Aspects of D-leucine and D-lysine metabolism in maize and ryegrass seedlings

Summary Maize and ryegrass seedlings (2.5 weeks old), the roots of which were dipped into 10^-3M ¹⁴C-carboxyl-labeled D-leucine and ¹⁴C--labeled D-lysine, readyly absorbed and converted or conjugated within 34 hr some 75–90% of the labeled compound supplied. The metabolic intermediates and products were generally similar for both maize and ryegrass. Radioactive intermediates from the carboxyllabeled D-leucine were L-leucine, N-malonyl-D-leucine (provisionally identified), and -ketoisocaproic acid. Intermediates from -labeled D-lysine were numerous, with greater amounts and numbers detected in roots than in tops. Pipecolic acid was a major intermediate particularly in shoot tissue.Pathways of conversion appeared analogous to those for the L-isomer, and conversion may be by the usual L-configuration machinery, since the labeled L-isomer of the originally supplied ¹⁴C-D-amino acid was always found. How the ¹⁴C-D-amino acid gets to ¹⁴C-L-isomer is not known, but finding significant proportions of unlabeled D-alanine in plants treated with both the labeled L-leucine and D-lysine suggested that formation of the -keto-acid analog and subsequent reamination was possibly an important route.Approved for publication as Technical Paper No. 2,729 of the Oregon Agricultural Experiment Station.Trade, copyright or company names are for identification and reader benefit; their use does not constitute endorsement or preferential treatment by the U.S.D.A.Respectively, Research Associate, Department of Soils, Oregon State University; Research Chemist, Soil and Water Conservation Research Division, Agricultural Research Service, U.S. Department of Agriculture. Present address of senior author: Institut für Bodenkunde D-3400 Göttingen, von Sieboldstraße 4, West Germany.—We thank the Oregon State University Research Council and the Bundesministerium für Ernährung, Landwirtschaft und Forsten, Bonn, Germany, for partial financial assistance to the senior author, and M. Yamamoto for technical assistance.     

Some physiological functions of the L-leucine dehydrogenase in Bacillus subtilis

Mutants of Bacillus subtilis constitutive for L-leucine dehydrogenase synthesis were selected. Using these mutants we could determine two functional roles for the L-leucine dehydrogenase. This enzyme liberates ammonium ions from branched chain amino acids when supplied as the sole nitrogen source. Another function is to synthesize from L-isoleucine, L-leucine, and L-valine the branched chain -keto acids which are precursors of branched chain fatty acid biosynthesis. These results together with the inducibility of the enzyme suggest that the L-leucine dehydrogenase has primarily a catabolic rather than an anabolic function in the metabolism of Bacillus subtilis.     

Testing the Hypothesis that System y<Superscript>+</Superscript>L Accounts for High- and Low-Transport Phenotypes in Chicken Erythrocytes Using <Emphasis Type="SmallCaps">L</Emphasis>-Leucine as Substrate

Experiments were carried out to test the hypothesis that system y⁺L accounts for the high (HT) and low (LT) amino-acid transport phenotypes in chicken erythrocytes and to explain the different effect of selective breeding on lysine and leucine fluxes. L-Leucine transport was characterized in individuals which had been separated into two groups (HT and LT) according to their capacity to transport L-lysine across the erythrocyte membrane. Whereas lysine influx (1 μM) in the two groups differed by 32-fold (HT/LT), leucine influx was not significantly different. Average rates (nmol/ L cells/ min) were: 227 (HT) and 7.0 (LT) for L-lysine, and 8.9 (HT) and 7.1 (LT) for L-leucine. The differential ability of L-lysine and L-leucine fluxes to discriminate between the HT and LT phenotypes was shown to be consistent with the interactions of these substrates with system y⁺L and to vary depending on the conditions of the assay. It is shown that the two phenotypes can be clearly discriminated by measuring L-leucine influx in the presence of Li⁺. These results support the hypothesis that the HT and LT phenotypes reflect alterations in the function of system y⁺L and illustrate that the choice of the appropriate substrate and medium composition must be carefully considered when investigating the consequences of either experimental or natural alterations of broad-scope transporters.     

