Diminished arginine-stimulated insulin secretion in trained men

Glucose-stimulated insulin secretion is depressed by training. To further elucidate the beta-cell adaptation to training, a nonglucose secretagogue was applied. Arginine was infused for 90 min to seven trained and seven untrained young men. Arginine and glucose concentrations increased identically in the groups. The insulin response was biphasic and waned despite increasing arginine concentrations. Both these phases as well as C-peptide responses were reduced in trained subjects, whereas proinsulin responses were similar in the groups. Identical increases were found in glucagon, growth hormone, catecholamines, and production and disappearance of glucose; identical decreases were found in free fatty acids, glycerol, and beta-hydroxybutyrate. In conclusion, in men training diminishes both arginine- and glucose-stimulated insulin secretion, indicating a profound beta-cell adaptation. Being enhanced, the effects of insulin on both production and disposal of glucose are changed in the opposite direction to beta-cell secretion by training. The responses of glucagon- and growth hormone-secreting cells to arginine do not change with training.     

Amino acid transport in whole cells and membrane vesicles of Arthrobacter pyridinolis

Arginine, and several other amino acids, can only support growth of Arthrobacter pyridinolis if malate is also present in the medium. Arginine is transported by a high affinity lysine-arginine-ornithine-type transport system which is stimulated by malate in both whole cells and vesicles, is respiration-coupled, and appears to depend upon a respiration-generated membrane potential but not on a ΔpH. Arginine is also transported by a low-affinity system which transports canavanine. Studies of an arginine auxotroph suggest that the lysine-arginine-ornithine system may be the system of major physiological significance for arginine transport. Phenylalanine is one of a few amino acids which can act as sole source of carbon for A. pyridinolis. Transport of phenylalanine occurs by two kinetically distinct systems. Both of these transport systems are respiration-coupled, are not appreciably stimulated by malate either in cells or vesicles, but are markedly stimulated by ascorbate-phenazine methosulfate. Studies with inhibitors indicate that the transport systems for phenylalanine utilize both a ΔpH and a membrane potential.     

Desensitization of immature rat testicular ornithine decarboxylase to arginine vasopressin

Prior exposure of immature rat testis to arginine vasopressin caused the testis refractory at 24 h in terms of ornithine decarboxylase activity. Arginine vasopressin caused desensitization both in Leydig cells and seminiferous tubules. Arginine vasopressin induced desensitization was found to be both time and dose-dependent. Arginine vasopressin desensitized testis was refractory to luteinizing hormone, follicle stimulating hormone, norepinephrine, dibutyryl cAMP, phorbol-myristate acetate and cholera toxin at 24 h. Arginine vasopressin desensitized testis showed recovery of response to norepinephrine at 48 h after the first injection. On the contrary arginine vasopressin could stimulate ornithine decarboxylase in luteinizing hormone desensitized testis. These results indicate that in arginine vasopressin desensitized testis the block is at post cAMP step which is common to both cAMP dependent and protein kinase C-diacylglycerol system in stimulating testicular ornithine decarboxylase.     

Studies on the Nitrogen Metabolism in Ectomycorrhizae

Concentrations of free and bound amino acids were determined in 1) the mycorrhizal fungus Boletus variegatus Fr. 2) nonmycorrhizal root systems of aseptically grown Pinus sylvestris L. seedlings, and 3) mycorrhizal root systems of seedlings developed aseptically using the two symbionts. Arginine (total) was the major amino acid constituent in the mycelium of B. variegatus (18%–22%) during the exponential phase of growth. While 59%–86% of the available arginine was bound during the acceleration phase of growth, in the logarithmic phase 63%–75% was in the free pool. There were differences in the proportions between the individual amino acids in the bound fraction at different stages of growth suggesting production of diverse proteins. Twenty per cent of the amino acid content of uninfected P. sylvestris root systems was arginine. Infection of the root systems by the fungal symbiont did not result in an increase but a slight decrease in the free arginine content of the composite structure. Almost all other amino acids in the free pool were found in higher concentrations in the mycorrhizal root system. It is suggested that arginine synthesis in B. variegatus is repressed by the arginine available in the host. The mycorrhizal fungus possibly metabolizes the host arginine pool ultimately resulting in more efficient protein synthesis in both the partners.     

