) to contemporary systems. We define the Last Pure Chemical Entity (LPCE) as the last completely non-enzymatic entity. LPCE could have had some life-like properties, but lacked genetic information carriers, thus showed greater instability and environmental dependence than LUCA. A double bubble model is proposed for compartmentalization and cellularization as a prerequisite to both highly efficient protein synthesis and transmembrane ion-gradient. The article finds that although LUCA predominantly functioned anaerobically, it was a non-exclusive anaerobe, and sulfur dominated metabolism preceded phosphate dominated one.

Metabolic Shades of S-D-Lactoylglutathione

S-D-lactoylglutathione (SDL) is an intermediate of the glutathione-dependent metabolism of methylglyoxal (MGO) by glyoxalases. MGO is an electrophilic compound that is inevitably produced in conjunction with glucose breakdown and is essentially metabolized via the glyoxalase route. In the last decades, MGO metabolism and its cytotoxic effects have been under active investigation, while almost nothing is known about SDL. This article seeks to fill the gap by presenting an overview of the chemistry, biochemistry, physiological role and clinical importance of SDL. The effects of intracellular SDL are investigated in three main directions: as a substrate for post-translational protein modifications, as a reservoir for mitochondrial reduced glutathione and as an energy currency. In essence, all three approaches point to one direction, namely, a metabolism-related regulatory role, enhancing the cellular defense against insults. It is also suggested that an increased plasma concentration of SDL or its metabolites may possibly serve as marker molecules in hemolytic states, particularly when the cause of hemolysis is a disturbance of the pay-off phase of the glycolytic chain. Finally, SDL could also represent a useful marker in such metabolic disorders as diabetes mellitus or ketotic states, in which its formation is expected to be enhanced. Despite the lack of clear-cut evidence underlying the clinical and experimental findings, the investigation of SDL metabolism is a promising field of research.

Evolutionary Aspects of the Oxido-Reductive Network of Methylglyoxal

In the chemoautotrophic theory for the origin of life, offered as an alternative to broth theory, the archaic reductive citric acid cycle operating without enzymes is in the center. The non-enzymatic (methyl)glyoxalase pathway has been suggested to be the anaplerotic route for the reductive citric acid cycle. In the recent years, much has been learned about methylglyoxal, but its importance in the metabolic machinery is still uncovered. If methylglyoxal had been essential participant of the early stage of evolution, then it is a legitimate question whether it might have played a role in the early oxido-reduction network, too. Therefore, an oxido-reduction network of methylglyoxal that might have functioned under ancient circumstances without enzymes was constructed and analyzed by virtue of group contribution method. Taking methylglyoxal as input material, it turned out that the evolutionary value of reactions and biomolecules were not similar. Glycerol, glycerate, and tartonate, the output components, were conserved to different degrees. Although the tartonate route was similarly favorable from energetic point of view, its intermediates are almost not present in extant biochemistry. The presence of two carboxyl or aldehyde groups, or their combination in tricarbons of the constructed network seemed disadvantageous for selection, and the inductive effect, resulting in an asymmetry in electron cloud of chemicals, might have been important. The evolutionary role for cysteine, H₂S, and formaldehyde in the emergence of high-energy bonds in the form of thioesters and in Fe-S cluster formation as well as in imidazole synthesis was shown to bridge the gap between prebiotic chemistry and contemporary biochemistry. Overall, the ideas developed here represent an approach fitting to chemoautotrophic origin of life and implying to the role of methylglyoxal in triose formation. The proposed network is expected to have an impact upon how one may think of prebiological chemical processes on methylglyoxal, too. Finally, along the evolutionary time line, the network functioning without enzymes is situated between the formation of simple organic compounds and primeval cells, being closer to the former and well preceding the last common metabolic ancestor developed after primitive cells emerged.

The Reactive Species Interactome: Evolutionary Emergence, Biological Significance, and Opportunities for Redox Metabolomics and Personalized Medicine

SIGNIFICANCE

Oxidative stress is thought to account for aberrant redox homeostasis and contribute to aging and disease. However, more often than not, administration of antioxidants is ineffective, suggesting that our current understanding of the underlying regulatory processes is incomplete. Recent Advances: Similar to reactive oxygen species and reactive nitrogen species, reactive sulfur species are now emerging as important signaling molecules, targeting regulatory cysteine redox switches in proteins, affecting gene regulation, ion transport, intermediary metabolism, and mitochondrial function. To rationalize the complexity of chemical interactions of reactive species with themselves and their targets and help define their role in systemic metabolic control, we here introduce a novel integrative concept defined as the reactive species interactome (RSI). The RSI is a primeval multilevel redox regulatory system whose architecture, together with the physicochemical characteristics of its constituents, allows efficient sensing and rapid adaptation to environmental changes and various other stressors to enhance fitness and resilience at the local and whole-organism level.

CRITICAL ISSUES

To better characterize the RSI-related processes that determine fluxes through specific pathways and enable integration, it is necessary to disentangle the chemical biology and activity of reactive species (including precursors and reaction products), their targets, communication systems, and effects on cellular, organ, and whole-organism bioenergetics using system-level/network analyses.

FUTURE DIRECTIONS

Understanding the mechanisms through which the RSI operates will enable a better appreciation of the possibilities to modulate the entire biological system; moreover, unveiling molecular signatures that characterize specific environmental challenges or other forms of stress will provide new prevention/intervention opportunities for personalized medicine. Antioxid. Redox Signal. 00, 000-000.