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.     

Detection of a single,metal-independent aminopeptidase activity in polymyxin-extracts from Escherichia coli B

Summary The supernatant of Escherichia coli B autolysed in the presence of polymyxin B contains a single, metal-independent aminopeptidase activity (E.C.-group 3.4.1). The enzyme cleaves the 4-nitroanilides of L-alanine, L-lysine, L-leucine, glycine, and weakly L-phenylalanine. The corresponding N-acetyl-L-alanine-, L-glutamic acid- and L-cysteine-derivatives are not attacked.Dedicated to Dr. Hans Poschenrieder on the occasion of his 75th birthday.     

Chemotaxis and transport of amino acids in Allomyces arbuscula

Among a number of amino acids tested, l-lysine and l-arginine are the principal attractants in the chemotaxis of the zygotes of Allomyces arbuscula. The reaction can be stimulated to a greater or lesser extent by a number of compounds chemically related to l-leucine. No relationship between transport of attracting amino acids and their effect on chemotaxis has been found.     

Influence of amino acids on the biosynthesis of cyclosporin A by Tolypocladium inflatum

 An indigenously isolated strain of Tolypocladium inflatum, when grown as a suspension culture in semi-synthetic and synthetic media, produced cyclosporin A. Biosynthesis of this well-known immunosuppressive agent was found to be influenced heavily by the external addition of the amino acid constituents of the molecule. In synthetic media, L-leucine and L-valine were found to act as strong inducers of drug production. L-Valine increased the specific production of cyclosporin A by 75% in semi-synthetic medium and by ten times in synthetic medium compared to an unsupplemented control culture. D-Valine had no stimulating effect on the production. The presence of amino acids in the exponential growth phase ensured optimal production, as was indicated in the experiment in which L-valine was added at different times; 4 g/l was the optimum concentration of exogenous L-valine. On the other hand, exogenous sarcosine and L-methionine tended to diminish drug production. Received: 23 October 1995/Received revision: 23 January 1996/Accepted: 29 January 1996     

Transport of basic amino acids and regulation of aspartate kinase activity in thialysine andL-canavanine resistant strains ofSerratia marcescens

Growth ofSerratia marcescens was not inhibited by high concentrations ofL-lysine and its structural analogues,L-canavanine and S-(2-aminoethyl)-L-cysteine (thialysine). This insensitivity was not caused by deficient transport of basic amino acids, unlike in mutant strains ofEscherichia coli having the same properties. The tested strains showed a lack of regulation at the aspartate kinase level towardL-lysine and thialysine. The data indicate great intraspecific variability for aspartate kinase regulation inS. marcescens.     

Uptake of amino acids by actidione-treated yeast cells

Uptake of glyeine,l-cysteine,l-leucine,l-methionine,l-aspartic acid andl-lysine was investigated in resting cells ofSaccharomyces cerevisiae treated with 0.3mm actidione for blocking protein synthesis. The amino acids were taken up against substantial concentration gradients (up to nearly 1,000∶1 for μm l-cysteine and glycine). They were present in the free form inside the cells. Their unidirectional transmembrane fluxes were under a negative feedback control by the intracellular concentration of the amino acid involved. The amino acids tested apparently employed more than one transport agéncies for their membrane passage, the half-saturation constants being 6.2–7.7×10⁻⁴ m for glycine, 2.5×10⁻⁴ m forl-cysteine, 6×10⁻⁵ and 4×10⁻⁴ m forl-lysine, 3×10⁻⁵ and 6×10⁻⁴ m forl-methionine, 7–18×10⁻⁵ and 1.6×10⁻³ m forl-aspartic acid and 6×10⁻⁵ and 2×10⁻³ m forl-leucine. The specificities of the transport systems are overlapping but there emerges a wide-affinity transport system for glycine, alanine, leucine, methionine, serine, cysteine, phenylalanine, aspartic acid, asparagine, glutamic acid and tryptophan (and possibly for other amino acids), and more specific systems for each of the following: glycine, lysine, methionine, histidine, arginine, and aspartic and glutamic acids. Proline had the peculiar effect of stimulating the transport of all the amino acids tested. The amino acids apparently interacted in the uptake not only by competition for the binding site but also by allotopic inhibition (e.g.l-cysteine) and possibly stimulation (l-proline). The initial rate of uptake of amino acids and their steady-state level of distribution were characterized by identical activation energies: 7.5 kcal/mole forl-lysine, 6.9 kcal/mole forl-aspartic acid, and 13.2 kcal/mole for glycine.     

