Lysine Oxidation Research Articles

Selective determination of lysine in mozzarella cheese using a novel potentiometric biosensor

ABSTRACT The analysis of lysine represents a significant cost for the relevant food industries. The use of an enzymatic sensor would allow the reduction of time and cost of this analysis. An enzymatic sensor using lysine -α- oxidase (LOx) with a soluble enzyme sensor in combination with an oxygen electrode was optimized in this study to determine the lysine content in mozzarella cheese. Selective determination of lysine in mozzarella cheese is an indicator of quality and of ripening time. The potentiometric signal obtained due to oxygen depletion (consumed oxygen) during lysine oxidation was carried out during 100s in the soluble enzyme sensor. An optimal time sensor response to quantify the lysine content of 3.5s was calculated from the slope of reaction rates. The sensor was set at a potential of 0.6 mV. A positive linear relationship was found between consumed oxygen as a function of time (mg O2/L × s) and lysine concentration in the range of 30–1,300 µM, with a coefficient of R2 = 0.9968 for the soluble enzyme sensor. This system showed good specificity (KM = 0.03 mM), which continued during eight weeks of cheese ripening time. The analysis of lysine with the soluble enzyme sensor in mozzarella cheese samples revealed very good agreement with the determination performed through standard HPLC methodology, which validated the use of this sensor as an alternative and more efficient technique to evaluate dairy products.

Deglutarylation of glutaryl-CoA dehydrogenase by deacylating enzyme SIRT5 promotes lysine oxidation in mice

A wide range of protein acyl modifications has been identified on enzymes across various metabolic processes; however, the impact of these modifications remains poorly understood. Protein glutarylation is a recently identified modification that can be nonenzymatically driven by glutaryl-CoA. In mammalian systems, this unique metabolite is only produced in the lysine and tryptophan oxidative pathways. To better understand the biology of protein glutarylation, we studied the relationship between enzymes within the lysine/tryptophan catabolic pathways, protein glutarylation, and regulation by the deglutarylating enzyme sirtuin 5 (SIRT5). Here, we identify glutarylation on the lysine oxidation pathway enzyme glutaryl-CoA dehydrogenase (GCDH) and show increased GCDH glutarylation when glutaryl-CoA production is stimulated by lysine catabolism. Our data reveal that glutarylation of GCDH impacts its function, ultimately decreasing lysine oxidation. We also demonstrate the ability of SIRT5 to deglutarylate GCDH, restoring its enzymatic activity. Finally, metabolomic and bioinformatic analyses indicate an expanded role for SIRT5 in regulating amino acid metabolism. Together, these data support a feedback loop model within the lysine/tryptophan oxidation pathway in which glutaryl-CoA is produced, in turn inhibiting GCDH function via glutaryl modification of GCDH lysine residues and can be relieved by SIRT5 deacylation activity.

Pyridoxine-Dependent Epilepsy and Antiquitin Deficiency Resulting in Neonatal-Onset Refractory Seizures.

Pyridoxine-dependent epilepsy (PDE) is an autosomal recessive neurometabolic disorder due to a deficiency of α-aminoadipic semialdehyde dehydrogenase (mutation in ALDH7A1 gene), more commonly known as antiquitin (ATQ). ATQ is one of the enzymes involved in lysine oxidation; thus, its deficiency leads to the accumulation of toxic metabolites in body fluids. PDE is characterized by persistent, recurrent neonatal seizures that cannot be well controlled by antiepileptic drugs but are responsive clinically and electrographically to daily pyridoxine (vitamin B6) supplementation. Although the phenotypic spectrum distinguishes between typical and atypical, pyridoxine-dependent is true for each. Diagnosis may pose a challenge mainly due to the rarity of the disorder and the fact that seizures may not occur until childhood or even late adolescence. Moreover, patients may not demonstrate an obvious clinical or electroencephalography response to the initial dose of pyridoxine. Effective treatment requires lifelong pharmacologic supplements of pyridoxine, and dietary lysine restriction and arginine enrichment should improve prognosis and avoid developmental delay and intellectual disability. The purpose of this review is to summarize briefly the latest reports on the etiology, clinical symptoms, diagnosis, and management of patients suffering from pyridoxine-dependent epilepsy.

