Breath chemical markers of sexual arousal in humans

The chemical composition of exhaled breath was examined for volatile organic compound (VOC) indicators of sexual arousal in human beings. Participants (12-male, 12-female) were shown a randomized series of three emotion-inducing 10-min film clips interspersed with 3-min neutral film clips. The films caused different arousals: sports film (positive-nonsexual); horror film (negative-nonsexual); and erotic (sexual) that were monitored with physiological measurements including genital response and temperature. Simultaneously the breath was monitored for VOC and CO₂. While some breath compounds (methanol and acetone) changed uniformly irrespective of the film order, several compounds did show significant arousal associated changes. For both genders CO₂ and isoprene decreased in the sex clip. Some male individuals showed particularly strong increases of indole, phenol and cresol coincident with sexual arousal that decreased rapidly afterwards. These VOCs are degradation products of tyrosine and tryptophan, precursors for dopamine, noradrenalin, and serotonin, and therefore represent potential breath markers of sexual arousal.

Rapid production of l-DOPA by Vibrio natriegens, an emerging next-generation whole-cell catalysis chassis

3, 4‐Dihydroxyphenyl‐l‐alanine (l‐DOPA) is a compound of high medical value and is considered effective as a treatment for Parkinson’s disease. Currently, bioproduction of l‐DOPA is mainly carried out by whole‐cell catalysis mediated by recombinant Escherichia coli carrying heterogeneous tyrosine phenol lyase. Vibrio natriegens is increasingly attracting attention owing to its superiority, including extremely rapid growth and high soluble protein expression capacity. In this study, we attempt to develop an efficient whole‐cell catalyst for l‐DOPA production using V. natriegens as the chassis. The maximum soluble protein expression by V. natriegens was accomplished in 4 h at 37°C, which was equivalent to that achieved by E. coli in 16 h at 16°C. Furthermore, the maximum productivity reached over 10.0 g l⁻¹ h⁻¹ in the early stage of biocatalysis, nearly two‐fold higher than previously reported. Approximately 54.0 g l⁻¹l‐DOPA was obtained with a catechol conversion rate greater than 95%. In conclusion, V. natriegens displays advantages, including rapid protein expression and catalytic rate in the catalysis process for l‐DOPA production. These findings strongly suggest that V. natriegens has remarkable potential as a whole‐cell catalysis chassis for the production of valuable chemicals.

RidA Proteins Protect against Metabolic Damage by Reactive Intermediates

The Rid (YjgF/YER057c/UK114) protein superfamily was first defined by sequence homology with available protein sequences from bacteria, archaea, and eukaryotes (L. Parsons, N. Bonander, E. Eisenstein, M. Gilson, et al., Biochemistry 42:80-89, 2003, https://doi.org/10.1021/bi020541w). The archetypal subfamily, RidA (reactive intermediate deaminase A), is found in all domains of life, with the vast majority of free-living organisms carrying at least one RidA homolog. In over 2 decades, close to 100 reports have implicated Rid family members in cellular processes in prokaryotes, yeast, plants, and mammals. Functional roles have been proposed for Rid enzymes in amino acid biosynthesis, plant root development and nutrient acquisition, cellular respiration, and carcinogenesis. Despite the wealth of literature and over a dozen high-resolution structures of different RidA enzymes, their biochemical function remained elusive for decades. The function of the RidA protein was elucidated in a bacterial model system despite (i) a minimal phenotype of ridA mutants, (ii) the enzyme catalyzing a reaction believed to occur spontaneously, and (iii) confusing literature on the pleiotropic effects of RidA homologs in prokaryotes and eukaryotes. Subsequent work provided the physiological framework to support the RidA paradigm in Salmonella enterica by linking the phenotypes of mutants lacking ridA to the accumulation of the reactive metabolite 2-aminoacrylate (2AA), which damaged metabolic enzymes. Conservation of enamine/imine deaminase activity of RidA enzymes from all domains raises the likelihood that, despite the diverse phenotypes, the consequences when RidA is absent are due to accumulated 2AA (or a similar reactive enamine) and the diversity of metabolic phenotypes can be attributed to differences in metabolic network architecture. The discovery of the RidA paradigm in S. enterica laid a foundation for assessing the role of Rid enzymes in diverse organisms and contributed fundamental lessons on metabolic network evolution and diversity in microbes. This review describes the studies that defined the conserved function of RidA, the paradigm of enamine stress in S. enterica, and emerging studies that explore how this paradigm differs in other organisms. We focus primarily on the RidA subfamily, while remarking on our current understanding of the other Rid subfamilies. Finally, we describe the current status of the field and pose questions that will drive future studies on this widely conserved protein family to provide fundamental new metabolic information.

