Rate Of Leucine Uptake Research Articles

Surface productivity gradients govern changes in the viability of deep ocean prokaryotes across the tropical and subtropical Atlantic

AbstractProkaryotes represent a major fraction of marine biomass and play a key role in the global carbon cycle. We studied the vertical profiles (0–3500 m) of abundance, viability, and activity of prokaryotic communities along a productivity gradient in the subtropical and tropical Atlantic to assess whether there is a vertical linkage between surface productivity regimes and deep ocean prokaryotic communities. We found that latitudinal changes in the vertical patterns of cytometric variables were coupled with surface productivity: higher prokaryotic abundances and viabilities, and smaller cell sizes were observed below highly productive surface waters, an effect reaching down to the bathypelagic layer. Leucine uptake rates in deep waters showed no clear relationship with surface productivity. Changes in resource and energy allocation to growth vs. maintenance in hostile environments, cell‐size‐dependent metabolic requirements, and variability in leucine‐to‐carbon conversion may all be part of the array of factors involved in controlling the prokaryotic activity patterns that were measured. Our work adds to the recent findings that highlight the importance of vertical connectivity for prokaryotic communities in the dark ocean and unveils a remarkable impact of surface conditions in the viability of deep ocean prokaryotes. This is a key aspect when considering metabolic rates of prokaryotic communities in the bathypelagic realm.

Inorganic and organic carbon and nitrogen uptake strategies of picoplankton groups in the northwestern Atlantic Ocean

AbstractPicoplankton populations dominate the planktonic community in the surface oligotrophic ocean. Yet, their strategies in the acquisition and the partitioning of organic and inorganic sources of nitrogen (N) and carbon (C) are poorly described. Here, we measured at the single‐cell level the uptake of dissolved inorganic C (C‐fixation), C‐leucine, N‐leucine, nitrate (NO3−), ammonium (NH4+), and N‐urea in pigmented and nonpigmented picoplankton groups at six low‐N stations in the northwestern Atlantic Ocean. Our study highlights important differences in trophic strategies between Prochlorococcus, Synechococcus, photosynthetic pico‐eukaryotes, and nonpigmented prokaryotes. Nonpigmented prokaryotes were characterized by high leucine uptake rates, nonsignificant C‐fixation and relatively low NH4+, N‐urea, and NO3− uptake rates. Nonpigmented prokaryotes contributed to 7% ± 3%, 2% ± 2%, and 9% ± 5% of the NH4+, NO3−, and N‐urea community uptake, respectively. In contrast, pigmented groups displayed relatively high C‐fixation rates, NH4+ and N‐urea uptake rates, but lower leucine uptake rates than nonpigmented prokaryotes. Synechococcus and photosynthetic pico‐eukaryotes NO3− uptake rates were higher than Prochlorococcus ones. Pico‐sized pigmented groups accounted for a significant fraction of the community C‐fixation (63% ± 27%), NH4+ uptake (47% ± 27%), NO3− uptake (62% ± 49%), and N‐urea uptake (81% ± 35%). Interestingly, Prochlorococcus and photosynthetic pico‐eukaryotes showed a greater reliance on C‐ and N‐leucine than Synechococcus on average, suggesting a greater reliance on organic C and N sources. Taken together, our single‐cell results decipher the wide diversity of C and N trophic strategies between and within marine picoplankton groups, but a clear partitioning between pigmented and nonpigmented groups still remains.

