Phe Uptake Research Articles

Effects of polystyrene microplastics on uptake and toxicity of phenanthrene in soybean

Microplastics (MPs) can influence the availability of contaminants in the soil and have adverse effects on plants. Up to now, the effects of MPs on the uptake of organic pollutants by leguminous plants are still unclear. In this study, we explored the impacts and mechanisms of polystyrene MPs of different sizes on the uptake of phenanthrene (Phe) by soybean seedlings. The results showed that MPs decreased the uptake of Phe in soybean roots and leaves. Micron-size MPs showed a higher inhibition of Phe uptake in roots than nano-size MPs (4.83 mg/kg) at the beginning with concentrations of 1.89 mg/kg, 3.40 mg/kg, and 0.72 mg/kg in groups 1 μm, 10 μm, and 100 μm MPs/Phe, respectively. The combined toxicity of micron-size MPs and Phe to soybean plants was higher than that of nano-size MPs and Phe, and 100 μm MPs and Phe co-contaminant show the highest toxicity to soybean. The activities of antioxidative enzymes and their gene expression showed that micron-size MPs induced higher genotoxic and oxidative damage to soybean roots than nano-size MPs, which decreased the activity of roots, thus leading to the lower uptake of Phe by soybean roots and leaves. This study highlights that the combined exposure to MPs and Phe causes harmful effects on soybean plants and MPs inhibit the uptake of organic pollutants by higher plants.

Different partition of polycyclic aromatic hydrocarbon on environmental particulates in freshwater: Microplastics in comparison to natural sediment

Microplastics pollution in the aquatic ecosystems has aroused increasing concerns in recent years. Though microplastics are known to sorb organic contaminants from water, the interaction mechanisms between microplastics and organic chemicals are not yet well understood. Here we investigated the partition characteristics of phenanthrene (Phe) in three mass-produced plastic particles, including polyethylene (PE), polystyrene (PS) and polyvinylchloride (PVC)， and one natural sediment, as a comparison. The sorption kinetics of Phe onto microplastics and natural sediment were successfully described by the pseudo-second-order model (R2 > 0.992), while the equilibrium data were best-fitted to the Langmuir isotherm (R2 > 0.995). Compared with natural sediment, microplastics exhibited higher capacities for Phe which followed an order of PE > PS > PVC. As the aqueous concentration of pyrene (Pyr) increased, both uptakes and distribution coefficients (Kd) of Phe within the solids decreased, with natural sediment giving the largest decline. Although proportions of Phe desorbed from the contaminated microplastics were low, due to the high Phe uptake, microplastics released larger amounts of the sorbed Phe to water than the natural sediment during the desorption process. Given their minimal abundance relative to natural sediment, microplastics may play a less important role in the transport of organic pollutants in a natural aquatic environment.

Phenylalanine as a nitrogen source induces root growth and nitrogen-use efficiency in Populus × canescens.

To investigate the physiological responses of poplars to amino acids as sole nitrogen (N) sources, Populus × canescens (Ait.) Smith plants were supplied with one of three nitrogen fertilizers (NH4NO3, phenylalanine (Phe) or the mixture of NH4NO3 and Phe) in sand culture. A larger root system, and decreased leaf size and CO2 assimilation rate was observed in Phe- versus NH4NO3-treated poplars. Consistently, a greater root biomass and a decreased shoot growth were detected in Phe-supplied poplars. Decreased enzymatic activities of nitrate reductase (NR), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) and elevated activities of nitrite reductase (NiR), phenylalanine ammonia lyase (PAL), glutamine synthetase (GS) and asparagine synthase (AS) were found in Phe-treated roots. Accordingly, reduced concentrations of NH4+, NO3- and total N, and enhanced N-use efficiencies (NUEs) were detected in Phe-supplied poplars. Moreover, the transcript levels of putative Phe transporters ANT1 and ANT3 were upregulated, and the mRNA levels of NR, glutamine synthetase 2 (GS2), NADH-dependent glutamate synthase (NADH-GOGAT), GDH and asparagine synthetase 2 (ASN2) were downexpressed in Phe-treated roots and/or leaves. The 15N-labeled Phe was mainly allocated in the roots and only a small amount of 15N-Phe was translocated to poplar aerial parts. These results indicate that poplar roots can acquire Phe as an N source to support plant growth and that Phe-induced NUEs in the poplars are probably associated with NH4+ re-utilization after Phe deamination and the carbon bonus simultaneously obtained during Phe uptake.