New Resolving Agents

Seven optical active 2-benzylamino alcohols were synthesized by reduction of N-benzoyl derivatives of L-alanine, L-valine, L-leucine, L-phenylalanine, L-aspartic acid, L-glutamic acid and L-lysine and applied for the resolution of (±)-trans-chrysanthemic acid. d-trans-Chrys-anthemic acid was obtained by resolution via the salts of 2-benzylamino alcohols derived from L-valine and L-leucine, while (?)-trans-chrysanthemic acid was prepared through the salts of the amino alcohols derived from L-alanine and L-phenylalanine.     

Characterization of an alkaline protease from Bacillus sp. no. AH-101

Summary The Bacillus sp. no. AH-101 alkaline protease showed higher hydrolysing activity against insoluble fibrous natural proteins such as elastin and keratin in comparison with subtilisins and Proteinase K. The optimum pH of the enzyme toward elastin and keratin was pH 10.5 and pH 11.0–12.0 respectively. The specific activity toward elastin and keratin was 10 600 units/mg protein and 3970 units/mg protein, respectively. The enzymatic activity was not inhibited by p-chloromercuribenzoic acid and iodoacetic acid. Carbobenzoxy-glycyl-glycyl-L-phenylalanyl chloromethyl ketone completely inhibited the caseinolytic activity, but 36% elastolytic activity remained. No inhibitory effect on caseinolytic and elastolytic activity was shown by tosyl-L-phenylalanyl-chloromethyl ketone, tosyl-L-lysine chloromethyl ketone, carbobenzoxy-L-phenylalanyl chloromethyl ketone, and elastatinal. The amino acid composition and amino terminal sequence of the enzyme were determined. The no. AH-101 alkaline protease was compared with subtilisin BPN', subtilisin Carlsberg, no. 221, and Ya-B alkaline proteases. Extensive sequence homology existed among these enzymes. Offprint requests to: H. Takami     

ɛ-Poly-<Emphasis Type="SmallCaps">l</Emphasis>-lysine producer, <Emphasis Type="Italic">Streptomyces albulus</Emphasis>, has feedback-inhibition resistant aspartokinase

Streptomyces albulus NBRC14147 produces ɛ-poly-l-lysine (ɛ-PL), which is an amino acid homopolymer antibiotic. Despite the commercial importance of ɛ-PL, limited information is available regarding its biosynthesis; the l-lysine molecule is directly utilized for ɛ-PL biosynthesis. In most bacteria, l-lysine is biosynthesized by an aspartate pathway. Aspartokinase (Ask), which is the first enzyme in this pathway, is subject to complex regulation such as through feedback inhibition by the end-product amino acids such as l-lysine and/or l-threonine. S. albulus NBRC14147 can produce a large amount of ɛ-PL (1–3 g/l). We therefore suspected that Ask(s) of S. albulus could be resistant to feedback inhibition to provide sufficient l-lysine for ɛ-PL biosynthesis. To address this hypothesis, in this study, we cloned the ask gene from S. albulus and investigated the feedback inhibition of its gene product. As predicted, we revealed the feedback resistance of the Ask; more than 20% relative activity of Ask was detected in the assay mixture even with extremely high concentrations of l-lysine and l-threonine (100 mM each). We further constructed a mutated ask gene for which the gene product Ask (M68V) is almost fully resistant to feedback inhibition. The homologous expression of Ask (M68V) further demonstrated the increase in ɛ-PL productivity.     

