Lysine Oxidation Research Articles

Effect of leucine on amino acid and glucose metabolism in humans

Leucine has been reported to be an important regulator of protein metabolism. We investigated the effect of intravenous infusion of l-leucine versus saline on amino acid metabolism in eight healthy human subjects. Plasma concentrations of amino acids were measured and protein turnover was estimated using l-(1- 13C)lysine and l-(3,3,3- 2H 3)leucine as tracers. Glucose kinetics were measured using d-(6,6- 2H 2)glucose as a tracer. Leucine infusion increased the plasma leucine concentration from 103 ± 8 to 377 ± 35 μmol/L ( P < .01). Plasma concentrations of essential amino acids, including threonine, methionine, isoleucine, valine, tyrosine, and phenylalanine were significantly decreased by leucine infusion. Leucine infusion did not change lysine flux significantly (108 ± 4 during saline v 101 ± 4 μmol/kg/h −1 during leucine infusion), but decreased lysine oxidation (13.2 ± 0.9 v 10.7 ± 1 μmol/kg/h, P < .05) and endogenous leucine flux (from 128 ± 4 to 113 ± 7 μmol/kg/h, P < .05) when plasma ( 2H 3) ketoisocaproate (KIC) was used for calculation. During leucine infusion, the ( 2H 3) KIC to ( 2H 3) leucine plasma enrichment ratio increased from 0.76 ± 0.02 to 0.88 ± 0.01 ( P < .001), while estimation of leucine flux using plasma ( 2H 3) leucine showed no change in endogenous leucine flux. Leucine infusion decreased hepatic glucose production and metabolic clearance of glucose, but did not change plasma concentrations of glucose, insulin, C-peptide, glucagon, epinephrine, norepinephrine, or free fatty acids. We conclude that leucine spares glucose and lysine catabolism and decreases plasma concentrations of essential amino acids. This study also demonstrated that the ratio of plasma KIC enrichment to leucine enrichment does not remain constant in all study conditions.

Lysine oxidation by rat hepatocytes: effect of serum from pigs given a high or low lysine diet

Lysine oxidation by rat hepatocytes: effect of serum from pigs given a high or low lysine diet

Methodologic studies on the metabolically-oriented determination of lysine requirements in broiler chickens. 2. Effect of the lysine content of the diet on the lysine oxidation rate in a 15-hour feed withdrawal before 14C-lysine injection

This experiment was designed to narrow the estimated range for lysine requirement of broiler chickens determined by isotopic techniques. In addition the influence of a long-term feed withdrawal previous 14C-lysine-injection on the lysine catabolism was investigated. 120 male broiler chickens 7 to 21 days posthatching received a diet based on wheat and wheat gluten. Lysine content was varied from 8.3 to 16.0 g/kg DM (3.2 to 6.3 g/16 g N) at 8 levels by supplementing the basal diet with L-lysine-HCl. After the feeding period animals of each group were labelled with 14C-L-lysine by intravenous injection 5.5 and 15.5 hours after feed withdrawal, respectively. During the following 4 hours the excretion of 14CO2 and CO2 was measured. Highest body weight gain was observed in the group with 13.8 g lysine/kg DM. In case of 14CO2 excretion measurements starting 5.5 hours after feed withdrawal an increase of 14CO2 excretion was observed if the lysine content of the diet exceeded 11.6 g/kg DM. This estimated range for lysine requirement (11.6 to 12.7 g/kg DM with 26% CP in the DM) was lower compared with the lysine requirement estimated by the growth curve (12.7 to 13.8 g/kg DM). This discrepancy could be explained by the fact that the results of the metabolism oriented determination of lysine requirement represent the requirement at the actual age, while the feeding experiment reflects a mean lysine requirement of the previous period of 14 days. If the animals were labelled with 14C-lysine 15.5 hours after feed withdrawal no clear response in 14CO2 excretion and specific radioactivity of CO2 on the dietary lysine content was observed.

