The dissimilation of leucine, isoleucine and valine to volatile fatty acids by adult Fasciola hepatica

The dissimilation of leucine, isoleucine and valine to volatile fatty acids was determined in Fasciola hepatica and the degradation of (U−¹⁴C) branched amino acids to the volatile fatty acids end products demonstrated. F. hepatica was found to metabolize leucine, isoleucine and valine to isovaleric, 2-methylbutyric and isobutyric acid respectively. The rate of formation of isobutyrate, isovalerate and 2-methylbutyrate was found to be positively related to the rate of propionic acid production with air or nitrogen as the gas phase. However, under 95% O₂/5% CO₂ the formation of the branched chain acids was independent of propionic acid production. The production of isobutyrate, isovalerate and 2-methylbutyrate caused a simultaneous reduction in the rate of acetate formation. The role of propionate formation in regulating metabolism is discussed.     

Interference between leucine, isoleucine and valine during intestinal absorption

1. The reciprocal interference between l-leucine, l-isoleucine and l-valine during absorption was studied in rats both in vivo and with an everted-sac preparation in vitro. 2. After feeding with the amino acids alone there was a considerable increase in their concentration in the intestinal lumen followed by a rapid disappearance, indicating efficient absorption. Absorption was reflected by a high concentration of the respective amino acids in the portal plasma. Isoleucine and valine inhibited the absorption of leucine, and leucine inhibited the absorption of isoleucine and valine. Inhibition of absorption by the interfering amino acid was generally partly overcome after 30–60min., probably through the absorption of the interfering amino acid. At that time the rise in the concentration of the amino acid in portal plasma began. 3. These results were confirmed by experiments in vitro: isoleucine and valine inhibited the absorption rate of leucine, and leucine that of isoleucine and valine. 4. Active absorption of amino acids was rapid at low concentrations and depressed at higher concentrations.     

Volatile acid production from threonine,valine, leucine and isoleucine by clostridia

The amounts of the volatile acids produced from thereonine, valine, leucine and isoleucine by growing cultures of clostridia have been measured. The species used were Clostridium sporogenes; C. caloritolerans; C. botulinum proteolytic type A; C. botulinum proteolytic type B; C. botulinum proteolytic type F; C. botulinum proteolytic type G; C. putrificum; C. difficile; C. ghoni; C. bifermentans; C. sordellii; C. mangenoti; C. cadaveris; C. lituseburense; C. propionicum; C. sticklandii; C. scatologenes; C. subterminale; C. putrefaciens; C. histolyticum; C. tetanomorphum; C. limosum; C. lentoputrescens; C. tetani; C. melanomenatum; C. cochlearium; C. sporospheroides. Most of the species tested gave increased yields of propionic acid when grown in the threonine medium; in addition, some species resembled C. propionicum and produced n-butyric acid when grown in this medium. C. histolyticum produced only acetic acid in the basal medium; all seven strains of this species produced more acetic acid when grown in the threonine medium than in the basal medium. Species which oxidize valine to iso-butyric acid also oxidize leucine to 3-methyl butyric acid and isoleucine to 2-methylbutyric acid. The iso-caproic fraction produced by some species is shown to be derived from leucine. The identitity of the branched-chain acids produced by C. sporogenes has been confirmed by gas liquid chromatography/mass spectrometry.Abbreviations GLC gas liquid chromatography - RCM reinforced clostridial medium - VFA volatile fatty acid     

Interference with valine and isoleucine biosynthesis by cyclic hydroxamic acids

Hogg, Robert W. (University of Illinois, Urbana), Chitra S. Biswas, and Harry P. Broquist. Interference with valine and isoleucine biosynthesis by cyclic hydroxamic acids. J. Bacteriol. 90:1265-1270. 1965.-The introduction of a hydroxyl group in a number of common barbiturates, a substitution which converts these compounds to cyclic hydroxamic acids, gives rise to compounds which inhibit growth of Escherichia coli. The toxicity of these hydroxybarbiturates appears to be associated, at least in part, with interference with valine and isoleucine biosynthesis, as a combination of these amino acids counteracts their toxicity. A subinhibitory level of 1-hydroxy-5-ethyl-5-isopropylbarbituric acid (hydroxyipral) was counteracted either by valine or by its early precursor, alpha-acetolactate, and led to a study of the effect of these cyclic hydroxamic acids on acetolactate synthesis in a cell-free enzyme system of E. coli. In this system, the parent barbiturates and their respective hydroxy derivatives were only moderately active in blocking acetolactate synthesis. Detailed kinetic studies of the most active compound, hydroxyipral showed no obvious relationship to the substrate or cofactors of the system. The inhibitory effects of hydroxyipral, either on growth of E. coli or in the acetolactate-forming system, could not be counteracted by Fe(++), but the toxic effect of aspergillic acid and o-phenanthroline in these instances was reversed by Fe(++), which implies an iron involvement in the acetolactate-forming system of E. coli.     

