Stimulation of renal amino acid reabsorption after treatment with triiodothyronine or dexamethasone in amino acid loaded rats

Summary In adult female anaestetized rats, the influence of triiodothyronine or dexamethasone on renal amino acid handling was investigated in leucine (20mg/100g b.wt.) or glutamine (45mg/100g b.wt.) loaded animals. Bolus injections of both amino acids were followed by temporary increase in fractional excretion of the administered amino acids as well of the endogenous amino acids which were not administered.Under load conditions (leucine and glutamine), dexamethasone treatment (60 g/100 g b.wt. for 3 days, i.p. once daily) was followed by a stimulation of renal amino acid reabsorption. The increase in fractional amino acid excretion after amino acid load was significantly lower than in untreated rats. The effect of triiodothyronine (20,g/1008 b.wt. for 3 days, i.p. once daily) was different in leucine and glutamine loaded animals: after leucine bolus injection a comparable stimulatory effect as shown for dexamethasone could be demonstrated, but after glutamine administration the stimulatory action of T3 was masked. T3 even increases fractional amino acid excretion in glutamine loaded rats as a sign of enhanced house-keeping in the renal tubular cells. These results confirm previous findings and indicate different effects of both hormones on the renal handling of amino acids.     

Influence of triiodothyronine and dexamethasone on renal amino acid handling in rats loaded with various amino acid mixtures

Summary In adult female rats, the influence of dexamethasone or triiodothyronine on renal amino acid handling was investigated in amino acid loaded animals. Amino acids were administered intravenously as two mixtures, each containing four amino acids to overload amino acid reabsorption capacity. Bolus injections of both mixtures were followed by temporary increase in fractional excretion of the administered amino acids as well of the amino acids which were not covered in the mixtures. The administration of the two mixtures was followed by different interactions between various amino acid carriers.After dexamethasone pretreatment (60µg/100g b.wt. for 3 days, once daily) a stimulation of the renal amino acid handling could be shown. Triiodothyronine (20µg/100g b.wt. for 3 days, once daily) did not increase tubular reabsorption capacity for amino acids. It even increased fractional amino acid excretion in amino acid loaded rats as a sign of enhanced amino acid metabolism in the kidney and/or increased amino acid uptake into the tubular cells from the luminal site.     

Renal handling of amino acids in 5/6-nephrectomized rats: Stimulation of renal amino acid reabsorption after treatment with triiodothyronine or dexamethasone under amino acid load

Summary In anaesthetized adult female rats, the renal amino acid handling was measured six days after 5/6 nephrectomy (5/6NX). The distinct rise in blood urea nitrogen as well as the significant reduction in urine flow and GFR indicate an impairment of kidney function. In principle, in 5/6NX rats amino acid plasma concentrations were comparable to those of control animals with two intact kidneys, whereas the fractional excretions (FE_AA) of most endogenous amino acids measured were significantly enhanced. After bolus injection of leucine or taurine (each 20 mg/100 g b.wt.) or glutamine (90 mg/ 100 g b.wt.), dissolved in 2m1 normal saline per 100 g b.wt., the FE_AA of both the amino acids administered and the endogenous amino acids increased as a sign of overloaded amino acid reabsorption capacity. This effect was more pronounced in 5/6NX rats than in controls. As early as one hour after amino acid load, plasma concentrations and FE_AA returned to baseline values of 5/6NX rats. A pretreatment with triiodothyronine (20,µg/100 g b.wt.) or dexamethasone (60 µg/100 g b.wt.), both given intraperitoneally once daily for 3 days, stimulated the renal amino acid transport capacity in 5/6NX rats: the increase in FE_AA after amino acid load was significantly lower compared to non-pretreatred animals. This stimulation could be shown for the bolus amino acids and the endogenous amino acids and was more distinct in 5/6NX rats than in controls with two intact kidneys.     