Fine-scale variability in methanol uptake and oxidation: from the microlayer to 1000 m

Abstract. The aim of this research was to make the first depth profiles of the microbial assimilation of methanol carbon and its oxidation to carbon dioxide and use as an energy source from the microlayer to 1000 m. Some of the highest reported methanol oxidation rate constants of 0.5–0.6 d−1 were occasionally found in the microlayer and immediately underlying waters (10 cm depth), albeit these samples also showed the greatest heterogeneity compared to other depths down to 1000 m. Methanol uptake into the particulate phase was exceptionally low in microlayer samples, suggesting that any methanol utilised by microbes in this environment is for energy generation. The sea surface microlayer and 10 cm depth also showed a higher proportion of bacteria with a low DNA content, and bacterial leucine uptake rates in surface microlayer samples were either less than or the same as those in the underlying 10 cm layer. The average methanol oxidation and particulate rates were however statistically the same throughout the depths sampled, although the latter were highly variable in the near-surface 0.25–2 m compared to deeper depths. The statistically significant relationship demonstrated between uptake of methanol into particles and bacterial leucine incorporation suggests that many heterotrophic bacteria could be using methanol carbon for cellular growth. On average, methanol bacterial growth efficiency (BGEm) in the top 25 m of the water column is 6% and decreases with depth. Although, for microlayer and 10 cm-depth samples, BGEm is less than the near-surface 25–217 cm, possibly reflecting increased environmental UV stress resulting in increased maintenance costs, i.e. energy required for survival. We conclude that microbial methanol uptake rates, i.e. loss from seawater, are highly variable, particularly close to the seawater surface, which could significantly impact upon seawater concentrations and hence the air–sea flux.

Abstract 5148: Amino acid transporters ASCT2 and LAT1 ubiquitously function in N-myc (+) epithelial and mesenchymal human HCC cells exhibiting a wide array of mTOR and glycolytic reliance for growth

Abstract Amino acid transporters ASCT2 and LAT1 are coordinately enhanced in a broad array of human cancers where they associate in the plasma membrane and are proposed to work cooperatively to activate mTOR signaling through a tertiary-active transport mechanism involving glutamine (ASCT2) and essential branch-chain amino acids (LAT1). Silencing of ASCT2 expression in liver cancer cells has been shown to induce apoptosis and inhibit mTOR signaling while Myc expression has been implicated in promoting ASCT2 and LAT1 expression as well as a glutamine-intensive metabolic profile typical of many cancers, which helps support the switch to aerobic glycolysis (Warburg effect). In particular, ASCT2 and LAT1 are nearly undetectable in normal liver but are enhanced in hepatocellular carcinoma (HCC). To test the relationship between amino acid transporters, myc expression, metabolism and mTOR, we examined the expression and function of ASCT2 and LAT1 as a function of N-myc and C-myc status, reliance on glycolysis for growth and sensitivity to rapamycin (mTOR) in a broad panel of 14 human HCC lines (7 Group I (epithelial) and 7 Group II (mesenchymal)). We hypothesized that transporter expression is proportional to myc expression, and that glycolytic reliance and both transporters are enhanced in the more aggressive Group II HCC lines. Our results show that all human HCC lines are N-myc-, ASCT2- and LAT1-positive, and variably c-myc positive, with no clear correlation between specific myc isoform and transporter expression levels. In general, LAT1 protein expression was uniformly high in all mesenchymal HCC lines, but more variable in epithelial HCC, while BCH-inibitable leucine uptake rates displayed a wide array of values in both HCC groups; the same was true for ASCT2 protein and glutamine uptake activities. Treatment of HCC cells for 24 hours with ASCT2 and LAT1 substrate inhibitors GPNA and BCH, respectively, failed to inhibit mTOR signaling as indexed by 4EBP1 phosphorylation. Inhibition of glycolysis and growth with 3-bromopyruvate was generally more pronounced in epithelial HCC, but variably evident in both HCC groups. Rapamycin-dependent growth inhibition was variable between HCC lines and showed no preferential epithelial or mesenchymal HCC efficacy. Collectively, the results suggest that N-myc, ASCT2 and LAT1 are ubiquitously expressed in both epithelial and mesenchymal human HCC cells, where they help drive growth in cells variably reliant on mTOR signaling and glycolysis. Thus, both transporters remain the subject of ongoing investigation as targeted therapies for HCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5148. doi:1538-7445.AM2012-5148

