Capecitabine as a minor groove binder of DNA: molecular docking,molecular dynamics,and multi-spectroscopic studies

The interaction mechanism and binding mode of capecitabine with ctDNA was extensively investigated using docking and molecular dynamics simulations, fluorescence and circular dichroism (CD) spectroscopy, DNA thermal denaturation studies, and viscosity measurements. The possible binding mode and acting forces on the combination between capecitabine and DNA had been predicted through molecular simulation. Results indicated that capecitabine could relatively locate stably in the G-C base-pairs-rich DNA minor groove by hydrogen bond and several weaker nonbonding forces. Fluorescence spectroscopy and fluorescence lifetime measurements confirmed that the quenching was static caused by ground state complex formation. This phenomenon indicated the formation of a complex between capecitabine and ctDNA. Fluorescence data showed that the binding constants of the complex were approximately 2 × 10⁴ M^?1. Calculated thermodynamic parameters suggested that hydrogen bond was the main force during binding, which were consistent with theoretical results. Moreover, CD spectroscopy, DNA melting studies, and viscosity measurements corroborated a groove binding mode of capecitabine with ctDNA. This binding had no effect on B-DNA conformation.     

Binding of Janus kinase inhibitor tofacitinib with human serum albumin: multi-technique approach

In this report, we have investigated the binding affinity of tofacitinib with human serum albumin (HSA) under simulated physiological conditions by using UV–visible spectroscopy, fluorescence quenching measurements, dynamic light scattering (DLS), differential scanning calorimetry (DSC) and molecular docking methods. The obtained results demonstrate that fluorescence intensity of HSA gets quenched by tofacitinib and quenching occurs in static manner. Binding parameters calculated from modified Stern–Volmer equation shows that the drug binds to HSA with a binding constant in the order of 10⁵. Synchronous fluorescence data deciphered the change in the microenvironment of tryptophan residue in HSA. UV spectroscopy and DLS measurements deciphered complex formation and reduction in hydrodynamic radii of the protein, respectively. Further DSC results show that tofacitinib increases the thermo stability of HSA. Hydrogen bonding and hydrophobic interaction are the main binding forces between HSA and tofacitinib as revealed by docking results.     

Spectroscopic investigation and in vitro cytotoxic activity toward HepG2 cells of a copper compound complexed with human serum albumin

The human serum albumin (HSA) interaction of a mixed‐ligand copper compound (1) with an imidazole and taurine Schiff base derived from salicylaldehyde and taurine was investigated using fluorescence spectroscopy, UV–vis spectroscopy, time‐resolved fluorescence spectroscopy, circular dichroism (CD) spectroscopy, Fourier transform infrared (FT‐IR) spectroscopy and a molecular docking technique. The results of fluorescence and time‐resolved fluorescence spectroscopy indicated that 1 can effectively quench the HSA fluorescence by a static mechanism. Binding constants (K) and the number of binding sites (n ≈ 1) were calculated using modified Stern–Volmer equations. The thermodynamic parameters were calculated. UV–vis, CD and FT‐IR spectroscopy measurements confirm the alterations in the HSA secondary structure induced by 1. The site marker competitive experiment confirms that 1 is located in subdomain IB of HSA. The combination of molecular docking results and fluorescence experimental results reveal that hydrophobic interaction and hydrogen bonds are the predominant intermolecular forces stabilizing the 1–HSA complex. The 1–HSA complex increases approximately three times its cytotoxicity in cancer cells but has no effect on normal cells in vitro. Compared with unbound 1, the 1–HSA complex promotes HepG2 cells apoptosis and also has a stronger capacity for cell cycle arrest at the S phase of HepG2 cells.     

Synthesis,Characterization, and Cytotoxicity Studies of a Novel Palladium(II) Complex and Evaluation of DNA-Binding Aspects

