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PubMed1975

Action of (1-des(aspartic acid), 8-isoleucine) angiotensin II upon the pressor and steroidogenic activity of angiotensin II.

The vascular and steroidogenic responses to (1-Sarcosine, 8-Isoleucine)-, and to (1-Des (Aspartic acid), 8-Isoleucine) angiotensin II were compared in bilaterally nephrectomized, ACTH-suppressed dogs receiving constant infusions of angiotensin II. Aldosterone secretion rate was significantly inhibited by pretreatment with 200 ng/Kg/min of the heptapeptide, (1-Des(Aspartic acid), 8-Isoleucine) ang II, but not by similar doses of the octapeptide, (1-Sarcosine, 8-Isoleucine) ang II. In contrast, the pressor action of ang II was unaffected by (1-Des (Aspartic acid), 8-Isoleucine) ang II though significant inhibition occurred with relatively small doses of (1-Sarcosine, 8-Isoleucine) ang II. This study suggests that: (a) angiotensin receptors in adrenal cortex and vascular smooth muscle are functionally different, and (b) (1-Des(Aspartic acid),8-Isoleucine) angiotensin II is a specific antagonist of steroidogenic effect of ang II.

Adrenal Cortex↗
PubMed1999

Influence of postruminal supplementation of methionine and lysine, isoleucine, or all three amino acids on intake and chewing behavior, ruminal fermentation, and milk and milk component production.

Four multiparous Holstein cows were fed a basal diet balanced with the Cornell Net Protein and Carbohydrate System (CNCPS). Diets were formulated to be co-limiting in intestinally absorbable supplies of methionine, lysine, and isoleucine. Cows were supplemented with no amino acids (control); lysine and methionine in a ruminally protected form; isoleucine by abomasal infusion; or lysine, methionine, and isoleucine in a 4x4 Latin square arrangement of treatments with 28-d periods. Performance of cows on all treatments was lower than expected due to low intake of DM that could have been caused by the high fiber level of the basal diet. This high fiber level was likely responsible for the high daily chewing times for cows fed all diets, which was consistent with the high ruminal pH values. Intake of DM and its components were not influenced by any treatment. Milk protein percentage tended to be higher when cows were fed diets supplemented with ruminally protected lysine and methionine; however, production of milk, milk fat, and milk lactose were not affected by any treatment. Cows tended to have a higher milk lactose proportion and tended to produce more milk and milk lactose when they were abomasally infused with isoleucine alone. However, when cows were supplemented with all three amino acids, milk production and composition did not differ from that of cows fed the unsupplemented diet. Use of the CNCPS to evaluate the performance of the cows fed the unsupplemented diet suggested that these cows may have been colimited by intestinally absorbable supplies of lysine, isoleucine, and methionine in addition to metabolizable protein. Evaluation of the unsupplemented diet with an alternate model, Shield, suggested that cows fed the unsupplemented diet may have been colimited by intestinally absorbable supplies of lysine, isoleucine, and arginine. Results suggest that enhanced delivery of intestinally absorbable isoleucine may stimulate milk lactose synthesis.

Animal Feed↗
PubMed1995

Use of Feedback-Resistant Threonine Dehydratases of Corynebacterium glutamicum To Increase Carbon Flux towards l-Isoleucine.

The biosynthesis of l-isoleucine proceeds via a highly regulated reaction sequence connected with l-lysine and l-threonine synthesis. Using defined genetic Corynebacterium glutamicum strains characterized by different fluxes through the homoserine dehydrogenase reaction, we analyzed the influence of four different ilvA alleles (encoding threonine dehydratase) in vectors with two different copy numbers on the total flux towards l-isoleucine. For this purpose, 18 different strains were constructed and analyzed. The result was that unlike ilvA in vectors with low copy numbers, ilvA in high-copy-number vectors increased the final l-isoleucine yield by about 20%. An additional 40% increase in l-isoleucine yield was obtained by the use of ilvA alleles encoding feedback-resistant threonine dehydratases. The strain with the highest yield was characterized by three hom(Fbr) copies encoding feedback-resistant homoserine dehydrogenase and ilvA(Fbr) encoding feedback-resistant threonine dehydratase on a multicopy plasmid. It accumulated 96 mM l-isoleucine, without any l-threonine as a by-product. The highest specific productivity was 0.052 g of l-isoleucine per g of biomass per h. This comparative flux analysis of isogenic strains showed that high levels of l-isoleucine formation from glucose can be achieved by the appropriate balance of homoserine dehydrogenase and threonine dehydratase activities in a strain background with feedback-resistant aspartate kinase. However, still-unknown limitations are present within the entire reaction sequence.