Diel rhythmicity in amino acid uptake by Prochlorococcus

The marine cyanobacterium Prochlorococcus, the most abundant phototrophic organism on Earth, numerically dominates the phytoplankton in nitrogen (N)-depleted oceanic gyres. Alongside inorganic N sources such as nitrite and ammonium, natural populations of this genus also acquire organic N, specifically amino acids. Here, we investigated using isotopic tracer and flow cytometric cell sorting techniques whether amino acid uptake by Prochlorococcus is subject to a diel rhythmicity, and if so, whether this was linked to a specific cell cycle stage. We observed, in contrast to diurnally similar methionine uptake rates by Synechococcus cells, obvious diurnal rhythms in methionine uptake by Prochlorococcus cells in the tropical Atlantic. These rhythms were confirmed using reproducible cyclostat experiments with a light-synchronized axenic Prochlorococcus (PCC9511 strain) culture and (35)S-methionine and (3)H-leucine tracers. Cells acquired the tracers at lower rates around dawn and higher rates around dusk despite >10(4) times higher concentration of ammonium in the medium, presumably because amino acids can be directly incorporated into protein. Leucine uptake rates by cells in the S+G(2) cell cycle stage were consistently 2.2 times higher than those of cells at the G(1) stage. Furthermore, S+G(2) cells upregulated amino acid uptake 3.5 times from dawn to dusk to boost protein synthesis prior to cell division. Because Prochlorococcus populations can account from 13% at midday to 42% at dusk of total microbial uptake of methionine and probably of other amino acids in N-depleted oceanic waters, this genus exerts diurnally variable, strong competitive pressure on other bacterioplankton populations.

Effects of resource availability and bacterivory on leucine incorporation in different groups of freshwater bacterioplankton, assessed using microautoradiography

We examined changes in the phylogenetic structure and leucine incorporation of bacte- rioplankton assemblages exposed to variable levels of available resources and bacterivory in a fresh- water reservoir. Fluorescence in situ hybridization (FISH) combined with microautoradiography was used to determine bacterial phylogenetic affiliations and the proportions of cells incorporating leucine. Grazing-free and grazing-enhanced treatments were incubated in both P-limited and P-rich areas of the reservoir using dialysis bags, and bottle treatments with and without P enrichment. β-Proteobacteria, mainly the R-BT065 cluster (subcluster of Rhodoferax sp. BAL47), became the dominant leucine-active bacteria in all treatments. Proportions of active cells belonging to R-BT065 phylotypes considerably increased under conditions of enhanced protistan grazing and phosphorus availability. In contrast, proportions of cells from the Sphingobacteria/Flavobacteria group usually decreased and exhibited very low rates of leucine uptake. γ-Proteobacteria was the least abundant but nevertheless a highly active part of the assemblage. Phosphorus addition supported incorporation of leucine by all bacterial groups. Although highly vulnerable to predation, only R-BT065 cells exhib- ited marked increases in both relative abundance within the bacterial community and in proportions of active cells. The phylogenetic composition and leucine-uptake of bacterioplankton was more markedly affected by resource availability than by grazing pressure, which only had a strong effect on the dynamics of R-BT065 bacteria within the P-limited area of the reservoir.

Dietary protein reduction in sheep and goats: different effects on L-alanine and L-leucine transport across the brush-border membrane of jejunal enterocytes.