A new water-soluble palladium(II) complex, [Pd(bpy)(pyr-Ac]NO₃ in which bpy = 2,2′-bipyridine and pyr-Ac is 1-pyrrolacetato, has been synthesized and characterized by spectroscopic methods (¹H NMR, FT-IR, and UV-Vis), molar conductivity measurements, and elemental analysis. The results obtained from elemental analysis and conductivity measurements confirmed the stoichiometry of ligand and its complex while the characteristic peaks in UV-Vis and FT-IR and resonance peaks in ¹H NMR spectra confirmed the formation of ligand frameworks around the palladium ion. The 50% cytotoxic concentration (Ic₅₀) of new synthesized Pd(II) complex was determined by using MTT assay against human breast cancer cell line, T47D. The interaction between the Pd(II) complex with calf thymus DNA was studied at different temperatures by using absorption spectroscopy, fluorescence titration spectra, ethidium bromide displacement, and gel chromatography studies. The results obtained by absorption spectroscopy revealed that the Pd(II) complex can bind to DNA cooperatively at low concentrations. Several binding parameters in the above interaction were calculated by the fluorescence quenching method. The quenching mechanism was suggested to be the static quenching. The thermodynamic parameters: enthalpy change (ΔH °), entropy change (ΔS °), and Gibbs free energy (ΔG °), showed that van der Waals and hydrogen binding are predominant intermolecular forces between Pd(II) complex and DNA. These results were also consistent with the results obtained from Scatchard's plots.     

Comparison of interactions between human serum albumin and silver nanoparticles of different sizes using spectroscopic methods

Three different sizes (15.9 ± 2.1 nm, 26.4 ± 3.2 nm and 39.8 ± 4.0 nm, respectively) of citrate‐coated silver nanoparticles (SNPs) have been synthesized and characterized. The interactions of the synthesized SNPs with human serum albumin (HSA) at physiological pH have been systematically studied by UV‐vis absorption spectroscopy, fluorescence spectroscopy, synchronous fluorescence spectroscopy, three‐dimensional fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The results indicate that the SNPs can bind to HSA with high affinity and quench the intrinsic fluorescence of HSA. The binding constants and quenching rate constants were calculated. The apparent association constants (K_app) values are 2.14 × 10⁴ M^–1 for 15.9 nm SNP, 1.65 × 10⁴ M^–1 for 26.4 nm SNP and 1.37 × 10⁴ M^–1 for 39.8 nm SNP, respectively. The values of binding constant obtained from the fluorescence quenching data match well with that determined from the absorption spectral changes. These results suggest that the smaller SNPs have stronger interactions to HSA than the larger ones at the same concentrations. Synchronous fluorescence, three‐dimensional fluorescence and CD spectroscopy studies show that the synthesized SNPs can induce slight conformational changes in HSA. Copyright © 2014 John Wiley & Sons, Ltd.     

Molecular docking and spectroscopic studies on the interaction of new fifth-generation antibacterial drug ceftobiprole with calf thymus DNA

Abstract

The interaction of the cefobiprole drug with calf thymus DNA (ct-DNA) at physiological pH was investigated by UV-visible spectrophotometry, fluorescence measurement, dynamic viscosity measurements, circular dichroism spectroscopy and molecular modeling. The binding constant obtained of UV–visible was 4?×?10⁴ L mol^?1. Moreover, the results of circular dichroism (CD) and viscosity measurements displayed that the binding of the cefobiprole to ct-DNA can change the conformation of ct-DNA. Furthermore, thermodynamic parameters indicated that hydrogen bond and van der waals play main roles in the binding of cefobiprole to ct-DNA. Optimal results of docking, it can be concluded that ceftobiprole-DNA docked model is in approximate correlation with our experimental results.     

In vitro study on binding interaction of quinapril with bovine serum albumin (BSA) using multi-spectroscopic and molecular docking methods

The binding interaction between quinapril (QNPL) and bovine serum albumin (BSA) in vitro has been investigated using UV absorption spectroscopy, steady-state fluorescence spectroscopic, synchronous fluorescence spectroscopy, 3D fluorescence spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and molecular docking methods for obtaining the binding information of QNPL with BSA. The experimental results confirm that the quenching mechanism of the intrinsic fluorescence of BSA induced by QNPL is static quenching based on the decrease in the quenching constants of BSA in the presence of QNPL with the increase in temperature and the quenching rates of BSA larger than 10¹⁰ L mol^?1 s^?1, indicating forming QNPL–BSA complex through the intermolecular binding interaction. The binding constant for the QNPL–BSA complex is in the order of 10⁵ M^?1, indicating there is stronger binding interaction of QNPL with BSA. The analysis of thermodynamic parameters together with molecular docking study reveal that the main binding forces in the binding process of QNPL with BSA are van der Waal’s forces and hydrogen bonding interaction. And, the binding interaction of BSA with QNPL is an enthalpy-driven process. Based on Förster resonance energy transfer, the binding distance between QNPL and BSA is calculated to be 2.76 nm. The results of the competitive binding experiments and molecular docking confirm that QNPL binds to sub-domain IIA (site I) of BSA. It is confirmed there is a slight change in the conformation of BSA after binding QNPL, but BSA still retains its secondary structure α-helicity.     