Control of the flux to arginine in Neurospora crassa: de-repression of the last three enzymes of the arginine pathway

The steady state concentrations of arginine and related intermediary metabolites of the arginine biosynthetic pathway in the eukaryote Neurospora crassa were varied and the concurrent de-repression of the enzymes ornithine transcarbamylase, argininosuccinate synthetase and argininosuccinase was measured. Pool variation was achieved endogenously by the introduction and combination of mutant enzymes with reduced specific activities. Measurements of activities of the mutationally unaltered enzymes showed various degrees of de-repression. The highest activity level for each of the three enzymes was about five times that found in the fully repressed wild-type strain. The variations observed in the pools were as follows: ornithine, 7-fold; citrulline, 700-fold; argininosuccinic acid, 400-fold; arginine, 300-fold.By this means a quantitative analysis of the process of repression is made possible. A strong correlation was found between the degree of de-repression of the three enzymes and the concentration of arginine. The de-repression follows a sigmoid curve with respect to arginine concentration. This is consistent with the interpretation that the pathway enzymes are subject to a repression system with arginine, or a simple derivative of it, acting as a co-repressor.     

Role and Regulation of Bacillus subtilis Glutamate Dehydrogenase Genes

The complete Bacillus subtilis genome contains two genes with the potential to encode glutamate dehydrogenase (GlutDH) enzymes. Mutations in these genes were constructed and characterized. The rocG gene proved to encode a major GlutDH whose synthesis was induced in media containing arginine or ornithine or, to a lesser degree, proline and was repressed by glucose. A rocG null mutant was impaired in utilization of arginine, ornithine, and proline as nitrogen or carbon sources. The gudB gene was expressed under all growth conditions tested but codes for a GlutDH that seemed to be intrinsically inactive. Spontaneous mutations in gudB that removed a 9-bp direct repeat within the wild-type gudB sequence activated the GudB protein and allowed more-efficient utilization of amino acids of the glutamate family.     

The effect of glucose on antidiuretic hormone absorption in the rat and frog small intestine

Administration of 5 ml/100 g body weight of 1% glucose solution to stomach produced the same diuretic kidney response in fasted Wistar rats as administration of the same amount of water. Intragastric administration of arginine vasopressin along with the water load evoked an antidiuretic response. Arginine vasopressin in the same volume of glucose induced no kidney response difference as compared with the hormone action in experiments with water load. 0.1 nmol of arginine vasotocin, having been itroduced into the rat isolated ileum, prevented the effect of glucose on the hormone absoption. 0.1 nmol of arginine vasotocin, having been introduced into the frog isolated ileum along with isotonic glucose solution, increased the hormone absorption; fructose did not affect this process whereas mannitol decreased absorption ofarginine vasotocin. This absorption was also reduced by intraileal introduction of arginine vasotocin with the hypotonic Ringer solution. The findings suggest that glucose in the rat gastrointestinal tract does not affect arginine vasopressin absorption in vivo, whereas in the frog ileum glucose increases arginine vasotocin absorption in vitro.     

Crystal structure of shrimp arginine kinase in binary complex with arginine—a molecular view of the phosphagen precursor binding to the enzyme

Arginine kinase (AK) is a key enzyme for energetic balance in invertebrates. Although AK is a well-studied system that provides fast energy to invertebrates using the phosphagen phospho-arginine, the structural details on the AK-arginine binary complex interaction remain unclear. Herein, we determined two crystal structures of the Pacific whiteleg shrimp (Litopenaeus vannamei) arginine kinase, one in binary complex with arginine (LvAK-Arg) and a ternary transition state analog complex (TSAC). We found that the arginine guanidinium group makes ionic contacts with Glu225, Cys271 and a network of ordered water molecules. On the zwitterionic side of the amino acid, the backbone amide nitrogens of Gly64 and Val65 coordinate the arginine carboxylate. Glu314, one of proposed acid–base catalytic residues, did not interact with arginine in the binary complex. This residue is located in the flexible loop 310–320 that covers the active site and only stabilizes in the LvAK-TSAC. This is the first binary complex crystal structure of a guanidine kinase in complex with the guanidine substrate and could give insights into the nature of the early steps of phosphagen biosynthesis.     