FeS/S/FeS(2) redox system and its oxidoreductase-like chemistry in the iron-sulfur world

The iron-sulfur world (ISW) theory is an intriguing prediction regarding the origin of life on early Earth. It hypothesizes that life arose as a geochemical process from inorganic starting materials on the surface of sulfide minerals in the vicinity of deep-sea hot springs. During the last two decades, many experimental studies have been carried out on this topic, and some interesting results have been achieved. Among them, however, the processes of carbon/nitrogen fixation and biomolecular assembly on the mineral surface have received an inordinate amount of attention. To the present, an abiotic model for the oxidation-reduction of intermediates participating in metabolic pathways has been ignored. We examined the oxidation-reduction effect of a prebiotic FeS/S/FeS(2) redox system on the interconversion between several pairs of α-hydroxy acids and α-keto acids (i.e., lactate/pyruvate, malate/oxaloacetate, and glycolate/glyoxylate). We found that, in the absence of FeS, elemental sulfur (S) oxidized α-hydroxy acids to form corresponding keto acids only at a temperature higher than its melting point (113°C); in the presence of FeS, such reactions occurred more efficiently through a coupled reaction mechanism, even at a temperature below the phase transition point of S. On the other hand, FeS was shown to have the capacity to reversibly reduce the keto acids. Such an oxidoreductase-like chemistry of the FeS/S/FeS(2) redox system suggests that it can determine the redox homeostasis of metabolic intermediates in the early evolutionary phase of life. The results provide a possible pathway for the development of primordial redox biochemistry in the iron-sulfur world. Key Words: Iron-sulfur world-FeS/S/FeS(2) redox system-Oxidoreductase-like chemistry. Astrobiology 11, 471-476.

Prebiotic metabolism: production by mineral photoelectrochemistry of alpha-ketocarboxylic acids in the reductive tricarboxylic acid cycle

A reductive tricarboxylic acid (rTCA) cycle could have fixed carbon dioxide as biochemically useful energy-storage molecules on early Earth. Nonenzymatic chemical pathways for some steps of the rTCA cycle, however, such as the production of the alpha-ketocarboxylic acids pyruvate and alpha-ketoglutarate, remain a challenging problem for the viability of the proposed prebiotic cycle. As a class of compounds, alpha-ketocarboxylic acids have high free energies of formation that disfavor their production. We report herein the production of pyruvate from lactate and of alpha-ketoglutarate from pyruvate in the millimolar concentration range as promoted by ZnS mineral photoelectrochemistry. Pyruvate is produced from the photooxidation of lactate with 70% yield and a quantum efficiency of 0.009 at 15 degrees C across the wavelength range of 200-400 nm. The produced pyruvate undergoes photoreductive back reaction to lactate at a 30% yield and with a quantum efficiency of 0.0024. Pyruvate alternatively continues in photooxidative forward reaction to alpha-ketoglutarate with a 50% yield and a quantum efficiency of 0.0036. The remaining 20% of the carbon follows side reactions that produce isocitrate, glutarate, and succinate. Small amounts of acetate are also produced. The results of this study suggest that alpha-ketocarboxylic acids produced by mineral photoelectrochemistry could have participated in a viable enzyme-free cycle for carbon fixation in an environment where light, sulfide minerals, carbon dioxide, and other organic compounds interacted on prebiotic Earth.

Methylglyoxal and glucose metabolism: a historical perspective and future avenues for research

Methylglyoxal, an alpha-oxoaldehyde discovered in the 1880s, has had a hectic scientific career, at times being considered of fundamental importance and at other times viewed as playing a very subordinate role. Much has been learned about methylglyoxal, but the function of its production in the metabolic machinery is still unknown. This paper gives an overview of the changing role of methylglyoxal from a historical aspect and arrives at the conclusion that methylglyoxal is tightly bound to glycolysis from an evolutionary perspective, its production therefore being inevitable. It is not situated in the main stream of the glycolytic sequence, but a role can be assigned to its production in the phosphate supply of operating glycolysis in some prokaryotes and yeast under conditions of phosphate deficiency. This function is presumed to be performed by the enzyme methylglyoxal synthase, which is specialized for the conversion of dihydroxyacetone-phosphate to methylglyoxal. However, it is still unknown whether this enzyme and this kind of regulation also exist in animals.

The energetics of the reductive citric acid cycle in the pyrite-pulled surface metabolism in the early stage of evolution

The chemoautotrophic theory concerning the origin of life postulates that a central role is played in the prebiotic chemical machinery by a reductive citric acid cycle operating without enzymes. The crucial point in this scenario is the formation of pyrite from hydrogen sulfide and ferrous sulfide, a reaction suggested to be linked to endergonic reactions, making them exergonic. This mechanism is believed to provide the driving force for the cycle to operate as a carbon dioxide fixation network. The present paper criticizes the thermodynamic calculations and their presentation in the original version of the archaic reductive citric acid cycle [Wächtershäuser, 1990. Evolution of the first metabolic cycles. Proc. Natl Acad. Sci. USA 87, 200-204.]. The most significant differences between the Wächtershäuser hypothesis and the present proposal: Wächtershäuser did not consider individual reactions in his calculations. A particularly questionable feature is the involvement of seven molecules of pyrite which does not emerge as a direct consequence of the chemical reactions presented in the archaic reductive citric acid cycle. The involvement of a considerable number of sulfur-containing organic intermediates as building blocks is also disputed. In the new scheme of the cycle proposed here, less free energy is liberated than hypothesized by Wächtershäuser, but it has the advantages that the free energy changes for the individual reactions can be calculated, the number of pyrite molecules involved in the cycle is reduced, and fewer sulfur-containing intermediates are required for the cycle to operate. In combination with a plausible route for the anaplerotic reactions [Kalapos, 1997a. Possible evolutionary role of methylglyoxalase pathway: anaplerotic route for reductive citric acid cycle of surface metabolists. J. Theor. Biol. 188, 201-206.], this new presentation of the cycle assigns a special meaning to hydrogen sulfide formation in the early stage of biochemical evolution.