Transfer Of Amino Group Research Articles

Abnormally Low Alanine Aminotransferase Ameliorated by a Living Donor Liver Transplantation: A Case Report

Alanine aminotransferase (ALT) is an enzyme that catalyzes the transfer of amino groups from alanine to ketoglutaric acid. ALT is an established marker of liver diseases. Occasionally, ALT levels may be abnormally low due to various factors, making accurate assessment difficult. To date, no studies have documented ALT alterations following Living donor liver transplantation (LDLT) in patients with low ALT levels. Here, we present a case of abnormally low ALT levels that were ameliorated by LDLT. A 27-year-old woman underwent LDLT for refractory cholangitis with biliary atresia. The patient's preoperative ALT level was 1 IU/L. Following graft reperfusion, ALT levels increased (peak value, 456 IU/L), primarily attributed to the donor liver. After LDLT, ALT levels consistently surpassed the lower limit. The differential diagnosis of abnormally low ALT levels suggested a genetic mutation as the most probable underlying cause. Even after LDLT, ALT levels in organs other than the transplanted liver would remain abnormally low. Therefore, to prevent underestimating liver damage, the standard ALT range for such cases should be set lower than the typical range.

Free Amino Group Transfer via α-Amination of Native Carbonyls.

We report herein a straightforward transfer of a free amino group (NH2 ) from a commercially available nitrogen source to unfunctionalized, native carbonyls (amides and ketones) resulting in direct α-amination. Primary α-amino carbonyls are readily produced under mild conditions, further enabling diverse in situ functionalization reactions-including peptide coupling and Pictet-Spengler cyclization-that capitalize on the presence of the unprotected primary amine.

Transfer freier Aminogruppen via α-Aminierung von Carbonylen.

AbstractEine Strategie zur direkten α‐Aminierung unfunktionalisierter Carbonylverbindungen wird berichtet. Unter Verwendung einer kommerziell verfügbaren Stickstoffquelle zur Übertragung der freien Aminogruppe (NH2) werden primäre α‐Aminocarbonylverbindungen unter besonders milden Bedingungen hergestellt. Die direkte Einführung einer ungeschützten, primären Aminogruppe ermöglicht in der Folge zahlreiche in situ Funktionalisierungen der erhaltenen Reaktionsprodukte, einschließlich Peptidkupplungen und Pictet–Spengler Cyclisierungen.

Crystal Structure and Functional Characterization of Acetylornithine Aminotransferase from Corynebacterium glutamicum.

The amino acids l-arginine and l-ornithine are widely used in animal feed and as health supplements and pharmaceutical compounds. In arginine biosynthesis, acetylornithine aminotransferase (AcOAT) uses pyridoxal-5'-phosphate (PLP) as a cofactor for amino group transfer. Here, we determined the crystal structures of the apo and PLP complex forms of AcOAT from Corynebacterium glutamicum (CgAcOAT). Our structural observations revealed that CgAcOAT undergoes an order-to-disorder conformational change upon binding with PLP. Additionally, we observed that unlike other AcOATs, CgAcOAT exists as a tetramer. Subsequently, we identified the key residues involved in PLP and substrate binding based on structural analysis and site-directed mutagenesis. This study might provide structural insights on CgAcOAT, which can be utilized for the development of improved l-arginine production enzymes.

Prebiotic Synthesis of Aspartate Using Life's Metabolism as a Guide.