Arginine kinase is highly expressed in the compound eye of the honey-bee,Apis mellifera

We have cloned and sequenced a 1.68-kb cDNA encoding arginine kinase in the honey-bee, Apis mellifera. The predicted protein shows a high level of identity to known arginine kinases in invertebrates and to other proteins belonging to the conserved family of ATP: guanidino phospho-transferases. The pattern of expression of arginine kinase has been investigated for the first time in various tissues including the brain, antennae and compound eye. Our results show that three isoforms of arginine kinase, transcribed from a single gene, are expressed in a characteristic pattern in major tissues of the honey-bee. Arginine kinase mRNA is relatively abundant in the central nervous system and in the antennae. However, the highest level of expression, that is at least two to three times higher than in the brain, is found in the compound eye of the bee. By contrast, the levels of mRNAs encoding another metabolically important enzyme, a-glycerolphosphate dehydrogenase (a-GPDH), are low in the eye. These findings suggest that arginine kinase is an important component of the energy releasing mechanism in the visual system that has high and fluctuating energy demands. Furthermore, our results support the role of phosphagen kinases in energy transport in polarised cells and are consistent with the role of arginine kinase as an energy shuttle that delivers ATP generated by mitochondria to high energy-requiring processes, such as massive membrane turnover and pigment regeneration in the retina.     

Growth and spore germination factors of various strains of Bacillus sphaericus

The work was aimed at studying the requirements of sixteen Bacillus sphaericus strains with a different larvicidal activity in amino acids and some other compounds necessary for their growth and spore germination. Most of the strains were found to require arginine, glutamate, methionine, threonine, serine, glycine, alanine and lysine, but they did not assimilate phenylalanine and proline. Arginine, methionine and glutamate were shown to be the most effective inductors of spore germination. Specific differences were detected in the requirements of virulent and avirulent strains. Glucose repressed both spore germination and spore formation.     

Improved method for expression and isolation of the Mycoplasma hominis arginine deiminase from the recombinant strain of Escherichia coli

Arginine deiminase is a promising anticancer drug active against melanoma, hepatocarcinoma and other tumors. Recombinant strains of Escherichia coli that express arginine deiminase from pathogenic bacteria Mycoplasma have been developed. However, production costs of heterologous arginine deiminase are high due to use of an expensive inducer and extraction buffer, as well as using diluted culture for enzyme induction. We report on a new advanced protocol for Mycoplasma hominis arginine deiminase expression, extraction and renaturation. The main improvements include manipulation with dense suspensions of E. coli, use of lactose instead of isopropyl β-d-1-thiogalactopyranoside as an inducer and a cheaper but not less efficient buffer for solubilization of arginine deiminase inclusion bodies. In addition, supplementation of the storage culture medium with glucose and substrate (arginine) significantly stabilized the recombinant arginine deiminase producer. Homogenous preparations of recombinant arginine deiminase were obtained using anion-exchange and hydrophobic chromatography. The purified enzyme retained a specific activity of 30–34 U/mg for 12 months when stored at 4 °C in 20 mM sodium phosphate buffer pH 7.2 containing 1 M NaCl.     

Extent of Genetic Lesions of the Arginine and Pyrimidine Biosynthetic Pathways in Lactobacillus plantarum, L. paraplantarum, L. pentosus, and L. casei: Prevalence of CO2-Dependent Auxotrophs and Characterization of Deficient arg Genes in L. plantarum

Lactic acid bacteria require rich media since, due to mutations in their biosynthetic genes, they are unable to synthesize numerous amino acids and nucleobases. Arginine biosynthesis and pyrimidine biosynthesis have a common intermediate, carbamoyl phosphate (CP), whose synthesis requires CO₂. We investigated the extent of genetic lesions in both the arginine biosynthesis and pyrimidine biosynthesis pathways in a collection of lactobacilli, including 150 strains of Lactobacillus plantarum, 32 strains of L. pentosus, 15 strains of L. paraplantarum, and 10 strains of L. casei. The distribution of prototroph and auxotroph phenotypes varied between species. All L. casei strains, no L. paraplantarum strains, two L. pentosus strains, and seven L. plantarum strains required arginine for growth. Arginine auxotrophs were more frequently found in L. plantarum isolated from milk products than in L. plantarum isolated from fermented plant products or humans; association with dairy products might favor arginine auxotrophy. In L. plantarum the argCJBDF genes were functional in most strains, and when they were inactive, only one gene was mutated in more than one-half of the arginine auxotrophs. Random mutation may have generated these auxotrophs since different arg genes were inactivated (there were single point mutations in three auxotrophs and nonrevertible genetic lesions in four auxotrophs). These data support the hypothesis that lactic acid bacteria evolve by progressively loosing unnecessary genes upon adaptation to specific habitats, with genome evolution towards cumulative DNA degeneration. Although auxotrophy for only uracil was found in one L. pentosus strain, a high CO₂ requirement (HCR) for arginine and pyrimidine was common; it was found in 74 of 207 Lactobacillus strains tested. These HCR auxotrophs may have had their CP cellular pool-related genes altered or deregulated.     