Journal Article↗
PubMed1984

Effect of peptide histidine isoleucine on water and electrolyte transport in the human jejunum.

Peptide histidine isoleucine, a 27 amino acid peptide with close amino acid sequence homology to vasoactive intestinal peptide and secretin, is distributed throughout the mammalian intestinal tract, where it has been localised to intramural neurones. An intestinal perfusion technique has been used to study the effect of intravenous peptide histidine isoleucine (44.5 pmol/kg/min) on water and electrolyte transport from a plasma like electrolyte solution in human jejunum in vivo. Peptide histidine isoleucine infusion produced peak plasma peptide histidine isoleucine concentrations in the range 2000-3000 pmol/l, flushing, tachycardia and a reduction in diastolic blood pressure. Peptide histidine isoleucine caused a significant inhibition of net absorption of water, sodium, potassium and bicarbonate and induced a net secretion of chloride, these changes being completely reversed during the post-peptide histidine isoleucine period. These findings suggest that endogenous peptide histidine isoleucine may participate in the neurohumoral regulation of water and electrolyte transport in the human jejunum.

Adult↗
PubMed1964

VALINE-ISOLEUCINE METABOLISM IN ACETOBACTER SUBOXYDANS AND THE INHIBITION OF GROWTH BY VALINE.

Kerwar, Suresh S. (Oregon State University, Corvallis), Vernon, H. Cheldelin, and L. W. Parks. Valine-isoleucine metabolism in Acetobacter suboxydans and the inhibition of growth by valine. J. Bacteriol. 88:179-186. 1964.-Extracts of Acetobacter suboxydans can synthesize valine and isoleucine via acetolactate and acetohydroxybutyrate, respectively. The amounts of these amino acids synthesized from different intermediates were determined. The pathways appear to be identical to those described for yeast, Neurospora, and Escherichia coli. When exogenous valine was added to a synthetic growth medium inoculated with A. suboxydans, no growth of the culture was observed. The inhibitory effect of valine was reversed by the addition of isoleucine. The site and mechanism of valine inhibition were investigated. Threonine deaminase was inhibited by valine and isoleucine but not by leucine. Repression of the deaminase by isoleucine but not by valine was indicated. The data reported in this paper suggest that valine prevented growth of the organism through false feedback inhibition of threonine deaminase, thereby limiting isoleucine biosynthesis.

Acetobacter↗
PubMed1978

The role of enoyl-coa hydratase in the metabolism of isoleucine by Pseudomonas putida.

The purpose of the present study was to determine if the enoyl coenzyme A hydratase formed by Pseudomonas putida during growth on isoleucine was a unique enzyme specific for isoleucine metabolism. The highest levels of the hydratase were formed during growth on isoleucine intermediates and the lowest levels during growth on glutamate and glucose. Data from growth experiments revealed that 2-methyl-3-hydroxybutyryl coenzyme A hydratase, an enzyme unique to isoleucine metabolism and enoyl coenzyme A hydratase were coordinately induced, but that 3-hydroxyacyl coenzyme A dehydrogenase was under separate control. The hydratase was purified 180-fold from isoleucine cells, and its physical and catalytic properties reported. The highest activity was with crotonyl coenzyme A,Vmax = 1100 x 10(3) moles/min mole enzyme, next was tiglyl coenzyme A, Vmax = 61 x 10(3) moles/min mole enzyme, and last was 3-methyl-crotonyl coenzyme A, Vmax = 2.3 x 10(3) moles/min mole enzyme. Enzyme purified from butyrate cells had the same elution patterns during column chromatography and catalytic properties as the enzyme from isoleucine cells. These data support the conclusion that a single enzyme in P. putida is responsible for the hydration of both tiglyl coenzyme A and crotonyl coenzyme A.