A protometabolic approach to the origins of life assumes that the conserved biochemistry of metabolism has direct continuity with prebiotic chemistry. One of the most important amino acids in modern biology is aspartic acid, serving as a nodal metabolite for the synthesis of many other essential biomolecules. Aspartate's prebiotic synthesis is complicated by the instability of its precursor, oxaloacetate. In this paper, we show that the use of the biologically relevant cofactor pyridoxamine, supported by metal ion catalysis, is sufficiently fast to offset oxaloacetate's degradation. Cu2+-catalysed transamination of oxaloacetate by pyridoxamine achieves around a 5% yield within 1 h, and can operate across a broad range of pH, temperature, and pressure. In addition, the synthesis of the downstream product β-alanine may also take place in the same reaction system at very low yields, directly mimicking an archaeal synthesis route. Amino group transfer supported by pyridoxal is shown to take place from aspartate to alanine, but the reverse reaction (alanine to aspartate) shows a poor yield. Overall, our results show that the nodal metabolite aspartate and related amino acids can indeed be synthesised via protometabolic pathways that foreshadow modern metabolism in the presence of the simple cofactor pyridoxamine and metal ions.

Salivary Aspartate Aminotransferase, Alanine Aminotransferase and IgA as biomarkers for Type I Diabetes Mellitus: A Systematic Review

Introduction: Type I diabetes mellitus (T1DM) is an autoimmune disorder characterized by absolute insulin deficiency, which is caused by progressive destruction of the β-islet cells of the pancreas. Aminotransferases participate in the interconversion of amino acids and oxalic acids by transfer of amino groups. Organ damage leads to leakage of transaminases into the blood. IgA is the only immunoglobulin that is found in saliva and forms the first line of defense. Alteration in the levels of secretory IgA often indicates a local or systemic disease. The aim of this systematic review is to evaluate the role of salivary aspartate aminotransferase (AST), alanine aminotransferase (ALT), and IgA as biomarkers for T1DM patients. Materials and Methods: An electronic literature search was conducted by two independent reviewers using PubMed, Medline and Google scholar without any date filter. The inclusion criteria included case control and cross-sectional studies. Publications in languages other than English, review articles, letters to the editor, and studies done on animal models were excluded from the review. The difference in the levels of salivary AST, ALT, or IgA in T1DM patients and in healthy individuals were compared. Risk of bias assessment was done using the ROBINS-I tool. Results: A total of eight relevant articles were assessed, out of which three studies showed elevated salivary AST and ALT levels and five studies showed elevated salivary IgA levels in patients with T1DM. Conclusion: Our review reflected that salivary AST, ALT, and IgA were elevated in T1DM patients, and they can be used for monitoring these patients. Further studies are needed to establish the diagnostic accuracy of these parameters for clinical application.

PERBANDINGAN AKTIVITAS ENZIM ASPARTAT AMINOTRANSFERASE ANTARA SERUM YANG HEMOLISIS DAN SERUM NORMAL DENGAN METODE KINETIK-IFCC

Aspartic aminotransferase (AST) is a mitochondrial enzyme that catalyzes the back and forth transfer of amino groups from aspartic acid to ?-oxaloacetic acid to form glutamic acid and oxaloacetic acid. AST is contained in erythrocytes so that if there is hemolysis, a ruptured erythrocyte will cause an increase in the activity of the AST enzyme that comes out of the erythrocyte. This study aims to determine the effect of hemolysis in serum on AST enzyme activity. This research method is experimental by comparing normal serum with hemolytic serum. The research sample involved 30 employees of the Manding Sumenep Public Health Center who would be examined for the AST enzyme activity. The results showed that the AST enzyme activity in normal serum had an average of 24.367 IU / L, while the average hemolytic serum was 39.3 IU / L. Based on the results of these data, it shows that there is an increase in AST enzyme activity in hemolytic serum compared to normal serum.

Metals can catalyze amino acid synthesis

Amino acids are fundamental to living organisms because they combine to build proteins, the cell’s workhorses. One metabolic pathway to amino acids involves transamination, a reaction in which an amino group is transferred to a keto acid. Normally, an enzyme or cofactor catalyzes transamination. But Joseph Moran of the University of Strasbourg wondered whether this process happened without enzymes in the earliest days of life on Earth . At high temperatures, metal ions can catalyze transamination. A new study shows that metals that were likely abundant on early Earth can perform the catalysis under biological conditions ( J. Am. Chem. Soc. 2021, DOI: 10.1021/jacs.1c08535 ). The study’s top performers—those that produced the highest yield of amino acids—were copper, cobalt, vanadium, and nickel. Moran and his team analyzed how these metals catalyze the amino group transfer. “The metals essentially work in two different ways,” he says. Copper and cobalt stabilize an

Mechanistic Insight into Metal Ion-Catalyzed Transamination.