Pyridoxal 5'-Phosphate-Dependent Enzymes at the Crossroads of Host-Microbe Tryptophan Metabolism

The chemical processes taking place in humans intersects the myriad of metabolic pathways occurring in commensal microorganisms that colonize the body to generate a complex biochemical network that regulates multiple aspects of human life. The role of tryptophan (Trp) metabolism at the intersection between the host and microbes is increasingly being recognized, and multiple pathways of Trp utilization in either direction have been identified with the production of a wide range of bioactive products. It comes that a dysregulation of Trp metabolism in either the host or the microbes may unbalance the production of metabolites with potential pathological consequences. The ability to redirect the Trp flux to restore a homeostatic production of Trp metabolites may represent a valid therapeutic strategy for a variety of pathological conditions, but identifying metabolic checkpoints that could be exploited to manipulate the Trp metabolic network is still an unmet need. In this review, we put forward the hypothesis that pyridoxal 5′-phosphate (PLP)-dependent enzymes, which regulate multiple pathways of Trp metabolism in both the host and in microbes, might represent critical nodes and that modulating the levels of vitamin B6, from which PLP is derived, might represent a metabolic checkpoint to re-orienteer Trp flux for therapeutic purposes.

Integrating enzyme evolution and high-throughput screening for efficient biosynthesis of l-DOPA

l-DOPA is a key pharmaceutical agent for treating Parkinson’s, and market demand has exploded due to the aging population. There are several challenges associated with the chemical synthesis of l-DOPA, including complicated operation, harsh conditions, and serious pollution. A biocatalysis route for l-DOPA production is promising, especially via a route catalyzed by tyrosine phenol lyase (TPL). In this study, using TPL derived from Erwinia herbicola (Eh-TPL), a mutant Eh-TPL was obtained by integrating enzyme evolution and high-throughput screening methods. l-DOPA production using recombinant Escherichia coli BL21 (DE3) cells harbouring mutant Eh-TPL was enhanced by 36.5% in shake flasks, and the temperature range and alkali resistance of the Eh-TPL mutant were promoted. Sequence analysis revealed two mutated amino acids in the mutant (S20C and N161S), which reduced the length of a hydrogen bond and generated new hydrogen bonds. Using a fed-batch mode for whole-cell catalysis in a 5 L bioreactor, the titre of l-DOPA reached 69.1 g L−1 with high productivity of 11.52 g L−1 h−1, demonstrating the great potential of Eh-TPL variants for industrial production of l-DOPA.

The role of endogenous bromotyrosine in health and disease

Bromotyrosine is a stable by-product of eosinophil peroxidase activity, a result of eosinophil activation during an inflammatory immune response. The elevated presence of bromotyrosine in tissue, blood, and urine in medical conditions involving eosinophil activation has highlighted the potential role of bromotyrosine as a medical biomarker. This is highly beneficial in a paediatric setting as a urinary noninvasive biomarker. However, bromotyrosine and its derivatives may exert biological effects, such as protective effects in the brain and pathogenic effects in the thyroid. Understanding these pathways may yield therapeutic advancements in medicine. In this review, we summarize the existing evidence present in literature relating to bromotyrosine formation and metabolism, identify the biological actions of bromotyrosine and evaluate the feasibility of bromotyrosine as a medical biomarker.

Nano-sized TiO2 (nTiO2) induces metabolic perturbations in Physarum polycephalum macroplasmodium to counter oxidative stress under dark conditions

Nano-sized TiO₂ (nTiO₂) exerts an oxidative effect on cells upon exposure to solar or UV irradiation and ecotoxicity of the nTiO₂ is an urgent concern. Little information is available regarding the effect of TiO₂ on cells under dark conditions. Metabolomics is a unique approach to the discovery of biomarkers of nTiO₂ cytotoxicity, and leads to the identification of perturbed metabolic pathways and the mechanism underlying nTiO₂ toxicity. In the present study, gas chromatography mass spectrometry (GC/MS)-based metabolomics was performed to investigate the effect of nTiO₂ on sensitive cells (P. polycephalum macroplasmodium) under dark conditions. According to the multivariate pattern recognition analysis, at least 60 potential metabolic biomarkers related to sugar metabolism, amino acid metabolism, nucleotide metabolism, polyamine biosynthesis, and secondary metabolites pathways were significantly perturbed by nTiO₂. Notably, many metabolic biomarkers and pathways were related to anti-oxidant mechanisms in the living organism, suggesting that nTiO₂ may induce oxidative stress, even under dark conditions. This speculation was further validated by the biochemical levels of reactive oxygen species (ROS), 8-hydroxy-2-deoxyguanosine (8-OHdG), and total soluble phenols (TSP). We inferred that the oxidative stress might be related to nTiO₂-induced imbalance of cellular ROS. To the best of our knowledge, the present study is the first to investigate the nTiO₂-induced metabolic perturbations in slime mold, provide a new perspective of the mechanism underlying nTiO₂ toxicity under dark conditions, and show that metabolomics can be employed as a rapid, reliable and powerful tool to investigate the interaction among organisms, the environment, and nanomaterials.