Renal amino acid transport in immature and adult rats during chromate and cisplatinum-induced nephrotoxicity

Summary. The effects of sodium dichromate (chromate; 1 mg/100 g b. wt. s.c.) and cisdiamminedichloroplatinum(II) (CP; 0.6 mg/100 g b. wt. i.p.) on renal amino acid excretion and plasma amino acid composition were investigated in 10- and 55-day-old anaesthetised rats. On the basis of diuresis experiments on conscious rats the mentioned doses and times (1^st day after chromate in both age groups and in 10-day-old rats after CP and 3^rd day after CP in adult rats) were found out to be optimal for the characterisation of amino acid transport after heavy metal poisoning. Interestingly, in conscious 10-day-old rats chromate nephrotoxicity is not detectable after 1 mg/100 g b. wt. whereas all of the other experimental groups showed nephrotoxic effects of chromate and CP in conscious rats. Urine volumes are lower, but not significantly, in anaesthetised immature rats, independently of the administered nephrotoxin. But GFR is significantly lower in 10-day-old rats, both in controls and after CP, whereas after chromate GFR is significantly reduced only in adult rats and age differences disappeared. In principle the renal fractional excretion (FE) of amino acids was distinctly higher in immature rats as a sign of lower amino acid reabsorption capacity. Nevertheless, the amino acid plasma concentrations were relatively high in immature rats. However, both chromate and CP did not distinctly influence amino acid plasma concentrations. But in both age groups the administration of chromate and CP significantly decreased amino acid reabsorption capacity (increase in FE) as a sign of nephrotoxicity, most pronounced in adult rats after CP. The investigation of renal amino acid handling confirms (1) that both CP and chromate are nephrotoxins, (2) that CP was more nephrotoxic in 55-day-old animals compared to immature rats as could be demonstrated before using other parameters for nephrotoxicity testing and showed (3) that determination of renal amino acid handling is a highly sensitive marker for nephrotoxicity testing, especially in immature rats. Received March 3, 2000 Accepted October 11, 2000     

Influence of an extracellular volume expansion (ECVE) on renal amino acid- and sodium handling in patients with autosomal dominant polycystic kidney disease (ADPKD)

Summary Although ADPKD is one of the first kidney diseases to be understood from the gene to the pathogenesis of clinical abnormalities, there were no data concerning the renal handling of amino acids and possible disorders of amino acid (AA) pattern in these patients. Therefore, in 9 patients suffering from ADPKD and in 8 healthy normal persons (NP) renal amino acid excretion was measured before and after extracellular volume expansion (ECVE) (21 of physiological electrolyte solution). Renal function was stable in both groups (serum creatinine: ADPKD: 85.1 ± 18.4 vs. NP 84.4 ± 13.5 mol/l; GFR: 93.8 ± 16.4 vs. 104.4 ± 9.4 ml/min/1.73 m²). Mean blood pressure was higher in ADPKD patients than in NP (99.4 ± 2.6 vs. 85.5 ± 2.4 mmHg), but did not change after ECVE. After ECVE in both groups, urine volume increased distinctly, whereas GFR was only slightly enhanced. The plasma concentrations of leucine, glycine, valine, threonine, glutamine, and alanine were significantly higher in controls than in ADPKD patients. The amino acid reabsorption capacity was reduced in ADPKD patients in 12 of 21 amino acids before ECVE. After ECVE, the fractional excretion of amino acids (FE_AA) increased only in NP. In parallel with changes in amino acid handling, the FE_Na (%) after ECVE increased both in ADPKD patients and in NP (before ECVE - ADPKD: 1.22 ± 0.23 vs. NP: 1.53 ± 0.23; after ECVE: 3.17 ± 0.25 (ADPKD) vs. 2.74 ± 0.22/NP; (ADPKD p 0.01, NP p 0.02) whereas FE_Li (%) increased significantly only in ADPKD (p 0.045) range (before ECVE - ADPKD: 25.8 ± 8.9 vs. NP: 20.5 ± 4.0; after ECVE: 41.4 ±15.4 vs. 25.2 ± 3.9). Furthermore, concentrations of cGMP (pmol/ml) in plasma increased after ECVE (before ECVE - ADPKD: 5.31 ± 0.56 vs. NP: 6.65 ±0.79; after ECVE: 11.31 ± 1.66 vs. 11.30 ± 1.91; p 0.05). Na⁺-dependent and, perhaps, NO-mediated processes in the reabsorption of AA in the proximal tubule seem to be different in ADPKD and may be related to different distributions of receptors and ATP-dependent transport systems with pathogenetic impact on abnormal transtubular fluid transport in ADPKD.     