An in vitro assay of the effect of lysine oxidation end-product, α-aminoadipic acid, on the redox status and gene expression in probiotic Lactobacillus reuteri PL503

This study was designed to gain information about the underlying mechanisms of the effects of a food-occurring free oxidized amino acid, α-aminoadipic acid (AAA), on the probiotic Lactobacillus reuteri PL503. This bacterium was incubated in colonic-simulated conditions (37 °C for 24 h in microaerophilic conditions) and exposed to three food-compatible AAA concentrations, namely, 1 mM, 5 mM, and 10 mM. A control group with no AAA exposure was also considered. Each of the four experimental conditions was replicated three times and samplings were collected at 12, 16, 20, and 24 h. The downregulation of the uspA gene by AAA (0.5-fold decrease as compared to control) suggests that AAA is identified as a potential chemical threat. The dhaT gene, implicated in the antioxidant defense, was found to be upregulated in bacteria treated with 1 and 5 mM AAA (up to twofold increase, as compared to control), which suggest the ability of the oxidized amino acid to impair the redox status of the bacterium. In fact, AAA caused an increased production of reactive oxygen species (ROS) and the accretion of post-translational changes (protein carbonylation) in L. reuteri (up to 13 nmol allysine/mg protein vs 1.8 nmol allysine/mg protein in control). These results suggest that probiotic bacteria identify oxidized amino acids as harmful species and activate mechanisms that may protect themselves and the host against their noxious effects.

Enzymatic lysine oxidation as a posttranslational modification.

Oxidoreductases catalyze oxidation-reduction reactions and comprise a very large and diverse group of enzymes, which can be subclassified depending on the catalytic mechanisms of the enzymes. One of the most prominent oxidative modifications in proteins is carbonylation, which involves the formation of aldehyde and keto groups in the side chain of lysines. This modification can alter the local macromolecular structure of proteins, thereby regulating their function, stability, and/or localization, as well as the nature of any protein-protein and/or protein-nucleic acid interactions. In this review, we focus on copper-dependent amine oxidases, which catalyze oxidative deamination of amines to aldehydes. In particular, we discuss oxidation reactions that involve lysine residues and that are regulated by members of the lysyl oxidase (LOX) family of proteins. We summarize what is known about the newly identified substrates and how this posttranslational modification regulates protein function in different contexts.

Oxidative deamination of lysine residues by polyphenols generates an equilibrium of aldehyde and 2-piperidinol products

Polyphenols, especially catechol-type polyphenols, exhibit lysyl oxidase–like activity and mediate oxidative deamination of lysine residues in proteins. Previous studies have shown that polyphenol-mediated oxidative deamination of lysine residues can be associated with altered electrical properties of proteins and increased crossreactivity with natural immunoglobulin M antibodies. This interaction suggested that oxidized proteins could act as innate antigens and elicit an innate immune response. However, the structural basis for oxidatively deaminated lysine residues remains unclear. In the present study, to establish the chemistry of lysine oxidation, we characterized oxidation products obtained via incubation of the lysine analog N-biotinyl-5-aminopentylamine with eggshell membranes containing lysyl oxidase and identified a unique six-membered ring 2-piperidinol derivative equilibrated with a ring-open product (aldehyde) as the major product. By monitoring these aldehyde–2-piperidinol products, we evaluated the lysyl oxidase–like activity of polyphenols. We also observed that this reaction was mediated by some polyphenols, especially o-diphenolic-type polyphenols, in the presence of copper ions. Interestingly, the natural immunoglobulin M monoclonal antibody recognized these aldehyde–2-piperidinol products as an innate epitope. These findings establish the existence of a dynamic equilibrium of oxidized lysine and provide important insights into the chemopreventive function of dietary polyphenols for chronic diseases.