Lysine degradation in Candida maltosa: occurrence of a novel enzyme,acetyl-CoA: L-lysine N-acetyltransferase

The yeast Candida maltosa can utilize L-lysine as sole nitrogen and sole carbon source accompanied by accumulation of -N-acetyl-L-lysine, indicating that lysine is metabolized by way of N-acetylated intermediates. A novel lysine acetyltransferase catalyzing the first step in this pathway, the N-acetylation of the -amino group of L-lysine, was found in this yeast. The enzyme, acetyl-CoA:L-lysine N-acetyltransferase, is strongly induced in cells grown on L-lysine as sole carbon source. The enzyme is specific for both L-lysine and acetyl-CoA. The K _m values are 10 mM for L-lysine and 0.33 mM for acetyl-CoA. The enzyme has a maximum activity at pH 8.1.Dedicated to Prof. Dr. F. Böttcher in occasion of his 60th birthday     

Biosynthesis ofL-lysine inCorynebacterium glutamicum on sucrose,ethanol and acetic acid

Production ofL-lysine was followed in two lysine-accumulating mutants ofCorynebacterium glutamicum ATCC 13287 in media containing sucrose, ethanol, acetic acid or a mixture of acetic acid and ammonium or sodium acetate. It was found that acetate is the best substitution for sucrose.     

Modification of materials formed from poly(L-lactic acid) to enable covalent binding of biopolymers: Application to high-density three-dimensional cell culture in foams with attached collagen

Summary We describe a method for increasing the hydrophilicity of materials formed from biodegradable polymers and introducing chemical functional groups on their surfaces. Poly(L-lactic acid) was blended with poly(ɛ-CBZ-L-lysine) at an 80:20 ratio. Films of the mixture were prepared and foams were made by solvent casting and salt leaching. Amino groups on the surface of the polymer mixture were deprotected by acid hydrolysis. As an example of the applicability of the technique for attachment of biomolecules, we covalently linked collagen to the deprotected amino groups, creating a surface capable of high density growth of a differentiated cell type (bovine adrenocortical cells). The method should be generally useful for surface modification of biodegradable polymer materials used in tissue engineering.     

Effect of adding dietary L-lysine, L-threonine and L-methionine to a low gluten diet on urea synthesis in rats

Summary. We have shown that urinary urea excretion increased in rats fed a low quality protein. The purpose of present study was to determine whether an addition of dietary limiting amino acids affected urea synthesis in rats fed a low gluten diet. Experiments were done on three groups of rats given diets containing 10% gluten, 10% gluten+0.5% L-lysine or 10% gluten+0.5% L-lysine, 0.2% L-threonine and 0.2% L-methionine for 10d. The urinary excretion of urea, and the liver concentrations of serine and ornithine decreased with the addition of dietary L-lysine, L-threonine and L-methionine. The fractional and absolute rates of protein synthesis in tissues increased with the treatment of limiting amino acids. The activities of hepatic urea-cycle enzymes was not related to the urea excretion. These results suggest that the addition of limiting amino acids for the low gluten diet controls the protein synthesis in tissues and hepatic ornithine and decline urea synthesis.     

Preferential production of rapamycin vs prolylrapamycin by Streptomyces hygroscopicus

A trace of prolylrapamycin is often produced in rapamycin fermentations carried out by strains of Streptomyces hygroscopicus. Prolylrapamycin was produced as the major rapamycin when L-proline was added to the fermentation medium. Addition of proline plus thiazolidine-2-carboxylic acid (T2CA), a sulfur-containing proline analog, prevented rapamycin production and stimulated prolylrapamycin production, thereby resulting in an even greater selective production of prolylrapamycin. T2CA addition inhibited rapamycin production even in the presence of L-lysine which is converted into pipecolic acid intracellularly and normally stimulates rapamycin formation. Addition of the rapamycin precursor, DL-pipecolic acid, surprisingly failed to stimulate rapamycin production. However, when DL-pipecolic acid was added with L-proline, it reduced the formation of prolylrapamycin and stimulated rapamycin production; this was evident especially in the presence of T2CA. The evidence suggests that T2CA suppresses rapamycin production by inhibiting intracellular conversion of L-lysine into pipecolate. Furthermore, the data suggest that uptake of pipecolate into the cell is stimulated or induced by growth in the presence of L-proline and/or T2CA. Received 24 December 1997/ Accepted in revised form 12 May 1998     