Butyrates↗
PubMed2001

Metabolic redirection of carbon flow toward isoleucine by expressing a catabolic threonine dehydratase in a threonine-overproducing Corynebacterium glutamicum.

Carbon destined for lysine synthesis in Corynebacterium glutamicum ATCC 21799 can be diverted toward threonine by overexpression of genes encoding a feedback-insensitive homoserine dehydrogenase (hom(dr)) and homoserine kinase (thrB). We studied the effects of introducing two different threonine dehydratase genes into this threonine-producing system to gauge their effects on isoleucine production. Co-expression of hom(dr), thrB, and ilvA, which encodes a native threonine dehydratase, caused isoleucine to accumulate to a final concentration of 2.2+/-0.2 g l(-1), five-fold more than accumulates in the wild-type strain, and approximately twice as much as accumulates in the strain expressing only hom(dr) and thrB. Comparing these data with previous results, we found that overexpression of the three genes, hom(dr), thrB, and ilvA, in C. glutamicum ATCC 21799 is no better in terms of isoleucine production than the expression of a single gene, tdcB, encoding a catabolic threonine dehydratase from Escherichia coli. Co-expression of hom(dr), thrB, and tdcB, however, caused the concentration of isoleucine to increase 20-fold compared to the wild-type strain, about four times more than the corresponding ilvA-expressing strain. In this system, the apparent yield of isoleucine production was multiplied by a factor of two [2.1 mmol (g dry cell weight)(-1)]. While the balance of excreted metabolites showed that the carbon flow in this strain was completely redirected from the lysine pathway into the isoleucine pathway, it also showed that more pyruvate was diverted into amino acid synthesis.

Base Sequence↗
PubMed1976

The existence of three types of acetohydroxy acid synthetase in an isoleucine-requiring mutant of Aerobacter aerogenes.

The synthesis of the three types of acetolactate synthase (EC 4.1.3.18) which are responsible for the biosynthesis os isoleucine and valine, was observed in Aerobacter aerogenes I-12, an isoleucine-requiring mutant, when grown on the four kinds of media. When the cells were grown on isoleucine-rich medium, acetolactate synthase sensitive to feedback inhibition and having an optimum pH at 8.0 was formed. By increasing the amount of potassium phosphate in the medium, the catabolite repression of the enzyme having an optimum pH at 6.0 and which is insensitive to feedback inhibition, was released. In contrast, acetolactate synthase having an optimum pH at 8.0 and insensitive to feedback inhibition was formd when isoleucine was limited, irrespective of phosphate concentrations. Two insensitive enzymes were not regulated by isoleucine, leucine and valine, although sensitive pH 8.0 enzyme was repressed by them. Thus, it may be assumed that the synthesis of insensitive pH 8.0 enzyme were repressed by limiting the amount of isoleucine is still open.

Acetolactate Synthase↗
PubMed1985

The different effects of leucine, isoleucine, and valine on systolic properties of the normal and septic isolated rat heart.

Protein turnover in cardiac and skeletal muscle is affected by the provision of amino acids, particularly the branched chain amino acids (BCAA). The effect of each of the BCAA, valine, leucine, and isoleucine, on the systolic function of isolated normal or septic rat heart perfused as a Langendorff preparation was examined. Thirty normal control and 28 septic rats (cecal ligation and puncture) were perfused with either Krebs + 8.5 mM glucose or Krebs + 5.0 mM glucose and 3.5 mM valine, leucine, or isoleucine. Septic hearts perfused with Krebs + 8.5 mM glucose exhibited developed force (DF) and force velocity (dF/dt) levels which were reduced to an average of 45 and 50%, respectively, compared to normal controls, and improved by 35% during 60 min perfusion over measurements made at time zero. In normal hearts DF and dF/dt decreased significantly during perfusion with leucine (27%) and isoleucine (20%). In sepsis, perfusion with leucine and isoleucine resulted in a mild improvement in systolic function. However, valine was far less effective than leucine and isoleucine in maintaining systolic function in sepsis, due apparently to valine being a less efficient energy substrate for the cardiac muscle in a state of severe energy deficit. Thus, valine, leucine, and isoleucine seem to exert different effects on the systolic function of normal and septic isolated rat hearts.