Postruminal protein supply upregulates hepatic lysine oxidation and ornithine transcarbamoylase in lactating dairy cattle

Metabolizable protein supply is a limiting factor for milk production in dairy cows, and the availability of AA is a function of the quantity of the metabolizable protein available and of hepatic AA catabolism. This study aimed to evaluate the effect of postruminal protein infusion on key genes for ureagenesis and AA catabolism. Six multiparous Holstein cows in early lactation were used in a replicated crossover design. Cows were fed a TMR and infused postruminally with either 0 or 600 g/d of milk protein isolate. Periods were 21 d long, consisting of 14 d of adjustment to surroundings, followed by 7 d of protein infusion. On the last day of each infusion, liver samples were collected for mRNA analysis and explant culture, milk samples were collected for mRNA analysis, and blood samples were collected for plasma metabolite analysis. Postruminal infusion of protein increased milk yield by 10.5%, milk fat yield by 12.5%, milk protein yield by 20%, milk lactose yield by 11%, and total solids yield by 15.5%. Postruminal infusion of protein increased milk urea N by 23.5%, blood urea N by 18.6%, and the abundance of hepatic ornithine transcarbamoylase mRNA by 52.8%. Postruminal infusion of protein did not alter the mRNA abundance of hepatic argininosuccinate synthase, α-aminoadipate semialdehyde synthase, cysteine sulfinic acid decarboxylase, or cystathionase. The abundance of RNA for milk proteins was unchanged with postruminal protein infusion. Metabolism of l-[U 14C] Lys to CO2 was increased by 127% (0.143 vs. 0.063 ± 0.04 nmol product·mg tissue-1·h-1), and the metabolism of l-[U 14C] Ala to CO2 increased by 40.5% (0.52 vs. 0.37 ± 0.06 nmol product·mg tissue-1·h-1) with postruminal protein infusion. The rate of l-[1-14C] Met oxidation did not differ. These data indicate increased ureagenesis matched by upregulation of nonessential AA catabolism and a disproportional increase in Lys oxidation in response to increased postruminal protein infusion.

Consensus guidelines for the diagnosis and management of pyridoxine-dependent epilepsy due to α-aminoadipic semialdehyde dehydrogenase deficiency.

Pyridoxine-dependent epilepsy (PDE-ALDH7A1) is an autosomal recessive condition due to a deficiency of α-aminoadipic semialdehyde dehydrogenase, which is a key enzyme in lysine oxidation. PDE-ALDH7A1 is a developmental and epileptic encephalopathy that was historically and empirically treated with pharmacologic doses of pyridoxine. Despite adequate seizure control, most patients with PDE-ALDH7A1 were reported to have developmental delay and intellectual disability. To improve outcome, a lysine-restricted diet and competitive inhibition of lysine transport through the use of pharmacologic doses of arginine have been recommended as an adjunct therapy. These lysine-reduction therapies have resulted in improved biochemical parameters and cognitive development in many but not all patients. The goal of these consensus guidelines is to re-evaluate and update the two previously published recommendations for diagnosis, treatment, and follow-up of patients with PDE-ALDH7A1. Members of the International PDE Consortium initiated evidence and consensus-based process to review previous recommendations, new research findings, and relevant clinical aspects of PDE-ALDH7A1. The guideline development group included pediatric neurologists, biochemical geneticists, clinical geneticists, laboratory scientists, and metabolic dieticians representing 29 institutions from 16 countries. Consensus guidelines for the diagnosis and management of patients with PDE-ALDH7A1 are provided.

Impact of enteral arginine supplementation on lysine metabolism in humans: A proof-of-concept for lysine-related inborn errors of metabolism.

Patients with lysine-related inborn errors of metabolism (pyridoxine-dependent epilepsy [PDE] and glutaric aciduria type 1 [GA1]), follow a lysine-restricted diet with arginine-fortified lysine-free amino acid formula and additional oral arginine supplementation as a newer therapy for PDE. The rationale of arginine supplementation is based on arginine's ability to compete with lysine transport across cell membranes via shared transporter systems. Adequate doses of arginine required to competitively inhibit enteral lysine uptake has not been studied in humans This proof-of-concept study investigates the effect of incremental enteral arginine doses on whole-body lysine oxidation using an in vivo stable isotope tracer, L-[1-13 C] lysine, in healthy humans. Five healthy men completed six study days each consuming one dose of l-arginine HCl per study day; range = 50-600 mg/kg/d. Lysine intake was at DRI (30 mg/kg/d). Breath samples were analysed for L-[1-13 C] lysine oxidation to 13 CO2 using an isotope ratio mass spectrometer. Plasma amino acid concentrations were analysed using an amino acid analyser. Increasing doses of l-arginine HCl caused a linear decrease in whole-body lysine oxidation. Plasma arginine concentration increased, and plasma lysine concentration decreased below normal range with high arginine intakes. We provide the first empirical evidence of arginine-lysine antagonism in response to increasing oral arginine doses. Results suggest 300-600 mg/kg/d of l-arginine HCl and lysine intake restricted to DRI is needed to reduce enteral lysine uptake and systemic lysine oxidation. This could potentially lead to a recommended dose for arginine in lysine-related inborn errors of metabolism.