Inhibition of kidney function after blockade of thromboxane synthetase by imidazole in anaesthetized rats

Experiments on anaesthetized female Wistar rats have shown that imidazole reduces renal excretion of p-aminohippurate (PAH). This effect occurs only after administration of imidazole simultaneously with a volume load (2 ml/100 g b.wt.). Injection of imidazole immediately before a PAH bolus (100 mg/100 g b.wt. in 2 ml) is followed by reduced PAH excretion via urine for at least 1 hour. In contrast, if a PAH bolus is given 20 min or later after imidazole no effect of this drug on renal PAH transport is demonstrable. These findings indicate that imidazole can interfere effectively with thromboxane synthesis only if thromboxane production is activated by volume expansion. Interestingly, despite 40% reduction of renal PAH excretion in volumen loaded rats, PAH serum disappearance is identical in controls and imidazole treated rats. Thus differences in the volume of distribution for PAH after imidazole must be expected. Under our experimental conditions imidazole was without effect on renal electrolyte excretion.     

Effect of aldosterone on incorporation of amino acids into renal medullary proteins

Summary Studies on the effects of pretreatment with aldosterone on the incorporation of³H leucine or³H methionine into proteins in renal slices were carried out in Joklik-modified minimal essential medium. Administration of aldosterone (2 g/100 g body wt) to adrenalectomized rats increased³H leucine incorporation into trichloroacetic acid insoluble fractions of crude homogenates of cortical slices by 15.5±0.4% and of medullary slices by 53.5±1.3%. No increase in isotope incorporation was observed in slices of renal papilla or spleen prepared from the same rats. Aldosterone had no effect on the³H-leucine content of the trichloroacetic acid-soluble fractions of all three renal zones and the spleen. The dose of aldosterone that elicited a half-maximal increase in³H-methionine incorporation into proteins of renal medullary slices (0.45 g of aldosterone/100 g body wt) was indistinguishable from that needed to elicit a halfmaximal increase in the urinary K⁺/Na⁺ ratio (0.35 g of aldosterone/100 g body wt). Dexamethasone, a potent glucocorticoid, at a dose of 0.8 g/100 g body wt did not augment³H-leucine incorporation into renal medullary proteins but was effective at 8 g/100 g body wt. Spirolactone (SC-26304), a potent anti-mineralocorticoid, abolished the effect of aldosterone on amino acid incorporation into medullary proteins when administered at a 100-fold higher dosage [i.e., 80 gvs. 0.8 g (per 100 g body wt)]. These results imply that the action of aldosterone on amino acid incorporation is mediated by the mineralocorticoid rather than the glucocorticoid pathway, presumably the mineralocorticoid receptors. Moreover, pretreatment of the rats with actinomycin D (70–80 g/100 g body wt) erased the effect of aldosterone (0.8 g/100 g body wt) on amino acid incorporation into medullary proteins.In paired experiments with³H and³⁵S methionine, aldosterone (0.8 g/100 g body wt) increased methionine incorporation into trichloroacetic acid precipitable proteins of subcellular fractions of the renal medulla. The effect of aldosterone on incorporation of methionine into medullary cytosol proteins was analyzed further by polyacrylamide gel electrophoresis at pH 8.3 in tris-glycine buffer. The gel profiles indicate that aldosterone significantly increased methionine incorporation into at least one protein (independent of the isotope) with a molecular weight of 31,000. This increase was inhibited by either pretreatment of the rat with actinomycin D (70–80 g/100 g body wt or SC-26304 (80 g/100 g body wt). Dexamethasone (0.8 g/100 g body wt) did not increase incorporation of methionine into the medullary cytosol proteins resolved by polyacrylamide gel electrophoresis.     