Amino Acids, Branched-Chain↗
PubMed1995

A comparative catabolism study of isoleucine by insect and mammalian tissues.

The metabolism of [U-14C]isoleucine was examined in different tissues of five species of lepidopteran and four species of non-lepidopteran insects. Slices of fat body, epidermis, Malpighian tubule, gut, and muscle were incubated in a culture medium containing [U-14C]isoleucine; the medium was analyzed by ion-exclusion LC to quantify labeled metabolites. Tissues of lepidopteran insects secrete high levels of metabolites including 2-keto-4-methylvalerate, 2-methylbutyrate, propionate, and acetate. Tissues of non-lepidopteran insects secrete low amounts of these acids. Analysis of isoleucine transaminase activity in selected tissues of non-lepidopteran insects indicated that those tested contain significant activity. These results demonstrate that tissues of lepidopteran insects have a unique ability to secrete short chain acids, derived from isoleucine, into the medium. The secretion of propionate correlates with the ability to synthesize ethyl-branched juvenile hormones and indicates the presence of an efficient transport system for short chain acids. We also monitored the secretion of acidic metabolites of isoleucine by different tissues of the rat. Muscle was most active in secreting keto acid whereas heart secreted high levels of 2-methylbutyrate. Negligible quantities of metabolites of isoleucine were secreted by the liver.

Animals↗
PubMedDate not supplied

[Absorption and utilization of amino acids infused into the cecum of growing swine. 3. Studies with 15N- and 14C-labeled isoleucine].

In 3 experiments growing female pigs, (live weight 35-56 kg) received continuous infusions of 15N-labelled or 15N- and 14C-doubly labelled isoleucine by means of caecal cannulae. The whereabouts of the infused isoleucine were investigated. Between 8.9 and 12.3% of the infused 15N-excess (15N') was excreted in faeces mainly in the forms of bacteria protein, between 0.7 and 0.9% only of the infused amount unchanged as 15N-isoleucine. The highest quota is microbially decomposed in the colon and absorbed in the form of NH3 or amines. Between 45 and 70% of the infused 15N are excreted in urine, mainly as urea (85-95% of the 15N-amount in urine). Virtually no 15N from the infused isoleucine is incorporated in the organ and tissue proteins (exception: colon wall). These findings are corroborated by the 14C-activity measuring as no intact 14C labelled isoleucine could be detected in the tissue protein. These results show that intact isoleucine is not absorbed in the colon. The nitrogen originating from the absorbed NH3 is nearly completely excreted in urine and thus not available to the biosynthesis of body protein.

Animals↗
PubMed1980

Leucine, isoleucine, valine and histidine requirements of fingerling channel catfish.

Growth studies were conducted with fingerling channel catfish to determine the minimal requirements for the amino acids leucine, isoleucine, valine and histidine. The experimental diets were formulated from purified ingredients to contain 24% crude protein and 275 kcal/100 g diet. Casein and gelatin served as protein sources and were supplemented with crystalline L-amino acids to provide the amino acid pattern found in 24% crude protein from whole egg powder. Based on dry diet the catfish required 0.84 +/- 0.04% leucine, 0.62 +/- 0.04% isoleucine, 0.71 +/- 0.03% valine and 0.37 +/- 0.01% histidine. These values correspond to 3.50% leucine, 2.58% isoleucine 2.96% valine and 1.54% histidine when expressed as a percentage of dietary protein. Quantitation of serum free amino acid levels revealed a marked increase in valine and isoleucine in leucine-deficient fish. In addition, increases in dietary isoleucine or valine resulted in changes in the serum levels of isoleucine, valine and leucine. These data indicate an apparent interaction among these amino acids in the catfish comparable to that previously observed in other species. Dietary histidine caused no increase in serum free histidine levels until the dietary requirement was reached. Muscle carnosine could not be detected in the catfish.

Amino Acids, Essential↗
PubMed1985

Kinetic analysis of cerebrovascular isoleucine transport from saline and plasma.