Asporin-deficient mice have tougher skin and altered skin glycosaminoglycan content and structure

The main structural component of connective tissues is fibrillar, cross-linked collagen whose fibrillogenesis can be modulated by Small Leucine-Rich Proteins/Proteoglycans (SLRPs). Not all SLRPs’ effects on collagen and extracellular matrix in vivo have been elucidated; one of the less investigated SLRPs is asporin. Here we describe the successful generation of an Aspn-/- mouse model and the investigation of the Aspn-/- skin phenotype. Functionally, Aspn-/- mice had an increased skin mechanical toughness, although there were no structural changes present on histology or immunohistochemistry. Electron microscopy analyses showed 7% thinner collagen fibrils in Aspn-/- mice (not statistically significant). Several matrix genes were upregulated, including collagens (Col1a1, Col1a2, Col3a1), matrix metalloproteinases (Mmp2, Mmp3) and lysyl oxidases (Lox, Loxl2), while lysyl hydroxylase (Plod2) was downregulated. Intriguingly no differences were observed in collagen protein content or in collagen cross-linking-related lysine oxidation or hydroxylation. The glycosaminoglycan content and structure in Aspn-/- skin was profoundly altered: chondroitin/dermatan sulfate was more than doubled and had an altered composition, while heparan sulfate was halved and had a decreased sulfation. Also, decorin and biglycan were doubled in Aspn-/- skin. Overall, asporin deficiency changes skin glycosaminoglycan composition, and decorin and biglycan content, which may explain the changes in skin mechanical properties.

Effect of moderate alterations of dietary protein or lysine on indices of lysine metabolism in liver, kidney and heart of growing pigs

Lysine addition to swine diets via either feed-grade lysine or protein sources costs producers. To better understand how diet affects lysine oxidation (LOX), weanling pigs were fed a control (C), high protein (HP), low protein (LP), high lysine (HL), or low lysine (LL) diets. No diet-induced alterations in lysine catabolism were detected in heart or kidney (P > 0.05). Liver lysine α-ketoglutarate reductase (LKR) (P < 0.05), saccharopine dehydrogenase (P < 0.05) activities, and α-aminoadipate δ-semialdehyde synthase abundance (P < 0.01) were reduced by 30%, 35%, and 52%, respectively, in pigs consuming LL compared with pigs consuming C. Expression of ornithine carrier-1 (ORC-1) mRNA in pigs fed HL was 170% greater (P < 0.05) than that in pigs fed C, whereas expression of the ORC-1 mRNA in pigs fed LL was 50% lower (P < 0.05) than that in pigs fed C. Expression of ORC-2 mRNA in pigs fed HL was 88% higher (P < 0.05) than that in pigs fed LL. The ORC transporters and LKR phosphorylation are likely points of r...

Myeloperoxidase-mediated protein lysine oxidation generates 2-aminoadipic acid and lysine nitrile in vivo