Quantifying the relative contributions of different solute carriers to aggregate substrate transport

Determining the contributions of different transporter species to overall cellular transport is fundamental for understanding the physiological regulation of solutes. We calculated the relative activities of Solute Carrier (SLC) transporters using the Michaelis-Menten equation and global fitting to estimate the normalized maximum transport rate for each transporter (Vmax). Data input were the normalized measured uptake of the essential neutral amino acid (AA) L-leucine (Leu) from concentration-dependence assays performed using Xenopus laevis oocytes. Our methodology was verified by calculating Leu and L-phenylalanine (Phe) data in the presence of competitive substrates and/or inhibitors. Among 9 potentially expressed endogenous X. laevis oocyte Leu transporter species, activities of only the uniporters SLC43A2/LAT4 (and/or SLC43A1/LAT3) and the sodium symporter SLC6A19/B0AT1 were required to account for total uptake. Furthermore, Leu and Phe uptake by heterologously expressed human SLC6A14/ATB0,+ and SLC43A2/LAT4 was accurately calculated. This versatile systems biology approach is useful for analyses where the kinetics of each active protein species can be represented by the Hill equation. Furthermore, its applicable even in the absence of protein expression data. It could potentially be applied, for example, to quantify drug transporter activities in target cells to improve specificity.

In Silico understanding of the cyclodextrin–phenanthrene hybrid assemblies in both aqueous medium and bacterial membranes

The explicit-solvent molecular dynamic (MD) simulation and adaptive biased forces (ABF) methods were employed to systemically study the structural and thermodynamic nature of the β-cyclodextrin (βCD) monomer, phenanthrene (Phe) monomer, and their inclusion complexes in both the aqueous and membrane environments, aiming at clarifying the atomic-level mechanisms underlying in the CD-enhanced degradation of polycyclic aromatic hydrocarbons (PAHs) by bacteria. Simulations showed that βCD and Phe monomers could associate together to construct two distinctive assemblies, i.e, βCD1–Phe1 and βCD2–Phe1, respectively. The membrane-involved equilibrium simulations and the data of potential of mean forces (PMFs) further confirmed that Phe monomer was capable of penetrating through the membranes without confronting any large energy barrier, whereas, the single βCD and βCD-involved assemblies were unable to pass across the membranes. These observations clearly suggested that βCD only served as the carrier to enhance the bioavailability of Phe rather than the co-substrate in the Phe biodegradation process. The Phe-separation PMF profiles indicated that the maximum of the Phe uptake by bacteria would be achieved by the “optimal” βCD:Phe molar ratio, which facilitated the maximal formation of βCD1–Phe1 inclusion and the minimal construction of βCD2–Phe1 complex.

Interaction of phenanthrene and potassium uptake by wheat roots: a mechanistic model

BackgroundPolycyclic aromatic hydrocarbons (PAHs) are potentially carcinogenic, mutagenic and toxic to both human and non-human organisms. Dietary intake of PAHs is a dominant route of exposure for the general population where food crops are a major source of dietary PAHs. Over 20% of main food crops contain PAHs that exceed the control limits in China. However, the mechanisms on PAH accumulation in crops are not well understood.ResultsHere we report the physiological mechanism of potassium (K+)-stimulated uptake of phenanthrene (PHE, a model PAH) in wheat. PHE uptake is stimulated by the external K+. The addition of blockers (tetraethlyammonium and barium) for K+ channels does not suppress the process, suggesting that K+ channels are not involved. The introduction of PHE and K+ elicits a much greater depolarization in root cell membrane potential than that of either PHE or K+. K+ activates the plasma membrane proton (H+)-ATPase in a K+-dependent manner. The pattern is quite similar to that in PHE uptake in the presence of K+. The external medium pH treated with PHE and K+ is higher than that with K+, and lower than that with PHE, indicating that H+ pump involves in the interaction between PHE and K+ uptake.ConclusionsTherefore, it is concluded that a K+ influx/H+ efflux reaction is coupled with the transport of PHE into wheat root cells. Our results provide a novel insight into the PHE uptake by crop roots.