Branched chain amino acid aminotransferase isoenzymes of Pseudomonas cepacia

Pseudomonas cepacia grew rapidly using a mixture of all three branched chain amino acids as carbon source, but failed to use individual branched chain amino acids as sole carbon source. Extracts of bacteria grown on branched chain amino acids had between 2- and 3-fold higher levels of -ketoglutarate-dependent branched chain amino acid aminotransferase activity than extracts of glucose-grown bacteria. The increase in enzyme activity was due to the presence of a second aminotransferase not detected in extracts of glucose-grown bacteria. The enzyme, which presumably plays a role in branched chain amino acid degradation, had an apparent molecular weight (mol. wt.) of 75,000. The other aminotransferase was formed constitutively and apparently functions in synthesis of branched chain amino acids. It was more stable than the 75,000 mol.wt. enzyme, and was purified to homogeneity and found to be a 180,000 mol.wt. oligomer containing 6 subunits of approximately 30,000 mol.wt. Antiserum prepared against the purified enzyme inhibited its activity but failed to influence the activity of the 75,000 mol.wt. aminotransferase, suggesting that the two isoenzymes are encoded by different genes.     

Differential coupling efficiency of chemically activated amino acid to tRNA

Summary Interaction based on possible chemical affinity of an amino acid for tRNA was examined as a model for the aminoacylation of primitive tRNA without aid of an enzyme system. Two types of reaction were carried out and compared. One was the acyl linkage of amino acid to the 5-terminal phosphate of a tRNA activated as an imidazolide. The other was the incorporation of an amino acid activated as an imidazolide into 2(3)-hydroxyl groups of intact tRNA. Both types of reaction indicated that none of the amino acids tested had any selectivity for the tRNAs examined. However, the rates of reaction with a given tRNA were different among amino acids. In the second type of reaction, amino acids were found mainly at loop-out regions of tRNA, but not at either its 5- or 3-terminal sitesOneA ₂₆₀ unit is defined as an amount of material which gives an absorption of 1.0 at 260 nm when dissolved in 1 ml water and measured with a 1-cm light path     

黑水虻幼虫氨基酸及其微量元素分析

黑水虻具有较高的营养价值,是一种重要的环境友好型资源昆虫.本研究采用凯氏定氮法、茚三酮柱后衍生离子交换色谱法和微波消解-电感耦合等离子质谱法(ICP-MS)等多种分析技术,测定了厨余垃圾饲喂的黑水虻幼虫蛋白质、氨基酸和微量元素的组成及含量.研究结果表明,黑水虻幼虫中蛋白质的含量为40.60 g/100 g.在测定的16...     

Analysis of trace amino acid neurotransmitters in hypothalamus of rats after exhausting exercise using microdialysis

A simple but effective coupling of microdialysis and capillary electrophoresis with laser induced fluorescence detection technique was applied to analysis of amino acid neurotransmitters in the hypothalamus of rats after acute exhausting exercise. The separation of amino acids was achieved using an uncoated fused-silica capillary (57 cm×75 μm I.D.) with a buffer of 10 mM disodium tetraborate at pH 10 and an applied voltage of 12.5 kV. The detection limit was 10⁻¹⁰ M for each amino acid. It is sufficiently sensitive and rapid for the determination of amino acids in a 5-μl Microdialysate. In comparison to pre-exercise, a significant increase in the levels of six hypothalamic amino acids (arginine, glycine, lysine, glutamic acid, alanine, γ-amino-n-butyric acid) was found after exercise. These results demonstrate that the increase of metabolic amino acids in the hypothalamus of rats can be induced by exhausting exercise and suggests that amino acid neurotransmitters may play functional roles in the central effects of exercise.     