Recent studies reveal 2-aminoadipic acid (2-AAA) is both elevated in subjects at risk for diabetes and mechanistically linked to glucose homeostasis. Prior studies also suggest enrichment of protein-bound 2-AAA as an oxidative post-translational modification of lysyl residues in tissues associated with degenerative diseases of aging. While in vitro studies suggest redox active transition metals or myeloperoxidase (MPO) generated hypochlorous acid (HOCl) may produce protein-bound 2-AAA, the mechanism(s) responsible for generation of 2-AAA during inflammatory diseases are unknown. In initial studies we observed that traditional acid- or base-catalyzed protein hydrolysis methods previously employed to measure tissue 2-AAA can artificially generate protein-bound 2-AAA from an alternative potential lysine oxidative product, lysine nitrile (LysCN). Using a validated protease-based digestion method coupled with stable isotope dilution LC/MS/MS, we now report protein bound 2-AAA and LysCN are both formed by hypochlorous acid (HOCl) and the MPO/H2O2/Cl− system of leukocytes. At low molar ratio of oxidant to target protein Nε-lysine moiety, 2-AAA is formed via an initial Nε-monochloramine intermediate, which ultimately produces the more stable 2-AAA end-product via sequential generation of transient imine and semialdehyde intermediates. At higher oxidant to target protein Nε-lysine amine ratios, protein-bound LysCN is formed via initial generation of a lysine Nε-dichloramine intermediate. In studies employing MPO knockout mice and an acute inflammation model, we show that both free and protein-bound 2-AAA, and in lower yield, protein-bound LysCN, are formed by MPO in vivo during inflammation. Finally, both 2-AAA and to lesser extent LysCN are shown to be enriched in human aortic atherosclerotic plaque, a tissue known to harbor multiple MPO-catalyzed protein oxidation products. Collectively, these results show that MPO-mediated oxidation of protein lysyl residues serves as a mechanism for producing 2-AAA and LysCN in vivo. These studies further support involvement of MPO-catalyzed oxidative processes in both the development of atherosclerosis and diabetes risk.

Lysyl Oxidase Enhances the Deposition of Tropoelastin through the Catalysis of Tropoelastin Molecules on the Cell Surface.

The cross-linking of elastin by lysyl oxidase (LOX) family members is essential for the integrity and elasticity of elastic fibers, which play an important role in the characteristic resilience of various tissues. However, the temporal sequence of oxidation by LOX during elastic fiber formation is still incompletely understood. Here, we demonstrate that the cross-linking of tropoelastin molecules by LOX occurs concurrent with elastin deposition. Our data show that LOX deficiency or the inhibition of LOX enzyme activity leads to the loss of elastin deposition in skin fibroblast. Moreover, overexpression of LOX promotes the deposition and alignment of tropoelastin, whereas the addition of recombinant active-form of LOX in culture medium caused abnormal elastic fiber assembly. Immunoblotting and immunofluorescence show that LOX and tropoelastin are present together with fibronectin on the cell surface of preconfluent cultures. Further, fluorescence activated cell sorting (FACS) analysis for the localization of LOX on the cell surface reveals that the transfer of LOX to the extracellular space occurs in association with elastic fiber formation. In conclusion, our results support the view that LOX and tropoelastin are present on the cell surface and suggests the possibility that lysine oxidation by LOX precedes tropoelastin deposition onto microfibrils.

Mouse lysine catabolism to aminoadipate occurs primarily through the saccharopine pathway; implications for pyridoxine dependent epilepsy (PDE)

Lysine is catabolized in mammals through the saccharopine and pipecolate pathways — the former is mainly hepatic and renal, and the latter is believed to play a role in the cerebral lysine oxidation. Both pathways lead to the formation of aminoadipic semialdehyde (AASA) that is then oxidized to aminoadipate (AAA) by antiquitin (ALDH7A1). Mutations in the ALDH7A1 gene result in the accumulation of AASA and its cyclic form, piperideine-6-carboxylate (P6C), which causes pyridoxine-dependent epilepsy (PDE). P6C reacts with pyridoxal 5′-phosphate (PLP) causing its inactivation. Here, we used liquid chromatography–mass spectrometry to investigate lysine catabolism in mice injected with lysine labelled at either its nitrogen epsilon (ε-15N) or nitrogen alpha (α-15N). Analysis of ε-15N and α-15N lysine catabolites in plasma, liver and brain suggested the saccharopine as the main pathway for AAA biosynthesis. Although there was evidence for upstream cerebral pipecolate pathway activity, the resulting pipecolate does not appear to be further oxidized into AASA/P6C/AAA. By far the bulk of lysine degradation and therefore, the primary source of lysine catabolites are hepatic and renal. The results indicate that the saccharopine pathway is primarily responsible for body's production of AASA/P6C. The centrality of the saccharopine pathway in whole body lysine catabolism opens new possibilities of therapeutic targets for PDE. We suggest that inhibition of this pathway upstream of AASA/P6C synthesis may be used to prevent its accumulation benefiting PDE patients. Inhibition of the enzyme aminoadipic semialdehyde synthase, for example, could constitute a new strategy to treat PDE and other inherited diseases of lysine catabolism.