It was the aim of this study to examine the potential regulatory effects of a long-term low dietary protein supply on the transport capacity of the jejunal brush-border membrane for amino acids. For this purpose, we used the neutral amino acids L-alanine (representative for nonessential amino acids) and L-leucine (representative for essential amino acids) as model substances. Ten sheep lambs, 8 weeks of age and 19-27 kg body weight, were allotted to two dietary regimes with either adequate or reduced protein supply which was achieved by 17.9% and 9.7% of crude protein in the concentrated feed, respectively. The feeding periods were 4-6 weeks in length. Similarly, eight goat kids of 5-7 weeks of age and 8-14 kg body weight were allotted to either adequate (crude protein 20.1%, feeding period 9-12 weeks) or reduced protein supply (10.1%, feeding period 17-18 weeks). Dietary protein reduction in lambs caused a significant body weight loss of 0.6 +/- 0.7 kg, whereas the body weight in control animals increased by 1.9 +/- 0.7 kg (P<0.05). Plasma urea concentrations decreased significantly by 60% (low protein 2.3 +/- 0.1 versus control 5.7 +/- 0.2 mmol l(-1), P<0.001). In kids, reduction of dietary protein intake led to significant decreases of the daily weight gain by 48% from 181 +/- 8 g to 94 +/- 3 g (P<0.001) and daily dry matter intake by 27% from 568 +/- 13 g to 417 +/- 6 g (P<0.01). Respective urea concentrations in plasma were reduced by 77% from 5.2 +/- 0.4 to 1.2 +/- 0.2 mmol l(-1) (P<0.01). Kinetic analyses of the initial rates of alanine uptake into isolated jejunal brush-border membrane vesicles from sheep and goats as affected by low dietary protein supply yielded that the apparent Km was neither significantly different between the species nor significantly affected by the feeding regime thus ranging between 0.12 and 0.16 mmol.l(-1). Reduction of dietary protein, however, resulted in significantly decreased Vmax values of the transport system by 25-30%, irrespective of the species. Kinetic analyses of the initial rates of leucine uptake into jejunal brush-border membrane vesicles from sheep and goats yielded that leucine uptake was mediated by Na+-dependent as well as Na+-independent processes. Similar to alanine, apparent Km values of leucine uptake were neither different between the species nor affected due to low dietary protein and ranged between 0.08 and 0.15 mmol l(-1). In contrast to the alanine transport mechanism, dietary protein reduction resulted in increased Vmax values of Na+-dependent leucine transport by 53% in sheep and 230% in goats. Similarly, Na+-independent leucine uptake was stimulated by 85% and 200% in sheep and in goats, respectively. This study shows adaptation of amino acid absorption at the brush-border membrane level of jejunal enterocytes of small ruminants due to dietary protein reduction. Whereas the transport capacity for the nonessential amino acid alanine was reduced due to low dietary protein, the transport capacity for the essential amino acid leucine was markedly stimulated. From this, the involvement of rather different feedback mechanisms in adaptation of intestinal amino acid transport mechanisms has to be discussed.

A novel regulatory mechanism for amino acid absorption in lepidopteran larval midgut

A number of methyl and ethyl esters of naturally occurring amino acids exert a potent stimulatory effect on the cotransport system responsible for the absorption of most essential amino acids along the midgut of the silkworm Bombyx mori. l-Leucine methyl ester (Leu–OMe), one of the most effective activators, induces a large increase of the initial rate of leucine uptake in midgut brush border membrane vesicles (BBMV) from the anterior–middle (AM) region, and a small effect in BBMV from the posterior (P) region. Nonetheless, the methyl ester causes in both regions a relevant K +-, Δ ψ- and pH-independent increase of the intravesicular accumulation of the amino acid. The activation by Leu–OMe proves that amino acid absorption can be modulated all along the B. mori larval midgut and that the AM region, where the ability to transport and concentrate the substrate is very low, is more susceptible than the P region. Leucine uptake in AM-BMMV can be activated by amino acid methyl esters with definite structural requisites, with the following order of potency: l-leucine> l-phenylglycine> l-methionine> l-phenylalanine> l-norleucine≫ l-isoleucine. The activation is stereospecific and occurs also with some ethyl esters (e.g. leucine and phenylalanine). No activation was observed with esters of amino acids with short hydrophobic or polar side-chains. The activation mechanism here described plays a fundamental role in larval growth since silkworms reared on artificial diets supplemented with leucine or methionine methyl esters reach maximum body weight 12–18 h before control larvae and spin cocoons with a larger shell weight. This novel regulatory mechanism of an amino acid transport protein appears to be widespread among lepidopteran larvae.