Evaluation of Metabolomic Changes as a Biomarker of Chondrogenic Differentiation in 3D-cultured Human Mesenchymal Stem Cells Using Proton (1H) Nuclear Magnetic Resonance Spectroscopy

Purpose

The purpose of this study was to evaluate the metabolomic changes in 3D-cultured human mesenchymal stem cells (hMSCs) in alginate beads, so as to identify biomarkers during chondrogenesis using ¹H nuclear magnetic resonance (NMR) spectroscopy.

Materials and Methods

hMSCs (2×10⁶ cells/mL) were seeded into alginate beads, and chondrogenesis was allowed to progress for 15 days. NMR spectra of the chondrogenic hMSCs were obtained at 4, 7, 11, and 15 days using a 14.1-T (600-MHz) NMR with the water suppression sequence, zgpr. Real-Time polymerase chain reaction (PCR) was performed to confirm that that the hMSCs differentiated into chondrocytes and to analyze the metabolomic changes indicated by the NMR spectra.

Results

During chondrogenesis, changes were detected in several metabolomes as hMSC chondrogenesis biomarkers, e.g., fatty acids, alanine, glutamate, and phosphocholine. The metabolomic changes were compared with the Real-Time PCR results, and significant differences were determined using statistical analysis. We found that changes in metabolomes were closely related to biological reactions that occurred during the chondrogenesis of hMSCs.

Conclusions

In this study, we confirm that metabolomic changes detected by ¹H-NMR spectroscopy during chondrogenic differentiation of 3D-cultured hMSCs in alginate beads can be considered as biomarkers of stem cell differentiation.     

Multi-spectroscopic,thermodynamic and molecular docking studies to investigate the interaction of eplerenone with human serum albumin

The binding of small molecular drugs with human serum albumin (HSA) has a crucial influence on their pharmacokinetics. The binding interaction between the antihypertensive eplerenone (EPL) and HSA was investigated using multi-spectroscopic techniques for the first time. These techniques include ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR), native fluorescence spectroscopy, synchronous fluorescence spectroscopy and molecular docking approach. The fluorescence spectroscopic study showed that EPL quenched HSA inherent fluorescence. The mechanism for quenching of HSA by EPL has been determined to be static in nature and confirmed by UV absorption and fluorescence spectroscopy. The modified Stern–Volmer equation was used to estimate the binding constant (K_b) as well as the number of bindings (n). The results indicated that the binding occurs at a single site (K_b = 2.238 × 10³ L mol⁻¹at 298 K). The enthalpy and entropy changes (∆H and ∆S) were 58.061 and 0.258 K J mol⁻¹, respectively, illustrating that the principal intermolecular interactions stabilizing the EPL–HSA system are hydrophobic forces. Synchronous fluorescence spectroscopy revealed that EPL binding to HSA occurred around the tyrosine (Tyr) residue and this agreed with the molecular docking study. The Förster resonance energy transfer (FRET) analysis confirmed the static quenching mechanism. The esterase enzyme activity of HSA was also evaluated showing its decrease in the presence of EPL. Furthermore, docking analysis and site-specific markers experiment revealed that EPL binds with HSA at subdomain IB (site III).     

Predicting total, abdominal, visceral and hepatic adiposity with circulating biomarkers in caucasian and Japanese american women

Background

Characterization of abdominal and intra-abdominal fat requires imaging, and thus is not feasible in large epidemiologic studies.

Objective

We investigated whether biomarkers may complement anthropometry (body mass index [BMI], waist circumference [WC], and waist-hip ratio [WHR]) in predicting the size of the body fat compartments by analyzing blood biomarkers, including adipocytokines, insulin resistance markers, sex steroid hormones, lipids, liver enzymes and gastro-neuropeptides.

Methods

Fasting levels of 58 blood markers were analyzed in 60 healthy, Caucasian or Japanese American postmenopausal women who underwent anthropometric measurements, dual energy X-ray absorptiometry (DXA), and abdominal magnetic resonance imaging. Total, abdominal, visceral and hepatic adiposity were predicted based on anthropometry and the biomarkers using Random Forest models.