Several classes of biological reactions that are mediated by an enzyme and a co-factor can occur, to a slower extent, not only without the enzyme but even without the co-factor, under catalysis by metal ions. This observation has led to the proposal that metabolic pathways progressively evolved from using inorganic catalysts to using organocatalysts of increasing complexity. Transamination, the biological process by which ammonia is transferred between amino acids and α-keto acids, has a mechanism that has been well studied under enzyme/co-factor catalysis and under co-factor catalysis, but the metal ion-catalyzed variant was generally studied mostly at high temperatures (70-100°C), and the details of its mechanism remained unclear. Here, we investigate which metal ions catalyze transamination under conditions relevant to biology (pH 7, 20-50 °C) and study the mechanism in detail. Cu2+, Ni2+, Co2+, and V5+ were identified as the most active metal ions under these constraints. Kinetic, stereochemical, and computational studies illuminate the mechanism of the reaction. Cu2+ and Co2+ are found to predominantly speed up the reaction by stabilizing a key imine intermediate. V5+ is found to accelerate the reaction by increasing the acidity of the bound imine. Ni2+ is found to do both to a limited extent. These results show that direct metal ion-catalyzed amino group transfer is highly favored even in the absence of co-factors or protein catalysts under biologically compatible reaction conditions.

Surface modification of g-C3N4-supported iron catalysts for CO hydrogenation: Strategy for product distribution

Surface modified g-C3N4 supported iron catalysts were prepared using ultrasonic-assisted impregnation and employed as model catalysts to investigate the surface modification effects on product distribution in Fischer–Tropsch synthesis. Characterizations evidenced that both hydroxyl and amino groups were grafted on the g-C3N4 surface. Results showed that the selectivity of light olefins in hydrocarbons was increased from 12.3% on pure Fe3O4 to 31.5% on Fe/C3N4 further to 38.4% on Fe/AMC3N4 under same reaction condition as well as elevated activity owing to electron transfer of amino groups. But high CO2 selectivity was inevitable via the enhanced water gas shift reaction. H2O2 treatment increased the hydrophilicity of g-C3N4, resulting in predominance of water-assisted pathway promoted the chain growth. Compared with Fe/C3N4, the CH4 selectivity for Fe/OHC3N4 was significantly reduced from 38.4% to 22.8%. The Fe/OHC3N4 also exhibited lower CO2 selectivity of 11.4% than Fe/AMC3N4 of 24% due to the enrichment of surface hydroxyl. Surface modification played a critical role in tuning the product distribution and promoting the formation of light olefins with low C1 by products (CH4 and CO2).

Three-Dimensional Structure of Branched-Chain Amino Acid Transaminase from Thermoproteus uzoniensis in Complex with L-Norvaline

Transaminases (aminotransferases) are stereospecific enzymes catalyzing the reversible amino group transfer from various substrates. Transaminases are key enzymes in amino acid metabolism in all organisms, and they show promise for fine organic synthesis. Among a diversity of transaminases, as-yet poorly characterized pyridoxal 5′-phosphate-dependent fold type IV transaminases have attracted great interest. This transaminase family shows specificity for both D- and L-amino acids and (R)-amines. The crystal structure of thermally stable fold type IV branched-chain amino acid transaminase from the archaeon Thermoproteus uzoniensis in complex with the non-natural substrate L-norvaline was established. The mechanism of substrate binding is considered. The key amino acids involved in the substrate binding are described.

Modular Tuning of Electrophilic Reactivity of Iridium Nitrenoids for the Intermolecular Selective α-Amidation of β-Keto Esters.