Arginine supplementation and exposure time affects polyamine and glucose metabolism in primary liver cells isolated from Atlantic salmon

Arginine has been demonstrated to enhance glucose and lipid oxidation in mammals through activation of polyamine turnover. We aimed to investigate how arginine affects energy utilization through polyamine metabolism and whether this effect is time dependent. Primary liver cells were isolated from Atlantic salmon (2.2 kg body weight) fed diets containing 25.5 (low arginine, LA) or 36.1 (high arginine, HA) g arginine/kg dry matter for 12 weeks, to investigate the effect of long-term arginine supplementation. The cells were cultured for 24 h in L-15 medium to which either alpha-difluoromethylornithine (DFMO) or N ¹,N ¹¹-diethylnorspermine (DENSPM) was added. Analysis of the medium by nuclear magnetic resonance revealed significant differences between the two dietary groups as well as between cells exposed to DFMO and DENSPM, with decreased glucose, fumarate and lactate concentrations in media of the HA cells. Liver cells from fish fed the HA diet had higher spermidine/spermine-N1-acetyltransferase protein abundance and lower adenosine triphosphate concentration as compared to the LA-fed fish, while gene expression was not affected by either diet or treatment. Primary liver cells isolated from salmon fed a commercial diet and cultured in L-15 media with or without arginine supplementation (1.82 or 3.63 mM) for 48 h, representing short-term effect of arginine supplementation, showed differential expression of genes for apoptosis and polyamine synthesis due to arginine supplementation or inhibition by DFMO. Overall, arginine concentration and exposure time affected energy metabolism and gene regulation more than inhibition or activation of key enzymes of polyamine metabolism, suggesting a polyamine-independent influence of arginine on cellular energy metabolism and survival.     

Mechanisms and specificity of amino acid transport in Taenia crassiceps larvae (Cestoda)

The absorption of lysine, arginine, phenylalanine and methionine by Taenia crassiceps larvae is linear with respect to time for at least 2 min. Arginine uptake occurs by a mediated system and diffusion, and arginine, lysine and ornithine (in order of decreasing affinity) are completely competitive inhibitors of arginine uptake. The basic amino acid transport system has a higher affinity for l-amino acids than d-amino acids, and blocking the α-amino group of an amino acid destroys its inhibitory action. Phenylalanine uptake by T. crassiceps larvae is inhibited in a completely competitive fashion by serine, leucine, alanine, methionine, histidine, phenylalanine, tyrosine and tryptophan (in order of increasing affinity). Methionine apparently binds non-productively to the phenylalanine (aromatic amino acid-preferring) transport system. l-methionine uptake by larvae is inhibited more by d-alanine and d-valine than by their respective l-isomers, while d- and l-methionine inhibit l-methionine uptake equally well. The presence of an unsubstituted α-amino group is essential for an inhibitor to have a high affinity for the methionine transport system. Uptake of arginine, phenylalanine and methionine is Na⁺-insensitive, and both phenylalanine and methionine are accumulated by larvae against a concentration difference in the presence or absence of Na⁺. Arginine accumulation is precluded by its rapid metabolism to proline, ornithine and an unidentified compound.     

Nitrogen regulation of arginase in Neurospora crassa.

The final products of the arginine catabolism that can be utilized as a nitrogen source in Neurospora crassa are ammonium, glutamic acid, and glutamine. The effect of these compounds on arginase induction by arginine was studied. In wild-type strain 74-A, induction by arginine was almost completely repressed by glutamic acid plus ammonium, whereas ammonium or glutamic acid alone had only moderate effects. Arginine products of catabolism also repressed arginase induction. A mutant, ure-1, which lacks urease activity, hyperinduced its arginase with arginine as a nitrogen source. The addition of either ammonium or glutamine produced effects similar to those in the wild-type strain. The effect of ammonium on arginase induction is mediated through its conversion into glutamine. This was demonstrated in mutant am-1, which lacks L-glutamate dehydrogenase activity. In this mutant, the effect of glutamic acid was reduced, and, with ammonium, it was completely lost. The addition of glutamine or glutamic acid plus ammonium to this strain decreased by threefold the induction of arginase by arginine. Proline, a final product of arginine catabolism, competitively inhibited arginase activity. This effect and the repression of arginase by glutamine are examples of negative modulation of the first enzyme in a catabolic pathway by its final products.     