Uptake of leucine,lysine, aspartic acid,and glycine into isolated neurons and astrocytes

The uptake of tritium-labeledl-leucine,l-lysine,l-aspartic acid, and glycine by neurons and astrocytes isolated from the cerebral cortex of 3-week-old rats was followed for varying periods up to 40 min at amino acid concentrations from 1 to 2000 mol/liter in medium. The effects of a low-sodium (15.5 mmol/liter) medium on the uptake were also studied. The influx of the amino acids was faster into astrocytes than into neurons. Leucine penetrated into the cells faster than the other amino acids. Amino acid transport was mainly saturable at the lowest amino acid concentrations studied, whereas nonsaturable penetration into the cells dominated in the millimolar concentration range. The saturable transport comprised only one transport system with relatively small transport constants, resembling in nature the so-called high-affinity transport. The maximal velocities of transport were about two times higher in astrocytes than in neurons. In neurons the partial substitution of sodium by choline in medium had the most effect in reducing the influx of glycine and aspartic acid. In astrocytes the effects were generally less pronounced. The results suggest that extracellular amino acids generally penetrate more readily into astrocytes than into neurons. Both cell types transport essential amino acids more effectively than other amino acids.     

l-leucine dehydrogenase fromBacillus cereus

Summary An improved method for the production ofl-leucine dehydrogenase is described employing a mutant with a constitutive enzyme and a fed-batch cultivation technique yielding high cell concentrations. Purification ofl-leucine dehydrogenase to homogeneity was carried out starting with 30 kgBacillus cereus cells by heat treatment at 63°C, followed by two liquid-liquid extraction steps and three conventional column chromatographies. Crystals have been obtained from the 95-fold purified enzyme. The molecular weight of the native enzyme was determined by sedimentation equilibrium and gel filtration studies to be 310 000 containing eight identical subunits with a molecular weight of 39 000. The sedimentation coefficient was estimated to 11.65 S. Branched-chain amino acids likel-leucine,l-valine orl-isoleucine are deaminated by the NAD-dependent enzyme. In the reverse reaction a variety of 2-ketoacids, especially 2-ketoisocaproate, 2-ketoisovalerate and 2-keto-3-methyl-valerate, were reductive aminated to the correspondingl-amino acids in the presence of 0.9 M ammonia. The amino acid composition for the subunit ofl-leucine dehydrogenase is presented.     

S-methyl thioesters are produced from fatty acids and branched-chain amino acids by brevibacteria: focus on L-leucine catabolic pathway and identification of acyl-CoA intermediates

Despite their importance as potent odors that contribute to the aroma of numerous cheeses, S-methyl thioesters formation pathways have not been fully established yet. In a first part of our work, we demonstrated that Brevibacterium antiquum and Brevibacterium aurantiacum could produce S-methyl thioesters using short-chain fatty acids or branched-chain amino acids as precursors. Then, we focused our work on l-leucine catabolism using liquid chromatography tandem mass spectrometry and gas chromatography-mass spectrometry analyses coupled with tracing experiments. For the first time, several acyl–CoAs intermediates of the l-leucine to thioesters conversion pathway were identified. S-methyl thioisovalerate was produced from l-leucine, indicating that this amino acid was initially transaminated. Quite interestingly, data also showed that other S-methyl thioesters, e.g., S-methyl thioacetate or S-methyl thioisobutyrate, were produced from l-leucine. Enzymatic and tracing experiments allowed for postulating catabolic pathways leading to S-methyl thioesters biosynthesis.