Results

Total body fat was well predicted by anthropometry alone (R² = 0.85), by the 5 best predictors from the biomarker model alone (leptin, leptin-adiponectin ratio [LAR], free estradiol, plasminogen activator inhibitor-1 [PAI1], alanine transaminase [ALT]; R² = 0.69), or by combining these 5 biomarkers with anthropometry (R² = 0.91). Abdominal adiposity (DXA trunk-to-periphery fat ratio) was better predicted by combining the two types of predictors (R² = 0.58) than by anthropometry alone (R² = 0.53) or the 5 best biomarkers alone (25(OH)-vitamin D₃, insulin-like growth factor binding protein-1 [IGFBP1], uric acid, soluble leptin receptor [sLEPR], Coenzyme Q10; R² = 0.35). Similarly, visceral fat was slightly better predicted by combining the predictors (R² = 0.68) than by anthropometry alone (R² = 0.65) or the 5 best biomarker predictors alone (leptin, C-reactive protein [CRP], LAR, lycopene, vitamin D₃; R² = 0.58). Percent liver fat was predicted better by the 5 best biomarker predictors (insulin, sex hormone binding globulin [SHBG], LAR, alpha-tocopherol, PAI1; R² = 0.42) or by combining the predictors (R² = 0.44) than by anthropometry alone (R² = 0.29).

Conclusion

The predictive ability of anthropometry for body fat distribution may be enhanced by measuring a small number of biomarkers. Studies to replicate these data in men and other ethnic groups are warranted.     

Insights into the binding interaction between copper ferrite nanoparticles and bovine serum albumin: An effect on protein conformation and activity

The binding affinity between bovine serum albumin (BSA) and copper ferrite (CuFe₂O₄) nanoparticles in terms of conformation, stability and activity of protein was studied using various spectroscopic methods. The quenching involved in BSA–CuFe₂O₄ NP interaction was static quenching as analysed by different techniques (steady‐state and time‐resolved fluorescence along with temperature‐dependent fluorescence measurements). Among all types of possible interactions, it was revealed that the major binding forces were van der Waals interaction and hydrogen bonding, which were explored from negative values of enthalpy change (?H = ?193.85 kJ mol^?1) and entropy change (?S = ?588.88 J mol^?1 K^?1). Additionally, synchronous, circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy measurements confirmed the conformational changes in BSA upon the addition of CuFe₂O₄ NP. Furthermore, thermal denaturation observations were consistent with the circular dichroism results. The interaction of CuFe₂O₄ NP with BSA decreased the esterase activity in the BSA assay, revealing the affinity of copper ferrite towards the active site of BSA.     

Combining time‐resolved fluorescence with synchronous fluorescence spectroscopy to study bovine serum albumin‐curcumin complex during unfolding and refolding processes

We investigated the complex interaction between bovine serum albumin (BSA) and curcumin by combining time‐resolved fluorescence and synchronous fluorescence spectroscopy. The interaction was significant and sensitive to fluorescence lifetime and synchronous fluorescence characteristics. Binding of curcumin significantly shortened the fluorescence lifetime of BSA with a bi‐molecular quenching rate constant of k_q = 3.17 × 10¹² M^‐1s^‐1. Denaturation by urea unfolded the protein molecule by quenching the fluorescence lifetime of BSA. The tyrosine synchronous fluorescence spectra were blue shifted whereas the position of tryptophan synchronous fluorescence spectra was red shifted during the unfolding process. However, denaturation of urea had little effect on the synchronous fluorescence peak of tyrosine in curcumin‐BSA complex except in the low concentration range; however, it shifted the peak to the red, indicating that curcumin shifted tryptophan moiety to a more polar environment in the unfolded state. Decreases in the time‐resolved fluorescence lifetime and curcumin‐BSA complex during unfolding were recovered during refolding of BSA by a dilution process, suggesting partial reversibility of the unfolding process for both BSA and curcumin‐BSA complex. Copyright © 2012 John Wiley & Sons, Ltd.     

Insights into In Vitro Binding of Parecoxib to Human Serum Albumin by Spectroscopic Methods

Herein, we report the effect of parecoxib on the structure and function of human serum albumin (HSA) by using fluorescence, circular dichroism (CD), Fourier transforms infrared (FTIR), three‐dimensional (3D) fluorescence spectroscopy, and molecular docking techniques. The Stern–Volmer quenching constants K_SV and the corresponding thermodynamic parameters ΔH, ΔG, and ΔS have been estimated by the fluorescence quenching method. The results indicated that parecoxib binds spontaneously with HSA through van der Waals forces and hydrogen bonds with binding constant of 3.45 × 10⁴ M^?1 at 298 K. It can be seen from far‐UV CD spectra that the α‐helical network of HSA is disrupted and its content decreases from 60.5% to 49.6% at drug:protein = 10:1. Protein tertiary structural alterations induced by parecoxib were also confirmed by FTIR and 3D fluorescence spectroscopy. The molecular docking study indicated that parecoxib is embedded into the hydrophobic pocket of HSA.     