Visibility of vascular phenylalanine in dynamic uptake studies in humans using magnetic resonance spectroscopy

In general, vascular contributions to the in vivo magnetic resonance (MR) brain spectrum are too small to be relevant. In cerebral uptake studies, however, vascular contributions may constitute a major confounder. MR visibility of vascular Phe was investigated by recording localized spectra from fully oxygenated and well-mixed whole blood. Blood Phe levels determined by MR spectroscopy (MRS) and ion-exchange chromatography showed excellent correlation. In addition, effects of blood flow were shown to have a small effect on signal amplitude with the MRS methodology used. Hence, blood Phe is almost completely MR visible at 1.5 T, even though it is severely broadened at higher fields. Without appropriate correction, cerebral Phe influx in studies of brain Phe uptake in phenylketonuria patients or healthy subjects would appear to be faster and lead to higher levels. Similar effects are envisaged for studies of ethanol or glucose uptake across the blood-brain barrier.

Preparation of phenylalanine imprinted polymer by the sol–gel transition method

A phenylalanine (Phe) imprinted polymer was prepared by the wet-phase inversion and sol–gel transition method to endow a copolymer matrix with a large uptake capacity of template molecules and prominent adsorption selectivity at the high concentration of the racemate solution. A copolymer bead prepared by wet-phase inversion was shrunken in a hydrochloric acid solution containing a large amount of template molecules after swelling in a sodium hydroxide solution. Template molecules were effectively implanted in the polymer matrix during shrinking after swelling. The adsorption selectivities of Phe-imprinted copolymer bead were 2.1 and 1.33 at 1 g and 10 g Phe/l racemate solution, respectively, and the Phe uptake capacity reached about 1 g Phe/g dry weight of the copolymer. The adsorption selectivity of the copolymer was retained after five batches of adsorption/desorption in 1 g Phe/l solution composed of 5% d-Phe and 95% l-Phe.

INCREASING THE ENERGY CONTENT OF MILK DOES NOT ALTER MUSCLE PROTEIN BALANCE FOLLOWING RESISTANCE EXERCISE

It has been shown that a potent stimulation of muscle protein metabolism in response to resistance exercise occurs after the ingestion of a combination glucose and a mixture of essential amino acids. Milk is an inexpensive and palatable alternative that both stimulates insulin and provides amino acids. However, the contribution of non-protein energy to muscle protein balance is unclear. PURPOSE This study was designed to examine the effect of a bolus ingestion of milk with different energy content on the response of muscle protein balance. METHODS Young, healthy, untrained subjects were randomly assigned to one of three groups: Control (CON), 237 ml fat-free milk (LO-E), or 237 ml whole milk (HI-E). Both milk groups contained the same amount of protein and carbohydrate, but lipids provided 1.75 times more energy for HI-E than LO-E. Study participants performed 10 sets of 8 repetitions of resistance leg exercise at 80% of one-repetition maximum (1RM), followed by drink ingestion one hour post-exercise. Femoral arterial and venous blood samples and leg blood flow measurements were taken to assess insulin levels and amino acid (phenylalanine [PHE]) concentration and consequent net protein balance across the leg for the duration of the 8-hour protocol. RESULTS Insulin levels were similar between LO-E and HI-E during the period following drink ingestion. Following drink ingestion, net PHE uptake was not different from zero during CON (−5±15 mg). Following milk ingestion, net PHE uptake was positive for both groups (32±9 and 36±20 mg for LO-E and HI-E, respectively). There was no difference in net PHE uptake between LO-E and HI-E groups. CONCLUSION These results support the hypothesis that the importance of non-protein energy to muscle protein balance is due to a stimulatory effect on insulin secretion other than the intake of energy, per se. Supported by Dairy Management Incorporated (DMI) and Shriners Hospital for Children 8490.