Symbiotic characterization of isoleucine+valine and leucine auxotrophs of Sinorhizobium meliloti

Ten isoleucine+valine and three leucine auxotrophs of Sinorhizobium meliloti Rmd201 were obtained by random mutagenesis with transposon Tn5 followed by screening of Tn5 derivatives on minimal medium supplemented with modified Holliday pools. Based on intermediate feeding, intermediate accumulation and cross-feeding studies, isoleucine+valine and leucine auxotrophs were designated as ilvB/ilvG, ilvC and ilvD, and leuC/leuD and leuB mutants, respectively. Symbiotic properties of all ilvD mutants with alfalfa plants were similar to those of the parental strain. The ilvB/ilvG and ilvC mutants were Nod-. Inoculation of alfalfa plants with ilvB/ilvG mutant did not result in root hair curling and infection thread formation. The ilvC mutants were capable of curling root hairs but did not induce infection thread formation. All leucine auxotrophs were Nod+ Fix-. Supplementation of leucine to the plant nutrient medium did not restore symbiotic effectiveness to the auxotrophs. Histological studies revealed that the nodules induced by the leucine auxotrophs did not develop fully like those induced by the parental strain. The nodules induced by leuB mutants were structurally more advanced than the leuC/leuD mutant induced nodules. These results indicate that ilvB/ilvG, ilvC and one or two leu genes of S. meliloti may have a role in symbiosis. The position of ilv genes on the chromosomal map of S. meliloti was found to be near ade-15 marker.     

Separate regulation of transport and biosynthesis of leucine, isoleucine, and valine in bacteria.

Since both transport activity and the leucine biosynthetic enzymes are repressed by growth on leucine, the regulation of leucine, isoleucine, and valine biosynthetic enzymes was examined in Escherichia coli K-12 strain EO312, a constitutively derepressed branched-chain amino acid transport mutant, to determine if the transport derepression affected the biosynthetic enzymes. Neither the iluB gene product, acetohydroxy acid synthetase (acetolactate synthetase, EC 4.1.3.18), NOR THE LEUB gene product, 3-isopropylmalate dehydrogenase (2-hydroxy-4-methyl-3-carboxyvalerate-nicotinamide adenine dinucleotide oxido-reductase, EC 1.1.1.85), were significantly affected in their level of derepression or repression compared to the parental strain. A number of strains with alterations in the regulation of the branched-chain amino acid biosynthetic enzymes were examined for the regulation of the shock-sensitive transport system for these amino acids (LIV-I). When transport activity was examined in strains with mutations leading to derepression of the iluB, iluADE, and leuABCD gene clusters, the regulation of the LIV-I transport system was found to be normal. The regulation of transport in an E. coli strain B/r with a deletion of the entire leucine biosynthetic operon was normal, indicating none of the gene products of this operon are required for regulation of transport. Salmonella typhimurium LT2 strain leu-500, a single-site mutation affecting both promotor-like and operator-like function of the leuABCD gene cluster, also had normal regulation of the LIV-I transport system. All of the strains contained leucine-specific transport activity, which was also repressed by growth in media containing leucine, isoleucine and valine. The concentrated shock fluids from these strains grown in minimal medium or with excess leucine, isoleucine, and valine were examined for proteins with leucine-binding activity, and the levels of these proteins were found to be regulated normally. It appears that the branched-chain amino acid transport systems and biosynthetic enzymes in E. coli strains K-12 and B/r and in S. typhimurium strain LT2 are not regulated together by a cis-dominate type of mechanism, although both systems may have components in common.     

The adverse metabolic effects of branched-chain amino acids are mediated by isoleucine and valine

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