Arsenic hyperaccumulation induces metabolic reprogramming in Pityrogramma calomelanos to reduce oxidative stress

Arsenic (As) pollution is a major environmental concern due to its worldwide distribution and high toxicity to organisms. The fern Pityrogramma calomelanos is one of the few plant species known to be able to hyperaccumulate As, although the mechanisms involved are largely unknown. This study aimed to investigate the metabolic adjustments involved in the As-tolerance of P. calomelanos. For this purpose, ferns with five to seven fronds were exposed to a series of As concentrations. Young fronds were used for biochemical analysis and metabolite profiling using gas chromatography-mass spectrometry. As treatment increased the total concentration of proteins and soluble phenols, enhanced peroxidase activities, and promoted disturbances in nitrogen and carbon metabolism. The reduction of the glucose pool was one of the striking responses to As. Remarkable changes in amino acids levels were observed in As-treated plants, including those related to biosynthesis of glutathione and phenols, osmoregulation and two photorespiratory intermediates. In addition, increases in polyamines levels and antioxidant enzyme activities were observed. In summary, this study indicates that P. calomelanos tolerates high concentration of As due to its capacity to upregulate biosynthesis of amino acids and antioxidants, without greatly disturbing central carbon metabolism. At extremely high As concentrations, however, this protective mechanism fails to block reactive oxygen species production, leading to lipid peroxidation and leaf necrosis.

A straightforward kinetic evidence for coexistence of "induced fit" and "selected fit" in the reaction mechanism of a mutant tryptophan indole lyase Y72F from Proteus vulgaris

The interaction of the mutant tryptophan indole-lyase (TIL) from Proteus vulgaris Y72F with the transition state analogue, oxindolyl-l-alanine (OIA), with the natural substrate, l-tryptophan, and with a substrate S-ethyl-l-cysteine was examined. In the case of wild-type enzyme these reactions are described by the same kinetic scheme where binding of holoenzyme with an amino acid, leading to reversible formation of an external aldimine, proceeds very fast, while following transformations, leading finally to reversible formation of a quinonoid intermediate proceed with measureable rates. Principally the same scheme ("induced fit") is realized in the case of mutant Y72F enzyme reaction with OIA. For the reaction of mutant enzyme with l-Trp at lower concentrations of the latter a principally different kinetic scheme is observed. This scheme suggests that binding of the substrate and formation of the quinonoid intermediate are at fast equilibrium, while preceding conformational changes of the holoenzyme proceed with measureable rates ("selected fit"). For the reaction with S-ethyl-l-cysteine the observed concentration dependence of kobs agrees with the realization of both kinetic schemes, the "selected fit" becoming predominant at lower concentrations of substrate, the "induced fit"- at higher ones. In the reaction with S-ethyl-l-cysteine the formation of the quinonoid intermediate proceeds slower than does catalytic α,β-elimination of ethylthiol from S-ethyl-l-cysteine, and consequently does not play a considerable role in the catalysis, which may be effected by a concerted E2 mechanism.

Crystallographic snapshots of tyrosine phenol-lyase show that substrate strain plays a role in C-C bond cleavage

The key step in the enzymatic reaction catalyzed by tyrosine phenol-lyase (TPL) is reversible cleavage of the Cβ-Cγ bond of L-tyrosine. Here, we present X-ray structures for two enzymatic states that form just before and after the cleavage of the carbon-carbon bond. As for most other pyridoxal 5'-phosphate-dependent enzymes, the first state, a quinonoid intermediate, is central for the catalysis. We captured this relatively unstable intermediate in the crystalline state by introducing substitutions Y71F or F448H in Citrobacter freundii TPL and briefly soaking crystals of the mutant enzymes with a substrate 3-fluoro-L-tyrosine followed by flash-cooling. The X-ray structures, determined at ~2.0 Å resolution, reveal two quinonoid geometries: "relaxed" in the open and "tense" in the closed state of the active site. The "tense" state is characterized by changes in enzyme contacts made with the substrate's phenolic moiety, which result in significantly strained conformation at Cβ and Cγ positions. We also captured, at 2.25 Å resolution, the X-ray structure for the state just after the substrate's Cβ-Cγ bond cleavage by preparing the ternary complex between TPL, alanine quinonoid and pyridine N-oxide, which mimics the α-aminoacrylate intermediate with bound phenol. In this state, the enzyme-ligand contacts remain almost exactly the same as in the "tense" quinonoid, indicating that the strain induced by the closure of the active site facilitates elimination of phenol. Taken together, structural observations demonstrate that the enzyme serves not only to stabilize the transition state but also to destabilize the ground state.