Combined spectroscopies and molecular docking approach to characterizing the binding interaction of enalapril with bovine serum albumin

The binding interaction between bovine serum albumin (BSA) and enalapril (ENPL) at the imitated physiological conditions (pH = 7.4) was investigated using UV–vis absorption spectroscopy (UV–vis), fluorescence emission spectroscopy (FES), synchronous fluorescence spectroscopy (SFS), Fourier transform infrared spectroscopy (FT‐IR), circular dichroism (CD) and molecular docking methods. It can be deduced from the experimental results from the steady‐state fluorescence spectroscopic titration that the intrinsic BSA fluorescence quenching mechanism induced by ENPL is static quenching, based on the decrease in the BSA quenching constants in the presence of ENPL with increase in temperature and BSA quenching rates >10¹⁰ L mol^?1 sec^?1. This result indicates that the ENPL–BSA complex is formed through an intermolecular interaction of ENPL with BSA. The main bonding forces for interaction of BSA and ENPL are van der Waal's forces and hydrogen bonding interaction based on negative values of Gibbs free energy change (ΔG ⁰), enthalpic change (ΔH ⁰) and entropic change (ΔS ⁰). The binding of ENPL with BSA is an enthalpy‐driven process due to |ΔH °| > |T ΔS °| in the binding process. The results of competitive binding experiments and molecular docking confirm that ENPL binds in BSA sub‐domain IIA (site I) and results in a slight change in BSA conformation, but BSA still retains its α‐helical secondary structure.     

Probing the behavior of bovine serum albumin upon binding to atenolol: insights from spectroscopic and molecular docking approaches

Molecular interaction of atenolol, a selective β₁ receptor antagonist with the major carrier protein, bovine serum albumin (BSA), was investigated under imitated physiological conditions (pH 7.4) by means of fluorescence spectroscopy, UV absorption spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and molecular modeling studies. The steady-state fluorescence spectra manifested that static type, due to formation of the atenolol-BSA complex, was the dominant mechanism for fluorescence quenching. The characteristic information about the binding interaction of atenolol with BSA in terms of binding constant (K_b) were determined by the UV–vis absorption titration, and were found to be in the order of 10³ M^?1 at different temperatures, indicating the existence of a weak binding in this system. Thermodynamic analysis revealed that the binding process was primarily mediated by van der Waals force and hydrogen bonds due to the negative sign for enthalpy change (ΔH⁰), entropy change (ΔS⁰). The molecular docking results elucidated that atenolol preferred binding on the site II of BSA according to the findings observed in competitive binding experiments. Moreover, via alterations in synchronous fluorescence, three-dimensional fluorescence and FT-IR spectral properties, it was concluded that atenolol could arouse slight configurational and micro-environmental changes of BSA.     

Intrinsic fluorescence as a probe of structure-function relationships in Ca2+-transport ATPases

Applications of intrinsic fluorescence measurements in the study of Ca²⁺-transport ATPases are reviewed. Since the initial reports showing that the fluorescence emission was sensitive to Ca²⁺ binding, a substantial amount of work has focused on the use of both steady-state and time-resolved fluorescence spectroscopy to investigate structure-function relationships in sarcoplasmic reticulum and plasma membrane Ca²⁺-ATPases. These studies have revealed ligand-induced conformational changes, as well as provided information on protein-protein, protein-solvent and/or protein-lipid interactions in different functional states of these proteins. The main results of these studies, as well as possible future prospects are discussed.     

Laser spectroscopy measurements of the effective temperature of argon ions in the PNX-U plasma neutralizer

Laser spectroscopy measurements of the effective temperature of Ar¹⁺ ions in the PNX-U multipole trap, in which argon plasma is ionized and heated by microwaves under electron-cyclotron-resonance conditions, are performed using a narrow-band tunable dye laser. The absorption profile of the 611.5-nm line is examined. In a microwave power range of 5–50 kW, the observed behavior of the effective temperature of argon ions T_{i, eff} indicates an anomalous mechanism for ion heating. It is shown that certain information about the electron temperature can be deduced from measurements by the laser-induced fluorescence (LIF) technique. The measurements performed also serve to test the laser technique and apparatus that is presently being developed for diagnosing additives to the ITER divertor plasma by the LIF method.     