An Isotope Dilution Model for Partitioning Leucine Uptake by the Liver of the Lactating Dairy Cow

An isotope dilution model for partitioning leucine uptake by the liver of the lactating dairy cow is constructed and solved in the steady state. If assumptions ae made, model solution permits calculation of the rate of leucine uptake from portal and hepatic arterial blood supply, leucine export into the hepatic vein, leucine oxidation and transamination, and synthesis and degradation of hepatic constitutive and export proteins. The model requires the measurement of plasma flow rate through the liver in combination with leucine concentrations and plateau isotopic enrichments in arterial, portal and hepatic plasma during a constant infusion of [1-13C]leucine tracer. The model can be applied to other amino acids with similar metabolic fates and will provide a means for assessing the impact of hepatic metabolism on amino acid availability to peripheral tissues. This is of particular importance when considering the dairy cow and the requirements of the mammary gland for milk protein synthesis.

Uptake of free amino acids by the ophiuroid Microphiopholis gracillima (Stimpson) (Echinodermata) during disc regeneration

1. 1. Intact and regenerating brittlestars ( Microphiopholis gracillima) take up several amino acids from artificial seawater, and show significant increases in uptake with food deprivation. 2. 2. There were no differences in total amino acid uptake rates (determined by high performance liquid chromatography) between intact and regenerating animals. 3. 3. No increases in the gross rate of leucine uptake were apparent in either group over time; however, glycine uptake increased significantly. 4. 4. Catabolism of leucine and glycine, as evidenced by labeled CO 2 release, was highest among intact animals that had been held for several days. 5. 5. Dissolved leucine appears to be rapidly catabolized, while glycine tends to remain in tissues.

Increased mass transfer to microorganisms with fluid motion

The effect of fluid flow and laminar shear on bacterial uptake was examined under conditions representative of the fluid environment of unattached and attached cells in wastewater treatment bioreactors. Laminar shear rates below 50 s(-1) did not increase leucine uptake by suspended cultures of Zoogloea ramigera. However, leucine uptake by cells fixed in a flow field of approximately 1 mm s(-1) was 55-65% greater than uptake by suspended cells. Enhanced microbial uptake with advective motion is consistent with mass transfer rates calculated using Sherwood number correlations. Advective flow increases microbial uptake by increasing collisions between substrate molecules and cells through compression of the concentration boundary layer surrounding a cell. The rate of leucine uptake suggests that binding proteins used to transport leucine into the cell can occupy approximately 1% of the cell surface area.

Transport of L‐leucine in the fission yeast Schizosaccharomyces pombe

AbstractTransport of L‐leucine into Schizosaccharomyces pombe cells from the stationary phase of growth (after preincubation for 60 min with 1% glucose) proceeds uphill, practically unidirectionally, and is mediated by at least two systems: a high‐affinity system with a KT of 0·045 mmol 1−1 and Jmax of 3·3 nmol min−1 (mg dry weight)−1 and a low‐affinity system with a KT of 1·25 mmol 1−1 and Jmax of 16·0 nmol min−1 (mg dry weight)−1. The high‐affinity system has a pH optimum at 3.2, the accumulation ratio is highest at a cell density of 2–4 mg dry weight per ml and decreases with increasing leucine concentration. Transport of leucine by the high‐affinity system is strongly inhibited by proton conductors, ammonium ions and by most amino acids, but only L‐phenylalanine, L‐isoleucine, L‐valine and L‐cysteine behave as fully competitive inhibitors. Systems of L‐leucine transport in S. pombe are not constitutive. Transport activity appears only after preincubation of cells with a suitable source of energy. If cycloheximide is added during preincubation with glucose, no transport systems for leucine are synthesized. After removal of glucose, the activity of transport systems decays with a half‐time of about 20 min. The presence of cyclic AMP increases the initial rate of leucine uptake only in cells preincubated with glucose and in the absence of cycloheximide.