Amino acid transport system y+L of human erythrocytes: Specificity and cation dependence of the translocation step

The transport specificity of system y⁺L of human erythrocytes was investigated and the carrier was found to accept a wide range of amino acids as substrates. Relative rates of entry for various amino acids were estimated from their trans-effects on the unidirectional efflux of l-[¹⁴C]-lysine. Some neutral amino acids, l-lysine and l-glutamic acid induced marked trans-acceleration of labeled lysine efflux; saturating concentrations of external l-leucine and l-lysine increased the rate by 5.3±0.63 and 6.2±0.54, respectively. The rate of translocation of the carrier-substrate complex is less dependent on the structure of the amino acid than binding. Translocation is slower for the bulkier analogues (l-tryptophan, l-phenylalanine); smaller amino acids, although weakly bound, are rapidly transported (l-alanine, l-serine). Half-saturation constants (±sem) calculated from this effect (l-lysine, 10.32±0.49 m and l-leucine, 11.50±0.50 m) agreed with those previously measured in cis-inhibition experiments. The degree of trans-acceleration caused by neutral amino acids did not differ significantly in Na⁺, Li⁺ or K⁺ medium, whereas the affinity for neutral amino acids was dramatically decreased if Na⁺ or Li⁺ were replaced by K⁺. The observation that specificity is principally expressed in substrate binding indicates that the carrier reorientation step is largely independent of the forces of interaction between the carrier and the transport site.We wish to thank Dr C.A.R. Boyd for helpful discussions and Prof. H.N. Christensen for sharing with us very relevant bibliographic material. We are grateful to FONDECYT (1282/91) and DTI (B 2674) (Chile) for financial assistance.     

Plasma free amino acid profiles and nutrition proteins in chronic renal failure; effect of dialysis treatment

Summary A well preserved nutritional status is beneficial in chronically uremic patients for slowing the pace of deterioration of renal function, and delaying the need for dialysis therapy. The purpose of this study was to assess the nutritional profile of 10 patients in a steady state of advanced CRF, and of 15 patients with terminal renal failure immediately prior to their first hemodialysis session (J0), and 7, 14, 45, 60, days post start of dialysis. Patients were 18 to 65 years old with total plasma proteins 60g/1. Plasma concentrations of amino acids, nutrition proteins, apolipoproteins A1, and B were evaluated. Non inflammatory reaction was evaluated by determination of alpha-1-acid glycoprotein, and C reactive protein. The data (mean ± 1 SD) were compared with mean values of 15 healthy individuals.     

Chloroquine,a novel inhibitor of amino acid transport by rat renal brush border membrane vesicles

Summary Chloroquine is an antimalarial and antirheumatic lysosomotropic drug which inhibits taurine uptake into and increases efflux from cultured human lymphoblastoid cells. It inhibits taurine uptake by rat lung slices and affects the uptake and release of cystine from cystinotic fibroblasts. Speculations on its mode of action include a proton gradient effect, a non-specific alteration in membrane integrity, and membrane stabilization. In this study, the effect of chloroquine on the uptake of several amino acids by rat renal brush border membrane vesicles (BBMV) was examined. Chloroquine significantly inhibited the secondary active, NaCl-dependent component of 10µM taurine uptake at all concentrations tested, but did not change equilibrium values. Analysis of these data indicated that the inhibition was non-competitive. Taurine uptake was reduced at all osmolarities tested, but inhibition was greatest at the lowest osmolarity. Taurine efflux was not affected by chloroquine, nor was the NaCl-independent diffusional component of taurine transport. Chloroquine (1 mM) inhibited uptake of the imino acids L-proline and glycine, and the dibasic amino acid L-lysine. It inhibited the uptake of D-glucose, but not the neutral-amino acids L-alanine or L-methionine. Uptake of the dicarboxylic amino acids, L-glutamic acid and L-aspartic acid, was slightly enhanced. With regard to amino acid uptake by BBMV, these findings may support some of the currently proposed mechanisms of the action of chloroquine but further studies are indicated to determine why it affects the initial rate of active amino acid transport.     

Permeability of membranes to amino acids and modified amino acids: Mechanisms involved in translocation