The concentration dependence of regional isoleucine transport across the blood-brain barrier was determined in anesthetized rats with the in situ brain perfusion technique of Takasato et al. [Am. J. Physiol. 247, H484-493 (1984)]. This technique allows, for the first time, accurate measurements of cerebrovascular amino acid transport in the absence of competing amino acids using saline perfusate, and in the presence of physiological concentrations of amino acids using plasma perfusate. Cerebrovascular isoleucine transport from saline perfusate followed Michaelis-Menten saturation kinetics where Vmax = 9 - 11 X 10(-4) mumol X s-1 X g-1 and Km = 0.054-0.068 mumol X ml-1 in six brain regions. A component of nonsaturable transport was not detected in any brain region even though perfusate isoleucine concentration was increased to greater than or equal to 150 times the normal plasma concentration. Isoleucine influx during plasma perfusion was only 8% of that predicted from the saline perfusion data due to transport inhibition by competing amino acids in plasma. Competitive inhibition increased the apparent Km for isoleucine transport from plasma by greater than or equal to 24-fold to 1.5-1.7 mumol X ml-1. These data provide accurate new estimates of the kinetic constants that describe amino acid transport across the blood-brain barrier. In addition, they indicate that the cerebrovascular transfer-site affinity (1/Km) for isoleucine is approximately fivefold greater than previously reported with the brain uptake index technique.

Animals↗
PubMed1965

Use of the stereoisomers of isoleucine by Lactobacillus fermenti.

The use of four stereoisomers of isoleucine by Lactobacillus fermenti strain 36 was studied in detail. All four isoleucine isomers were used for growth in the presence of vitamin B(6) compounds, but only l-isoleucine was active in the absence of these vitamins. Of the vitamin B(6) compounds, pyridoxal and pyridoxamine were equally more effective than pyridoxine for the utilization of these isomers. Lowering the initial pH, decreasing the amounts of leucine and valine, and adapting the organism to d-alloisoleucine medium accelerated the use of isoleucine isomers. Thus, the conditions were established under which respective isomers gave the same growth response, and these findings were applied to the separate microbiological assay of l-isoleucine and total isoleucine isomers.

Biological Assay↗
PubMed1971

Increase in isoleucine accumulation by alpha-aminobutyric acid-resistant mutants of Serratia marcescens.

Several alpha-aminobutyric acid-resistant (Abu-r) mutants of Serratia marcescens were found to be superior to the parent strain in converting d-threonine to l-isoleucine. One of them accumulated 1.5 times more l-isoleucine that the parent strain. The level of acetohydroxy acid (AHA) synthetase in this mutant increased twofold above that of the parent strain. In the parent strain, AHA synthetase was repressed and l-isoleucine accumulation was decreased by either l-valine or l-leucine, whereas in the mutant the AHA synthetase level and l-isoleucine accumulation were not affected by these amino acids. AHA synthetase of the Abu-r mutant was feedback-inhibited by l-valine to the same extent as that of the parent strain. The level of d-threonine dehydratase in both strains was only slightly affected by several amino acids tested. l-Threonine dehydratase of the parent strain and of the mutant was almost completely inhibited by l-isoleucine. These results indicate that the increase in l-isoleucine accumulation by Abu-r mutants is due to the genetic derepression of AHA synthetase.

Aminobutyrates↗
PubMed1975

Competition between Chlamydia psittaci and L cells for host isoleucine pools: a limiting factor in chlamydial multiplication.

L cells (mouse fibroblasts) supported the multiplication of the obligately intracellular parasitic bacterium Chlamydia psittaci (strain 6BC) when incubated in fresh growth medium (medium 199 + 5% fetal calf serum). When incubated in the medium supernatant from a 24-h-old culture of uninfected L cells (24-h used medium), uninfected cells did not divide and infected cells did not provide an adequate environment for the multiplication of C. psittaci, which persisted in a noninfectious latent state within the host cells. The failure of both L cells and chlamydiae to divide resulted from an overall reduction in the rate of protein synthesis by both host and parasite brought about by an insufficiency of the essential amino acid isoleucine in 24-h used medium. The concentration of isoleucine required to activate minimal growth of C. psittaci also minimally stimulated uninfected L cells to divide. The addition of cycloheximide to 24-h used medium also activated the latent chlamydial infection because it stimulated the incorporation of host protein-derived isoleucine into chlamydial protein. The results suggest that the chlamydial parasite and the L-cell host compete for the isoleucine in the soluble pool of the host cell and that the parasite is capable of sequestering isoleucine for its own biosynthetic needs only when the concentration of isoleucine in the host pool rises above the level required to maintain the hose in the stationary state. Extrapolation of the results obtained with the L cell-C. psittaci model system to natural latent chlamydial infections is discussed.