Combined spectroscopies and molecular docking approach to characterizing the binding interaction between lisinopril and bovine serum albumin

To further understand the mode of action and pharmacokinetics of lisinopril, the binding interaction of lisinopril with bovine serum albumin (BSA) under imitated physiological conditions (pH 7.4) was investigated using fluorescence emission spectroscopy, synchronous fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD) and molecular docking methods. The results showed that the fluorescence quenching of BSA near 338 nm resulted from the formation of a lisinopril–BSA complex. The number of binding sites (n) for lisinopril binding on subdomain IIIA (site II) of BSA and the binding constant were ~ 1 and 2.04 × 10⁴ M^–1, respectively, at 310 K. The binding of lisinopril to BSA induced a slight change in the conformation of BSA, which retained its α‐helical structure. However, the binding of lisinopril with BSA was spontaneous and the main interaction forces involved were van der Waal's force and hydrogen bonding interaction as shown by the negative values of ΔG⁰, ΔH⁰ and ΔS⁰ for the binding of lisinopril with BSA. It was concluded from the molecular docking results that the flexibility of lisinopril also played an important role in increasing the stability of the lisinopril–BSA complex. Copyright © 2015 John Wiley & Sons, Ltd.     

Simultaneous Steady-state and Dynamic 13C NMR Can Differentiate Alternative Routes of Pyruvate Metabolism in Living Cancer Cells

Metabolic reprogramming facilitates cancer cell growth, so quantitative metabolic flux measurements could produce useful biomarkers. However, current methods to analyze flux in vivo provide either a steady-state overview of relative activities (infusion of ¹³C and analysis of extracted metabolites) or a dynamic view of a few reactions (hyperpolarized ¹³C spectroscopy). Moreover, although hyperpolarization has successfully quantified pyruvate-lactate exchanges, its ability to assess mitochondrial pyruvate metabolism is unproven in cancer. Here, we combined ¹³C hyperpolarization and isotopomer analysis to quantify multiple fates of pyruvate simultaneously. Two cancer cell lines with divergent pyruvate metabolism were incubated with thermally polarized [3-¹³C]pyruvate for several hours, then briefly exposed to hyperpolarized [1-¹³C]pyruvate during acquisition of NMR spectra using selective excitation to maximize detection of H[¹³C]O₃⁻ and [1-¹³C]lactate. Metabolites were then extracted and subjected to isotopomer analysis to determine relative rates of pathways involving [3-¹³C]pyruvate. Quantitation of hyperpolarized H[¹³C]O₃⁻ provided a single definitive metabolic rate, which was then used to convert relative rates derived from isotopomer analysis into quantitative fluxes. This revealed that H[¹³C]O₃⁻ appearance reflects activity of pyruvate dehydrogenase rather than pyruvate carboxylation followed by subsequent decarboxylation reactions. Glucose substantially altered [1-¹³C]pyruvate metabolism, enhancing exchanges with [1-¹³C]lactate and suppressing H[¹³C]O₃⁻ formation. Furthermore, inhibiting Akt, an oncogenic kinase that stimulates glycolysis, reversed these effects, indicating that metabolism of pyruvate by both LDH and pyruvate dehydrogenase is subject to the acute effects of oncogenic signaling on glycolysis. The data suggest that combining ¹³C isotopomer analyses and dynamic hyperpolarized ¹³C spectroscopy may enable quantitative flux measurements in living tumors.     

Synchrotron-excited time-resolved fluorescence spectroscopy of adenosine,protonated adenosine and 6N, 6N-dimethyladenosine in aqueous solution at room temperature

The fluorescence behavior of adenosine in neutral solution has been studied by time-resolved spectroscopy using synchrotron excitation and timecorrelated single photon counting, and by decay time measurements. Three emissions have been identified and correlated with three excitation spectra. The assignment of these transitions has been made by comparison with similar measurements on ⁶N, ⁶N-dimethyladenosine (6 DMA), and on adenosine in acid solution (ADO H⁺). It is proposed that two of the transitions of adenosine which correlate with 6DMA originate from coplanar and orthogonal rotational conformers of the amino group. The other transition, correlating with ADO H⁺ may originate either from the ³H-imino tautomer, or from a differently solvated rotational conformer.A partial presentation of this work has been made at the Second Congress of the European Society for Photobiology Padova, Italy, 6–10 September 1987