Summary The amino acid permeability of membranes is of interest because they are one of the key solutes involved in cell function. Membrane permeability coefficients (P) for amino acid classes, including neutral, polar, hydrophobic, and charged species, have been measured and compared using a variety of techniques. Decreasing lipid chain length increased permeability slightly (5-fold), while variations in pH had only minor effects on the permeability coefficients of the amino acids tested in liposomes. Increasing the membrane surface charge increased the permeability of amino acids of the opposite charge, while increasing the cholesterol content decreased membrane permeability. The permeability coefficients for most amino acids tested were surprisingly similar to those previously measured for monovalent cations such as sodium and potassium (approximately 10^–12–10^–13 cm · s^–1). This observation suggests that the permeation rates for the neutral, polar and charged amino acids are controlled by bilayer fluctuations and transient defects, rather than partition coefficients and Born energy barriers. Hydrophobic amino acids were 10² more permeable than the hydrophilic forms, reflecting their increased partition coefficient values.External pH had dramatic effects on the permeation rates for the modified amino acid lysine methyl ester in response to transmembrane pH gradients. It was established that lysine methyl ester and other modified short peptides permeate rapidly (P = 10^–2 cm · s^–1) as neutral (deprotonated) molecules. It was also shown that charge distributions dramatically alter permeation rates for modified di-peptides. These results may relate to the movement of peptides through membranes during protein translocation and to the origin of cellular membrane transport on the early Earth.Abbreviations DCP dicetylphosphate - DMPC dimyristoyl phosphatidylcholine - EPC egg phosphatidylcholine - LUV large unilamellar vesicle - MLV multilamellar vesicle - PLM planar lipid membrane - SUV small unilamellar vesicle - pH transmembrane pH gradient     

Individual amino acid balances in young lean and obese Zucker rats fed a cafeteria diet

The amino acid composition of the diet ingested by reference and cafeteria diet-fed lean and obese Zucker rats has been analyzed from day 30 to 60 after birth. Their body protein amino acid composition was measured, as well as the urinary and faecal losses incurred during the period studied. The protein actually selected by the rats fed the cafeteria diet had essentially the same amino acid composition as the reference diet. The mean protein amino acid composition of the rat showed only small changes with breed, age or diet.Cafeteria-fed rats had a higher dietary protein digestion/absorption efficiency than reference diet-fed rats. Obese rats wasted a high proportion of dietary amino acids when given the reference diet, but not on the cafeteria diet. In all cases, the amino acids lost as such in the urine were a minimal portion of available amino acids.In addition to breed, the rates of protein accretion are deeply influenced by diet, but even more by the age — or size — of the animals: cafeteria-fed rats grew faster, to higher body protein settings, but later protein accrual decreased considerably; this is probably due to a limitation in the blueprint for growth which restricts net protein deposition when a certain body size is attained. Obese rats, however, kept accuring protein with high rates throughout.Diet composition — and not protein availability or quality-induced deep changes in amino acid metabolism. Since the differences in the absolute levels of dietary protein or carbohydrate energy ingested by rats fed the reference or cafeteria diets were small, it can be assumed that high (lipid) energy elicits the changes observed in amino acid metabolism by the cafeteria diet. The effects induced in the fate of the nitrogen ingested were more related to the fractional protein energy proportion than to its absolute values. Cafeteria-fed rats tended to absorb more amino acids and preserve them more efficiently; these effects were shown even under conditions of genetic obesity.There were deep differences in handling of dietary amino acids by dietary or genetically obese rats. The former manage to extract and accrue larger proportions of their dietary amino acids than the latter. The effects of both models of amino acid management were largely additive, suggesting that the mechanisms underlying the development of obesity did not run in parallel to those affecting the control of amino acid utilization. Obesity may be developed in both cases despite a completely different strategy of amino acid assimilation, accrual and utilization. (Mol Cell Biochem121: 45–58, 1993)     

Effect of regular training on the myocardial and plasma concentrations of taurine andα-amino acids in thoroughbred horses