Effect of dietary lysine and genetics on growth and indices of lysine catabolism in rainbow trout (Oncorhynchus mykiss)

The level of the essential amino acid lysine is of concern in trout feed. The objective of this study was to investigate the response of different families of fish to lysine-deficient (LD) versus lysine-adequate (LA) soy protein-containing diets. For each treatment combination, there were five replicates. As expected, feed efficiency (p .05) of diet on hepatic lysine α-ketoglutarate reductase (LKR) activity, LKR mRNA abundance or lysine oxidation. There was a family effect on feed efficiency (p < .0001), TGC (p < .0001) and condition factor (p < .05) and there was a trend for differences in oxygen consumption (p < .07) across families while consuming the LD diet; however, there was no effect on ammonia excretion, HSI, lipid content, efficiency of nitrogen or lysine retention or indices of lysine catabolism. One family, in particular, had more favourable feed efficiency and thermal growth coefficient when fed the LD diet, indicating that it may possess an enhanced genetic potential for performance when consuming LD, soybean meal-containing diets.

Simultaneous detection of lysine metabolites by a single LC-MS/MS method: monitoring lysine degradation in mouse plasma.

Detection and quantification of lysine degradation metabolites in plasma is necessary for the diagnosis and follow-up of diseases such as pyridoxine-dependent epilepsy. The principal metabolites involved in the disease are related to the first steps of lysine oxidation, either through the saccharopine or the pipecolate pathways. Currently, there are three different analytical methods used to assess the content of these metabolites in urine and plasma, but they require different sample preparations and analytical equipment. Here, we describe a protocol that calls for a simple sample preparation and uses liquid chromatography tandem mass spectrometry (LC–MS/MS) that allows simultaneous detection and quantification of underivatized l-saccharopine, l-aminoadipic acid, l-pipecolic acid, piperideine-6-carboxylate, l-glutamic acid, and pyridoxal-5-phosphate in plasma samples. To validate the method we analyzed the time course degradation after intraperitoneal injection of l-lysine in C57BL/6/J mice. We observed that the degradation of lysine through the saccharopine pathway reached a maximum within the first 2 h. At this time point there was an increase in the levels of the metabolites saccharopine, aminoadipic acid, and pipecolic acid by 3-, 24- and 3.4-fold, respectively, compared to time zero levels. These metabolites returned to basal levels after 4–6 h. In conclusion, we have developed a LC–MS/MS approach, which allows simultaneous analysis of lysine degradation metabolites without the need for derivatization.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-1809-1) contains supplementary material, which is available to authorized users.

Selective Determination of Lysine in Dry-Cured Meats Using a Sensor Based on Lysine-α-Oxidase Immobilised on a Nylon Membrane

An enzymatic sensor employing lysine oxidase (LOx) with the immobilised enzyme system by crosslinking with glutaraldehyde using an immunodyne ABC nylon membrane, in combination with an oxygen electrode, has been optimised to determine the lysine content in dry-cured ham and dry-fermented sausage at different cured times. The amperometric signal obtained due to the oxygen depletion (consumed oxygen) during the lysine oxidation was recorded at 5 s in the immobilised enzyme sensor, and the reaction rates (slope) were related to the lysine content. A linear relationship between the consumed oxygen as a function of time (mg O2/l/s) and the lysine concentration in the range 10–250 μM (R 2 = 0.9946) for the immobilised enzyme system was found. The immobilised enzyme sensor showed a high specificity and sensibility. Nevertheless, the stability of the immobilised enzyme at the assay temperature was very poor, and thus, a new membrane was required for each analysis. The analysis of lysine with the immobilised enzyme system in cured meat samples revealed very good agreement with the determination performed through standard HPLC methodology, which validated the use of this sensor as an alternative technique to evaluate cured meat quality.