We report herein an Ir-catalyzed intermolecular amino group transfer to β-keto esters (amides) to access α-aminocarbonyl products with excellent chemoselectivity. The key strategy was to engineer electrophilicity of the putative Ir-nitrenoids by tuning electronic property of the κ2-N,O chelating ligands, thus facilitating nucleophilic addition of enol π-bonds of 1,3-dicarbonyl substrates.

Functional characterization of aminotransferase involved in serine and aspartate metabolism in a halotolerant cyanobacterium, Aphanothece halophytica.

Aminotransferases catalyze the reversible pyridoxal phosphate-dependent transfer of amino groups from amino acids to oxo acids and play important roles for the balance between carbon and nitrogen metabolism. In this report, four aminotransferases (Ap1-Ap4) from a halotolerant cyanobacterium Aphanothece halophytica were examined. The results revealed that Ap1 and Ap2 exhibited the aspartate:2-oxoglutarate aminotransferase (AspAT) activity whereas Ap2 catalyzed further aminotransferase activities with alanine (AlaAT) and LL-diaminopimelate (an intermediate for the synthesis of Lys/peptidoglycan) as amino donors. Ap4 exhibited bifunctional aminotransferase with phosphoserine (PSAT) and glycine (GGAT) as amino donors. No activity was observed for Ap3. We identified third gene encoding phosphoserine phosphatase (PSP) in phosphorylate serine biosynthetic pathway. The levels of mRNA for Ap2 and ApMurE encoding UDP-N-acetylmuramoyl-L-alanyl-D-glutamate-2,6-diaminopimelate ligase were increased after salt stress. These results suggest the link among photorespiratory metabolite (serine, glycine, glyoxylate), phosphorylate serine biosynthetic pathway and aspartate metabolism via aminotransferases for the synthesis of peptidoglycan and betaine under salt stress conditions.

Asymmetric synthesis of l-phosphinothricin using thermostable alpha-transaminase mined from Citrobacter koseri

α-Transaminase (α-TA) responsible for catalyzing the reversible transfer of amino groups between amine donors and amine acceptors, is applicable to enzymatic route for asymmetric synthesis of herbicide l-phosphinothricin (l-PPT). In the search for α-TAs with better catalysis performance, three α-TAs were discovered by genome mining approach using a known sequence encoding Escherichia coli tyrosine TA (TyrB) as probe. Through detailed comparison of their expression amount, activities and characteristics, Citrobacter koseri TA (CkTA) exhibited better activity and thermostability, which retain 65.9% of initial activity after incubation at 57 °C for 4 h. The Km and kcat/Km values of CkTA were 36.75 mM and 34.29 mM−1 min−1, respectively. In addition, recombinant CkTA cells were immobilized onto Celite 545 using tris(hydroxymethyl)phosphine as crosslinker. During five repetitive asymmetric synthesis of l-PPT from 20 g/L prostereogenic ketone using l-Glu as amine donor, all the yields of l-PPT reached up to 91.2% (＞99% ee). These characteristics made CkTA a valuable addition to the currently scarce α-TA library for stereospecific synthesis of l-PPT.

Functional characterization of PLP fold type IV transaminase with a mixed type of activity from Haliangium ochraceum