Animals↗
PubMed1974

D- and L-isoleucine metabolism and regulation of their pathways in Pseudomonas putida.

Pseudomonas putida oxidized isoleucine to acetyl-coenzyme A (CoA) and propionyl-CoA by a pathway which involved deamination of d-isoleucine by oxidation and l-isoleucine by transamination, oxidative decarboxylation, and beta oxidation at the ethyl side chain. At least three separate inductive events were required to form all of the enzymes of the pathway: d-amino acid dehydrogenase was induced during growth in the presence of d-isoleucine; branched-chain keto dehydrogenase was induced during growth on 2-keto-3-methylvalerate and enzymes specific for isoleucine metabolism; tiglyl-CoA hydrase and 2-methyl-3-hydroxybutyryl-CoA dehydrogenase were induced by growth on isoleucine, 2-keto-3-methylvalerate, 2-methylbutyrate, or tiglate. Tiglyl-CoA hydrase and 2-methyl-3-hydroxybutyryl-CoA dehydrogenase were purified simultaneously by several enzyme concentration procedures, but were separated by isoelectric focusing. Isoelectric points, pH optima, substrate specificity, and requirements for enzyme action were determined for both enzymes. Evidence was obtained that the dehydrogenase catalyzed the oxidation of 2-methyl-3-hydroxybutyryl-CoA to 2-methylacetoacetyl-CoA. 2-Methyl-3-hydroxybutyryl-CoA dehydrogenase catalyzed the oxidation of 3-hydroxybutyryl-CoA, but l-3-hydroxyacyl-CoA dehydrogenase from pig heart did not catalyze the oxidation of 2-methyl-3-hydroxybutyryl-CoA; therefore, they appeared to be different dehydrogenases. Furthermore, growth on tiglate resulted in the induction of tiglyl-CoA hydrase and 2-methyl-3-hydroxybutyryl-CoA dehydrogenase, but these two enzymes were not induced during growth on crotonate or 3-hydroxybutyrate.

Alcohol Oxidoreductases↗
PubMed1983

Multiple pathways for isoleucine biosynthesis in the spirochete Leptospira.

Spirochetes of the genus Leptospira have previously been shown to use an unusual pathway to synthesize isoleucine. For reasons of convenience, we assume that only one unusual pathway is found in the genus, and we refer to it as the pyruvate pathway. We determined the distribution of this pyruvate pathway in representatives of the seven Leptospira DNA hybridization groups. Our method included labeling the representative strains with radioactive carbon dioxide and other radioactive precursors, fractionating the cells, and determining the specific activities (counts detected per nanomole) of the amino acids found in the protein fractions. On the basis of isoleucine biosynthesis, we found that the genus can be classified as follows: class I primarily, if not exclusively, uses the well-known threonine pathway; class II uses mostly the pyruvate pathway, with a minor amount of isoleucine being synthesized via the threonine pathway; and class III uses the pyruvate pathway exclusively. No relationship appears to exist between the degree of DNA hybridization and the classes of isoleucine biosynthesis. Although the precise intermediates on the pyruvate pathway are unknown, the origin of the carbon skeleton of isoleucine synthesized by this pathway is consistent with a borrowing of the leucine biosynthetic enzymes. However, we found that the pyruvate pathway is not controlled by leucine and that the two isoleucine pathways are independently regulated. Finding major and highly evolved multiple biosynthetic pathways of a specific amino acid within one genus is unique, and, conceivably, represents phylogenetic diversity within Leptospira.

Isoleucine↗