LOXL2 Oxidizes Methylated TAF10 and Controls TFIID-Dependent Genes during Neural Progenitor Differentiation

Protein function is often regulated and controlled by posttranslational modifications, such as oxidation. Although oxidation has been mainly considered to be uncontrolled and nonenzymatic, many enzymatic oxidations occur on enzyme-selected lysine residues; for instance, LOXL2 oxidizes lysines by converting the ε-amino groups into aldehyde groups. Using an unbiased proteomic approach, we have identified methylated TAF10, a member of the TFIID complex, as a LOXL2 substrate. LOXL2 oxidation of TAF10 induces its release from its promoters, leading to a block in TFIID-dependent gene transcription. In embryonic stem cells, this results in the inactivation of the pluripotency genes and loss of the pluripotent capacity. During zebrafish development, the absence of LOXL2 resulted in the aberrant overexpression of the neural progenitor gene Sox2 and impaired neural differentiation. Thus, lysine oxidation of the transcription factor TAF10 is a controlled protein modification and demonstrates a role for protein oxidation in regulating pluripotency genes.

Role of Phenolics Extracting from Rosa canina L. on Meat Protein Oxidation During Frozen Storage and Beef Patties Processing

Recent findings suggested that using frozen material for meat processing leads to products with increased protein oxidation rates and impaired quality traits. Therefore, the effects of frozen storage and the addition of a phenolic-rich dog rose extract (Rosa canina L.; RC), on lipid and protein oxidation, moisture losses, color stability, and hardness of beef patties were investigated. Protein oxidation was assessed by means of tryptophan loss and the formation of specific lysine oxidation products: α-aminoadipic semialdehyde (AAS), α-aminoadipic acid (AAA), and Schiff bases. Frozen storage increased proteins susceptibility towards oxidation during successive technological processes. The addition of the RC extract inhibited the formation of AAS, AAA, and had an antioxidant effect towards tryptophan oxidation, but promoted the formation of Schiff bases and incremented the hardness of beef patties. The antioxidant effect may be attributed to the phenolic compounds, mainly procyanidins, found on the RC extract. Further knowledge on the interactions between phenolics and proteins is needed to optimize the application of these antioxidants against meat protein oxidation.

Effects of Strain and Production-Cycle on Indices of Lysine Catabolism in Turkeys

In typical turkey production diets, lysine is frequently the second limiting amino acid. Understanding its catabolism could provide opportunities to increase the efficiency of lysine use for protein synthesis. We hypothesize that indices of lysine catabolism in turkey liver vary throughout the production cycle. Two commercial strains of turkey, Strain A and B, were analyzed 8 times over a period of 17 weeks (n = 8 birds/sampling time/strain) for lysine alpha-ketoglutarate (LKR) and saccharopine dehydrogenase (SDH) activities and mRNA abundance, in vitro lysine oxidation (LOX), L-amino acid oxidase (LAAO) activity, lysyl oxidase (LO) activity and mRNA expression of cationic amino acid transporters (CAT) 1, 2 and 3. We found differences in hepatic LKR activity (p = 0.007), LKR mRNA (p = 0.0004), SDH activity (p = 0.008), LOX (p<0.0001), lysyl oxidase activity (p<0.01), LAAO (p<0.0001) and CAT1 (p = 0.005) and 2 mRNA abundance (p = 0.0022) throughout the production cycle. We also found an effect of strain on SDH (p = 0.046) and CAT-2 mRNA abundance (p = 0.02); while no age or strain effects were detected for CAT3 mRNA abundance. Interestingly, the average LKR and SDH activities across strains and weeks was 240 and 420 nmol per minute per gram of liver, respectively, as opposed to the average LAAO activity, lysyl oxidase activity and L OX which were 0.70, 0.10 and 13.5 nmol per minute per gram liver, respectively. These data indicate that the saccharopine-dependent pathway is the predominant pathway of lysine degradation in turkey liver and that indices of hepatic lysine catabolism vary throughout the production cycle.