Insulin Stimulates Phenylalanine Uptake across the Hind Limb in Fed Lambs

Five lambs ( approximately 6 mo of age and 30 kg), with an external iliac artery and vein catheterized and fed to maintain body weight, were used to examine effects of close arterial infusion of insulin and branched-chain amino acids (BCAA) on net phenylalanine (Phe) uptake across the hind limb. Treatments, administered randomly on five consecutive days to each lamb, were 400 min infusions of: i) saline (control); ii) insulin to double iliac artery concentration (low insulin); iii) as ii but to quadruple insulin concentration (high insulin); iv) 30 micromol/min leucine and 22.5 micromol/min each isoleucine and valine (BCAA) and v) co-infusion of ii and iv. Blood was sampled over the last 200 min from the iliac vein and right ventricle of the heart. High insulin caused a slight decrease (-13%, P < 0.05) in systemic glucose concentration, but did not alter systemic insulin concentration. Insulin, at both doses and in combination with BCAA, resulted in 9-fold greater net Phe uptake (P < 0.05) than the control, as did BCAA alone. Because BCAA alone increased net Phe uptake, these may have stimulatory effects directly or may enhance endogenous insulin. Maximum stimulation was achieved with low insulin because there was no increase in net Phe uptake with high insulin or from co-infusion with BCAA. Insulin, at low concentrations, may be important to growth in animals with marginal nutrition.

Insulin stimulates phenylalanine uptake across the hind limb in fed lambs

Although insulin has been shown to stimulate muscle protein accretion in nonruminants (e.g., Wray-Cahen et al., 1998) evidence for this same effect in ruminants has been equivocal (e.g., Oddy et al., 1987; Wolff et al., 1989). Moreover, when insulin has been reported to have an anabolic effect in ruminants, the animal has been in the fasted state. In addition, Garlick and Grant (1988) have shown that branched-chain amino acids (BCAA) enhanced insulin-stimulated protein synthesis in fasted rats. The primary aim of the present study was to ascertain whether insulin increases phenylalanine (Phe) uptake (used as an index of skeletal muscle protein anabolism) across the hind limb of fed lambs. A secondary aim was to determine if infusion of BCAA, alone or in combination with insulin, would stimulate Phe uptake greater than insulin alone.

Uptake of labelled phenylalanine into different blood fractions in the portal vein and cranial mesenteric vein of lambs

SUMMARYFour lambs (mean 27 kg liveweight) offered 900 g/day lucerne chaff were prepared with catheters in the portal vein (PV), cranial mesenteric vein (CMV), femoral artery (FA) and abomasum. L-[2,6-3H]phenylalanine (Phe) and14C-(Phe)casein were infused into the abomasum in separate experiments. Concurrent samples of blood from the PV, CMV and FA were prepared as four fractions: plasma, deproteinized whole blood, free Phe in deproteinized whole blood, and whole blood. Ratios of net label uptakes in different blood fractions indicated that red blood cells and blood proteins were unlikely to contribute to net Phe uptake into the PV or CMV. Small peptides may have contributed up to 20% to total appearance of Phe in the PV and CMV. However, net uptake of peptides from the lumen was probably zero. It was concluded that the Phe uptake and, by implication, total amino acid uptake from the lumen of the small intestine into the PV and CMV were as free amino acids.