Leucine uptake and protein synthesis are exponential during the division cycle of Escherichia coli B/r.

The rate of leucine uptake, which is a measure of protein synthesis, was measured during the division cycle of Escherichia coli B/r by the membrane elution technique. The rate of leucine uptake was exponential, indicating that protein synthesis is exponential, and not linear, during the division cycle. These results, coupled with the results of other work on the exponential rate of RNA synthesis during the division cycle, indicate that the accumulation of mass in E. coli and other gram-negative organisms is exponential during the division cycle.

A novel sodium-dependent uptake system for l-leucine in rat brain synaptosomes

A novel Na(+)-dependent system for the uptake of l-leucine by rat brain synaptosomes is described. At a constant osmolarity of 270 mOsm/L, it functions optimally at a Na(+) concentration of 10 mM. This system is determined by measuring the difference in leucine uptake in the presence and absence of Na(+) as well as by measuring the residual uptake of leucine in the presence of an excess amount of 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid in a Na(+) -containing medium. Mg(2+) is found to enhance leucine uptake in the presence and absence of Na(+). However, its presence in the incubation medium reduces net leucine uptake rates due to Na(+) and also alters K(m) and V(max) values for the Na(+) -dependent uptake system.

Leucine transport in relation to the activities of Na+-H+ antiporter and Na+/K+ pump stimulated by serum and a tumor promoter.

Fetal calf serum and 12-O-tetradecanoylphorbol 13-acetate (TPA) increased the rate of leucine uptake by Chang liver cells in Na+-containing medium. Addition of monensin to the incubation medium also increased the leucine uptake. All these agents were capable of raising the cytoplasmic pH, which was blocked by a prior addition of amiloride or removing Na+ from assay medium, suggesting activation of Na+-H+ exchange across the cell membrane by fetal calf serum and TPA. The stimulation of leucine uptake by monensin and fetal calf serum was blocked completely or incompletely by addition of ouabain or amiloride. The basal and fetal-calf-serum- or TPA-stimulated leucine uptake was extensively depressed by the presence of an excess of 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid in the incubation medium. Based on these results it is proposed that the transport of leucine by the system L is stimulated by fetal calf serum and TPA with a high concentration of Na+ outside the cells as a result of alkalinization of the cytoplasm and coordinated activation of (Na+ + K+)-ATPase by these stimulators to maintain the transmembrane Na+ gradient and also hyperpolarize the cell membrane.

Leucine transport in relation to the activities of [formula omitted] antiporter and Na +/K + pump stimulated by serum and a tumor promoter

Fetal calf serum and 12-O- tetradecanoylphorbol 13- acetate (TPA) increased the rate of leucine uptake by Chang liver cells in Na +-containing medium. Addition of monensin to the incubation medium also increased the leucine uptake. All these agents were capable of raising the cytoplasmic pH, which was blocked by a prior addition of amiloride or removing Na + from assay medium, suggesting activation of Na +− H + exchange across the cell membrane by fetal calf serum and TPA. The stimulation of leucine uptake by monensin and fetal calf serum was blocked completely or incompletely by addition of ouabain or amiloride. The basal and fetal-calf-serum- or TPA-stimulated leucine uptake was extensively depressed by the presence of an excess of 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid in the incubation medium. Based on these results it is proposed that the transport of leucine by the system L is stimulated by fetal calf serum and TPA with a high concentration of Na + outside the cells as a result of alkalinization of the cytoplasm and coordinated activation of ( Na + + K +)- ATPase by these stimulators to maintain the transmembrane Na + gradient and also hyperpolarize the cell membrane.