Summary Exercise induces significant changes in the free intracellular amino acid pool in skeletal muscle but little is known of whether such changes also occur in cardiac muscle. In this study the effect of regular exercise on the size and the constituents of the free amino acid pool in the hearts and in the plasma of thoroughbred horses was investigated. The total free intracellular amino acid pool in the hearts of control horses was 30.9 ± 1.2mol/g wet weight (n = 6). Glutamine but not taurine was present at the highest concentration (13.5 ± 0.9 and 7.7 ± 0.69mol/g wet weight for glutamine and taurine respectively). As for the rest of the amino acids in the pool, only glutamate and alanine were present at levels greater than 1mol/g wet weight (4.6 ± 0.25 and 1.7 ± 0.14 for glutamate and alanine respectively). The tissue to plasma ratio was highest for taurine at 155, followed by glutamate at 111, aspartate and glutamine at 37, alanine at 5.8 and ratios of less than 3 for the rest of the amino acids. The total free intracellular amino acid pool in the hearts of exercised horses was slightly but not significantly lower than control (28.1 ±1.1mol/g wet weight, n = 6). Regular exercise increased the intracellular concentration of threonine, valine, isoleucine, leucine and phenylalanine but was only significant (p < 0.05) for threonine. This work has documented the profile of taurine and protein amino acids in the heart and in the plasma of thoroughbred horses and showed that in contrast to skeletal muscle, heart muscle does not show major changes in amino acids during regular exercise.     

Asymmetric catalysis of the Strecker amino acid synthesis by a cyclic dipeptide

Summary A novel cyclic dipeptide —cyclo[(S)-His-(S)-NorArg] — has been prepared which catalyzes an enantioselective version of the Strecker amino acid synthesis. The catalyst, when present in 2 mol % quantity in methanol solution, catalyzes the addition of hydrogen cyanide toN-alkylimines to afford-amino nitriles in high yield and high enantiomeric excess. Furthermore, acid hydrolysis ofN-benzhydryl--amino nitriles afforded the corresponding-amino acids directly. This methodology affords a variety of arylglycines in exceptionally high enantiomeric excess, but aliphatic amino acids were obtained with low enantioselectivity. Current efforts are underway to expand the scope of this reaction, as well as to elucidate the mechanism of catalysis and the roles played by substrate and catalyst in determining the stereochemical outcome of the reaction.A preliminary communication on this work has recently appeared in: Iyer MS, Gigstad KM, Namdev ND, Lipton MA (1996) J Am Chem Soc 118: 4910–4911.     

Amino acid uptake systems in lizard and chick brain cells

The uptake of seven amino acids, -aminoisobutyric acid (AIB), cyclo-leucine (cyclo-Leu), -aminobutyric acid (GABA), glycine (Gly), glutamic acid (Glu), lysine (Lys), and taurine (Tau), representatives of different amino acid transport systems, was studied in slices of brain from Tokay lizards and White Leghorn chicks. In descending order, the rate of the initial uptake of the amino acids in both species was Glu>Gly>GABA>Cyclo-Leu>AIB>Lys>Tau. The substrate specificities and the differences in sodium and temperature dependence of the uptake of the amino acids indicate the presence of several distinct amino acid transport systems, some sodium-dependent and some sodium-independent. The structural specificity of amino acid transport classes in the brain of these species is similar to that in other vertebrate brain preparations.Special issue dedicated to Dr. Santiago Grisolia.     

Differences in L-alanine uptake by livers of Wistar and lean Zucker rats

The L-alanine uptake by livers of Wistar and lean Zucker rats has been studied. The hepatic uptake and fractional extraction rates of alanine were estimated in 50–55 day old rats. No significant differences in amino acid concentrations and blood flows in afferent and efferent liver vessels were seen in lean Zucker rats when compared with Wistar rats. However, the hepatic uptake (1.6±0.1 and 0.7±0.1 mol/min/100 g bw, p<0.01) and the fractional extraction (26.8±2.1 and 15.2±3.1%, p<0.05) were much lower in Zucker than in Wistar rats. The hepatic active transport of L-alanine was determinedin vitro using isolated plasma membrane vesicles. Vesicles isolated from livers of lean Zucker rats showed similar values of Km (2.5±0.7 vs 2.0±0.5 mM for Wistar and Zucker respectively, N.S.), but lower values of Vmax when compared with Wistar rats (1.1±0.1 vs 0.6±0.005 nmol/mg prot 5 s, p<0.01, for Wistar and lean Zucker rats respectively). These results indicate that, the liver of lean Zucker rats concentrates alanine less efficiently than the liver of Wistar rats. This fact correlates well with a lower capacity of the Na⁺-dependent L-alanine trasport in liver plasma membrane vesicles from lean Zucker rats.