Competition for transport of amino acids into rat heart: Effect of competitors on protein synthesis and degradation

Transport of the neutral amino acids, 2-(methylamino)isobutyrate (MeAIB) and Phe, was examined in isolated rat hearts perfused by the Langendorff method. Hearts were perfused by recirculating for various time periods buffer containing [ 14C]-MeAIB or [ 14C]-Phe plus desired additions. Uptake of MeAIB was linear for approximately 30 minutes; Phe uptake was linear for a maximum of 5 minutes, and reached a steady state after 15 minutes. K m and V max for MeAIB were 1.1 ± 0.03 mmol/L and 37.7 ± 0.4 pmol/μL intracellular fluid (ICF)/min; values for Phe were 1.8 ± 0.02 mmol/L and 364 ± 5 pmol/μL ICF/minute. Uptake of MeAIB (0.2 mmol/L) was reduced 95% in the presence of Ser (10 mmol/L), and less severely by large neutral amino acids ([LNAA], 10 mmol/L) such as Phe and Leu (by 46% and 54%, respectively). Uptake of Phe (0.2 mmol/L) was reduced by LNAA such as Val, Leu, and Ile (by 51%, 78%, and 81%, respectively), or by commercial preparations used in parenteral nutrition, eg, Travasol or Travasol plus extra branched-chain amino acids (BCAA) (Branchamin); Ser had little effect (8% reduction). Insulin in the perfusion medium increased the fractional rate of protein synthesis. Individual BCAA at physiological concentrations (0.2 mmol/L) did not alter the rate of protein synthesis. Branchamin or Travasol plus Branchamin also had no effect on the rate of protein synthesis in heart, but did depress the rate of degradation. These studies suggest that amino acid transport into heart may be affected by normal levels of plasma amino acids, whereas protein synthesis is not.

Transport of a large neutral amino acid in a human intestinal epithelial cell line (Caco-2): uptake and efflux of phenylalanine

The processes of l-phenylalanine (Phe) uptake and efflux from the apical (AP) and basolateral (BL) sides of an intestinal epithelial cell line (Caco-2) were investigated to further characterize the mechanism of transcellular transport of this amino acid. The results indicated that the initial uptake rates of Phe were saturable with a K m of 2.7 nM for AP uptake and 0.18 mM for BL uptake. Unlike the uptake, the initial efflux rates were shown to be proportional to the intracellular concentrations of Phe. Based on these kinetic studies and determination of other characteristics (e.g., Na + dependency) of the uptake and efflux processes, it was concluded that AP uptake, BL uptake and BL efflux were distinctly different. This suggests that either different carriers or a different combination of carriers are responsible for the transmembrane transport of this amino acid. When the results of kinetic studies of Phe uptake and efflux were used to determine the rate-limiting step in the AP-to-BL transcellular transport of this amino acid, it was concluded that the BL efflux is the rate-limiting step in the transcellular transport of Phe in the Caco-2 cell monolayers.

Intestinal glycyl-L-phenylalanine and L-phenylalanine transport in a euryhaline teleost

The transport mechanisms for the dipeptide glycyl-L-phenylalanine (Gly-Phe) and L-phenylalanine (Phe) were characterized in fish intestinal brush-border membrane vesicles (BBMV). Gly-Phe was rapidly hydrolyzed only intravesicularly with almost total hydrolysis occurring even at 10 s. Dipeptide uptake was not stimulated by an inward gradient of Na, K, or H. Phe uptake was stimulated by an inward gradient of either Na or K but displayed an overshoot phenomenon only in the presence of an Na gradient. Kinetic analysis of the effect of substrate concentration on transport rate revealed that transport of both Gly-Phe and Phe occurred by a saturable process conforming to Michaelis-Menten kinetics. The Km for Gly-Phe was 9.8 +/- 3.5 mM, whereas that for Phe in the presence of Na or K, respectively, was 0.74 +/- 0.13 and 1.1 +/- 0.37 mM. Maximum uptake for Gly-Phe and for Phe in the presence of Na and K was 5.1, 0.9, and 0.4 nmol.mg and protein-1.5 s-1, respectively. Gly-Phe and Phe transport displayed different patterns of inhibition by dipeptides and amino acids. These results suggest that Gly-Phe and Phe are transported via different mechanisms, with Gly-Phe being hydrolyzed during a carrier-mediated, cation-independent process and Phe being transferred via a Na+ cotransport process similar to that described in mammals. During conditions of high luminal dipeptide concentrations, the Gly-Phe pathway may make a significant contribution to total Phe uptake.