Schistosoma mansoni: Effect of maintenance in vitro on the uptake and incorporation of leucine by adult worms

The rates of leucine uptake and incorporation into protein by adult male and female Schistosoma mansoni were not affected by maintenance in vitro for up to 10 days' duration, despite the decline in the protein content of male and female worms of approximately 35 and 55%, respectively, during this period. The effect of maintenance in vitro was obscured in paired female schistosomes by the apparent shielding of the female tegument within the gynaecophoral canal of the male. Incorporation rates were reduced by 50% in the presence of 2 mM cycloheximide whereas uptake rates were unaffected. Adult schistosomes are unable to maintain their in vivo protein levels purely by recourse to exogenous amino acids absorbed across the tegument in vitro, and the rates of uptake and incorporation of leucine appear to reflect the changing somatic requirements of the worms and are probably not correlated with the reproductive activity of adult worms in vitro. The possible role of alimentary rather than tegumental nutrition in egg production in vivo is discussed.

Autoradiographic analysis of amino acid uptake by the gill ofMytilus

Autoradiography was used to examine the influence of lateral ciliary activity on the pattern of leucine uptake into isolated gill tissue from the mussel,Mytilus californianus. Metachronal activity of the lateral cilia, normally absent in the in vitro gill, was reestablished by application of 10 μM 5-hydroxytryptamine (5-HT). This treatment produced a 5–7 fold stimulation in the rate of leucine uptake into isolated gills. The treatment with 5-HT did not, however, affect the fractional incorporation of leucine into alcohol insoluble vs alcohol soluble material. Autoradiograms of gills treated with 5-HT showed extensive labelling of frontal, lateral, and abfrontal surfaces of gill filaments compared to the control condition in which label was largely confined to the frontal region of the gill. Quantitative analyses of the autoradiograms revealed a 4-fold increase in the number of silver grains over lateral and abfrontal surfaces compared to control gills. Autoradiograms of gills from intact mussels exposed to3H-leucine showed a pattern of silver grain deposition similar to that observed in in vitro gills treated with 5-HT. It is concluded that the capacity for amino acid transport exists in cells from the frontal, lateral, and abfrontal surfaces of gill filaments, butaccess to dissolved substrates by transport sites on lateral and abfrontal surfaces is dependent upon lateral ciliary activity.

Regulation of Development of Leucine Uptake Activity by Glutamine in the Scutellum of Germinating Barley Grain

Scutella from ungerminated grains of barley (Hordeum vulgare L. cv Pirkka) take up leucine at a slow rate, which increases rapidly during germination. When endosperms were removed from the grains after imbibition for 4 hours or after germination for 12 or 72 hours, the increase in the rate of leucine uptake was greatly accelerated during subsequent incubation of the embryos or scutella. These increases were rapidly inhibited by cordycepin and cycloheximide, suggesting that protein synthesis, probably synthesis of the carrier protein, was required for the development of the uptake activity.In separated embryos or scutella, the increases in the leucine uptake activity were inhibited by glutamine. The inhibitions caused by glutamine and cycloheximide were not additive, suggesting that glutamine did not interfere with the function of the carrier but repressed its synthesis. Glutamine did not inhibit the simultaneous increase in peptide uptake; in this respect, its effect was specific for leucine uptake, which appears to be due to a general amino acid uptake system.Some other protein amino acids also inhibited the increase in leucine uptake without inhibiting the increase in peptide uptake. However, these effects were smaller than that of glutamine.These results suggest that the transfer of leucine (and other amino acids) from the endosperm to the seedling in a germinating barley grain is regulated at the uptake step by repression of the synthesis of the amino acid carrier protein by glutamine and-possibly to a lesser extent-by some other amino acids taken up from the endosperm.

Selective breeding of chickens for erythrocytes with high and low leucine transport activity.

Two lines of chickens, one high and the other low uptake, have been selected for three generations for their ability to transport leucine into erythrocytes. Significant line differences were produced in one generation of selection with further separation resulting in later generations. Selection progress has been exclusively with the high-uptake line, the low line not differing significantly from the control. The maximal rate of leucine uptake, the stimulation of leucine transport by medium Na+, lysine uptake, and the Na+-K+-ATPase activity all were greater in the high line. Rates of glucose transport were not different between the lines nor were intracellular concentrations of Na+ or K+.