Pyridoxal-5′-phosphate (PLP)-dependent transaminases are industrially important enzymes catalyzing the stereoselective amination of ketones and keto acids. Transaminases of PLP fold type IV are characterized by (R)- or (S)-stereoselective transfer of amino groups, depending on the substrate profile of the enzyme. PLP fold type IV transaminases include branched-chain amino acid transaminases (BCATs), D-amino acid transaminases and (R)-amine:pyruvate transaminases. Recently, transaminases with a mixed type of activity were identified and characterized. Here, we report biochemical and structural characterization of a transaminase from myxobacterium Haliangium ochraceum (Hoch3033), which is active towards keto analogs of branched-chain amino acids (specific substrates for BCATs) and (R)-(+)-α-methylbenzylamine (specific substrate for (R)-amine:pyruvate transaminases). The enzyme is characterized by an alkaline pH optimum (pH 10.0–10.5) and a tolerance to high salt concentrations (up to 2 M NaCl). The structure of Hoch3033 was determined at 2.35 Å resolution. The overall fold of the enzyme was similar to those of known enzymes of PLP fold type IV. The mixed type of activity of Hoch3033 was implemented within the BCAT-like active site. However, in the active site of Hoch3033, we observed substitutions of specificity-determining residues that are important for substrate binding in canonical BCATs. We suggest that these changes result in the loss of activity towards α-ketoglutarate and increase the affinity towards (R)-(+)-α-methylbenzylamine. These results complement our knowledge of the catalytic diversity of transaminases and indicate the need for further research to understand the structural basis of substrate specificity in these enzymes.

Non-Deprotonative Primary and Secondary Amination of (Hetero)Arylmetals.

Herein we disclose a novel method for the facile transfer of primary (-NH2) and secondary amino groups (-NHR) to heteroaryl- as well as arylcuprates at low temperature without the need for precious metal catalysts, ligands, excess reagents, protecting and/or directing groups. This one-pot transformation allows unprecedented functional group tolerance and it is well-suited for the amination of electron-rich, electron-deficient as well as structurally complex (hetero)arylmetals. In some of the cases, only catalytic amounts of a copper(I) salt is required.

Rapid heteroatom transfer to arylmetals utilizing multifunctional reagent scaffolds.

Arylmetals are highly valuable carbon nucleophiles that are readily and inexpensively prepared from aryl halides or arenes and widely used on both laboratory and industrial scales to react directly with a wide range of electrophiles. Although C-C bond formation has been a staple of organic synthesis, the direct transfer of primary amino (-NH2) and hydroxyl (-OH) groups to arylmetals in a scalable and environmentally friendly fashion remains a formidable synthetic challenge because of the absence of suitable heteroatom-transfer reagents. Here, we demonstrate the use of bench-stable N-H and N-alkyl oxaziridines derived from readily available terpenoid scaffolds as efficient multifunctional reagents for the direct primary amination and hydroxylation of structurally diverse aryl- and heteroarylmetals. This practical and scalable method provides one-step synthetic access to primary anilines and phenols at low temperature and avoids the use of transition-metal catalysts, ligands and additives, nitrogen-protecting groups, excess reagents and harsh workup conditions.

2-Aminobutyric acid modulates glutathione homeostasis in the myocardium.

A previous report showed that the consumption of glutathione through oxidative stress activates the glutathione synthetic pathway, which is accompanied by production of ophthalmic acid from 2-aminobutyric acid (2-AB). We conducted a comprehensive quantification of serum metabolites using gas chromatography-mass spectrometry in patients with atrial septal defect to find clues for understanding myocardial metabolic regulation, and demonstrated that circulating 2-AB levels reflect hemodynamic changes. However, the metabolism and pathophysiological role of 2-AB remains unclear. We revealed that 2-AB is generated by an amino group transfer reaction to 2-oxobutyric acid, a byproduct of cysteine biosynthesis from cystathionine. Because cysteine is a rate-limiting substrate for glutathione synthesis, we hypothesized that 2-AB reflects glutathione compensation against oxidative stress. A murine cardiomyopathy model induced by doxorubicin supported our hypothesis, i.e., increased reactive oxygen species are accompanied by 2-AB accumulation and compensatory maintenance of myocardial glutathione levels. Intriguingly, we also found that 2-AB increases intracellular glutathione levels by activating AMPK and exerts protective effects against oxidative stress. Finally, we demonstrated that oral administration of 2-AB efficiently raises both circulating and myocardial glutathione levels and protects against doxorubicin-induced cardiomyopathy in mice. This is the first study to demonstrate that 2-AB modulates glutathione homeostasis in the myocardium.

Structural role of two histidines in the (6-4) photolyase reaction.