Modulation of the Arginase Pathway in the Context of Microbial Pathogenesis: A Metabolic Enzyme Moonlighting as an Immune Modulator

Arginine is a crucial amino acid that serves to modulate the cellular immune response during infection. Arginine is also a common substrate for both inducible nitric oxide synthase (iNOS) and arginase. The generation of nitric oxide from arginine is responsible for efficient immune response and cytotoxicity of host cells to kill the invading pathogens. On the other hand, the conversion of arginine to ornithine and urea via the arginase pathway can support the growth of bacterial and parasitic pathogens. The competition between iNOS and arginase for arginine can thus contribute to the outcome of several parasitic and bacterial infections. There are two isoforms of vertebrate arginase, both of which catalyze the conversion of arginine to ornithine and urea, but they differ with regard to tissue distribution and subcellular localization. In the case of infection with Mycobacterium, Leishmania, Trypanosoma, Helicobacter, Schistosoma, and Salmonella spp., arginase isoforms have been shown to modulate the pathology of infection by various means. Despite the existence of a considerable body of evidence about mammalian arginine metabolism and its role in immunology, the critical choice to divert the host arginine pool by pathogenic organisms as a survival strategy is still a mystery in infection biology.     

Enzymatic synthesis of arginine phosphate with coupled ATP cofactor regeneration

Arginine phosphate, a compound having high phosphate transfer potential which occurs in invertebrates, has been prepared in a 2-mol scale by enzymatic synthesis from arginine and ATP using arginine kinase as catalyst. ATP was regenerated in situ, using phosphoenolpyruvate or acetylphosphate as the ultimate phosphate donors.     

Utilization of arginine by Klebsiella aerogenes.

Klebsiella aerogenes utilized arginine as the sole source of carbon or nitrogen for growth. Arginine was degraded to 2-ketoglutarate and not to succinate, since a citrate synthaseless mutant grows on arginine as the only nitrogen source. When glucose was the energy source, all four nitrogen atoms of arginine were utilized. Three of them apparently did not pass through ammonia but were transferred by transamination, since a mutant unable to produce glutamate by glutamate synthase or glutamate dehydrogenase utilized three of four nitrogen atoms of arginine. Urea was not involved as intermediate, since a unreaseless mutant did not accumulate urea and grew on arginine as efficiently as the wild-type strain. Ornithine appeared to be an intermediate, because cells grown either on glucose and arginine or arginine alone could convert arginine in the presence of hydroxylamine to ornithine. This indicates that an amidinotransferase is the initiating enzyme of arginine breakdown. In addition, the cells contained a transaminase specific for ornithine. In contrast to the hydroxylamine-dependent reaction, this activity could be demonstrated in extracts. The arginine-utilizing system (aut) is apparently controlled like the enzymes responsible for the degradation of histidine (hut) through induction, catabolite repression, and activation by glutamine synthetase.     

L-arginine supplementation increases cardiac collagenogenesis in mice chronically infected with Berenice-78 Trypanosoma cruzi strain

Chagas disease, caused by Trypanosoma cruzi, is a major neglected tropical disease that occurs mainly as chronic infection and systemic infection. Currently, there is no suitable and effective drug to treat this parasitic disease. Administration of nutrients with immunomodulatory properties, such as arginine and nitric oxide radicals, may be helpful as antiparasitic therapy. In this study, we evaluated the effects of arginine supplementation during the acute phase of infection under the development of chronic Chagas' heart disease in Swiss mice inoculated with the Berenice-78 strain of T. cruzi. The effectiveness of arginine was determined by daily detection of the parasite in the blood and long-term serum levels of nitric oxide and tumor necrosis factor-alpha, in addition to evaluation of heart tissue damage. Arginine could flatten parasitemia and prevent elevation of tumor necrosis factor-alpha in T. cruzi-infected mice. Regarding chronic inflammatory myocardial derangements, similar findings were verified among T. cruzi-infected groups. Arginine promoted collagenogenesis in the heart muscle tissue of T. cruzi-infected arginine-supplemented group. These data show the paradoxical benefits of arginine in improving the outcome of Chagas chronic cardiomyopathy.