Photolyases (PHRs) are DNA repair enzymes that revert UV-induced photoproducts, either cyclobutane pyrimidine dimers (CPD) or (6-4) photoproducts (PPs), into normal bases to maintain genetic integrity. (6-4) PHR must catalyze not only covalent bond cleavage, but also hydroxyl or amino group transfer, yielding a more complex mechanism than that postulated for CPD PHR. Previous mutation analysis revealed the importance of two histidines in the active center, H354 and H358 for Xenopus (6-4) PHR, whose mutations significantly lowered the enzymatic activity. Based upon highly sensitive FTIR analysis of the repair function, here we report that both H354A and H358A mutants of Xenopus (6-4) PHR still maintain their repair activity, although the efficiency is much lower than that of the wild type. Similar difference FTIR spectra between the wild type and mutant proteins suggest a common mechanism of repair in which (6-4) PP binds to the active center of each mutant, and is released after repair, as occurs in the wild type. Similar FTIR spectra also suggest that a decrease in volume by the H-to-A mutation is possibly compensated by the addition of water molecule( s). Such a modified environment is sufficient for the repair function that is probably controlled by proton-coupled electron transfer between the enzyme and substrate. On the other hand, two histidines must work in a concerted manner in the active center of the wild-type enzyme, which significantly raises the repair efficiency.

Aspartate Aminotransferase – Risk Marker for Type-2 Diabetes Mellitus or Red Herring?

Gamma glutamyltransferase (GGT), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) are common liver enzymes. Abnormal serum circulating levels of these enzymes may signal liver or cholestatic damage (1). Circulating GGT is present on the external surfaces of most cells, particularly hepatocytes, and is used as a biological marker of excessive alcohol intake (2). ALT and AST catalyze the transfer of amino groups to generate products in gluconeogenesis and amino acid metabolism (3, 4). Elevated serum levels of these aminotransferases signal acute or chronic liver injury (1). ALP is a hydrolase enzyme that transports metabolites across cell membranes, with elevated serum levels commonly used in clinical practice as a marker of liver or bony disease (1, 5). In addition to their physiological functions, a growing body of evidence indicates that baseline serum levels of these enzymes may be associated with the development of a wide range of disease outcomes. Several reports have indicated that among these enzymes, elevated baseline levels of GGT and ALT are each associated with increased risk of future type-2 diabetes mellitus (T2DM) (6, 7). Indeed, the associations are apparent even within normal ranges of these enzymes. There is, however, considerable uncertainty regarding the association between AST level and risk of T2DM. In a recent review, we synthesized available prospective epidemiological data on the association between AST and incident T2DM (7). The pooled analyses involving 1,912 incident T2DM cases did not show a significant association between AST and risk of future T2DM. In contrast, a recently rigorously conducted prospective study involving 2,182 incident T2DM cases, reported a multivariate adjusted relative risk (RR) of 1.16 (1.02–1.31) for T2DM in a comparison of the highest to the lowest quartile of baseline AST levels (8). The association was continuous and extended well within the normal range of AST levels. This large study adds to the growing body of evidence that like GGT and ALT, elevated AST level may also be associated with increased risk for T2DM. The prospective evidence on the association between AST and T2DM is inconclusive and this may be attributed to several reasons including: lack of adequate power, unmeasured confounding, or even over-adjustment for potential intermediates by previous studies. Given that levels of serum liver enzymes (GGT, ALT, and AST) (i) are strongly environmentally and genetically correlated with one another (9), and (ii) have shared genetic variances (10), the evidence is suggestive of common biological pathways affecting levels of these enzymes. There is therefore a possibility that the association between AST level and risk of T2DM might be mediated through the effects of the other liver enzymes. The potential impact of other liver enzymes on the AST–T2DM association is unclear as it is uncertain whether adjusting for such putative intermediates is appropriate. There are indications that further adjustment for other liver enzymes may be responsible for the substantially attenuated or null associations observed in several studies. To help clarify the evidence, we report an updated review.