Lysine kinetics at graded lysine intakes in young men

Healthy young men participated in a study designed to explore the effects of decreasing dietary lysine content on plasma amino acid concentrations and lysine kinetics, studied with L-[113C]lysine as tracer. Diets provided adequate energy and the equivalent (N × 6.25) of 0.8 g protein kg−1·day−1 as a synthetic L-amino acid mixture simulating egg protein. Lysine intake was reduced every 7 days. Changes in plasma amino acids suggested that effects characteristic of a dietary lysine inadequacy were prevented by consuming more than 32 mg lysine·kg−1 day−1. Primed, continuous intravenous infusions of L-[1-13C]lysine, at the end of each diet period while subjects were in the fed state, showed that as dietary lysine was reduced, 13C enrichment increased in plasma lysine and decreased in expired CO2. It was estimated that lysine oxidation exceeded, by 4.4 mg kg−1 day−1, the lysine intake of 20 mg kg−1·day−1 indicating that the lysine required for body protein maintenance would probably exceed this latter value. These results are discussed in relation to the physiological requirement in adults for lysine, currently accepted to be met by an intake of 12 mg kg−1·day−1, which is assumed to be the upper range of the lysine requirement for this population group.

Lysine and protein metabolism in young women. Subdivision based on the novel use of multiple stable isotopic labels.

A multitracer stable isotope study of lysine kinetics was carried out in fasted adult female volunteers to determine whether a multicompartmental model that partitions protein synthesis and breakdown into at least two types of tissue components can be constructed from plasma and breath data. Five female subjects, maintained on formula diets, received L-[13C1]lysine (27 mumol/kg) as an i.v. bolus and L-[15N2]lysine (27 mumol/kg) as an oral bolus 4 h postprandially. Plasma and breath samples were collected for 6 h. On an alternate day, subjects received NaH13CO3 (10 mumol/kg) as an i.v. bolus and breath samples were collected for 6 h. Plasma tracer lysine levels were determined by gas chromatography-mass spectrometry isotope ratiometry, and breath 13CO2 levels were measured by mass spectrometric gas isotope ratiometry. The tracer data could be fitted to a mammillary multicompartmental model that consisted of a lysine central compartment and slow- and fast-exchanging peripheral compartments containing 37, 38, and 324 mumol/kg, respectively. The rates of lysine oxidation, incorporation into protein, and release by protein breakdown were 21, 35, and 56 mmol/kg/h, respectively, in the fast-exchanging compartment, whereas the rates of protein synthesis and breakdown in the slow compartment were both 53 mmol/kg/min. These values corresponded to a whole-body lysine flux of 106 mmol/kg/h. The kinetic parameters were in excellent agreement with reported values obtained by constant-infusion methods. The measurements indicated that it will be possible to detect changes in amino acid pool sizes and protein synthesis and breakdown associated with the mobilization of protein stores from plasma and breath measurements in multitracer stable isotope experiments.

Effect of dietary and extracellular potassium on lysine metabolism in the rat

Previous studies have shown that potassium (K) depletion leads to the accumulation of lysine and other cationic amino acids in tissues. The metabolic nature of this interaction is unknown but is presumably related in part to a unique aspect of these amino acids, possibly their charge. These studies were completed to evaluate the nature of the effect of K on lysine metabolism in the rat. In the first study, 42 rats were maintained on K-deficient or K-adequate diets for 10 days, after which blood and tissue samples were taken from 12 rats for electrolyte, amino acid and blood gas analyses. Tissue slices of liver, kidney and segments of diaphragm were prepared from the remaining 30 rats (15 per group) and incubated in medium containing either 3 or 6 mM K, and effects of dietary and medium K concentrations on lysine catabolism were determined. In the second study, the effects of 0, 3, 6 or 12 mM K on 14C-lysine uptake, catabolism and incorporation into protein were evaluated. Dietary K deficiency did not influence blood pH, bicarbonate concentration or base excess of blood; however, it decreased the concentration of plasma K and caused accumulation of lysine and arginine in muscle and lysine in liver. K deficiency resulted in a 36% reduction in the rate of lysine catabolism in kidney. Much of the dietary K effect may be related to diminished plasma K concentration, as low K concentration in vitro caused similar, although less dramatic, decreases in lysine oxidation, diminished incorporation of lysine into protein in kidney and increased lysine uptake in both liver and kidney. K deficiency appears to conserve lysine in the free form in the intracellular pool by enhancing cellular uptake and by decreasing the degradation of lysine and the utilization of lysine in protein synthesis.

Tryptophan Requirement of the 2.5-kg Piglet Determined by the Oxidation of an Indicator Amino Acid

The tryptophan requirement of 2.5-kg piglets was measured by the oxidation of L-[1-14C]phenylalanine or DL-[1-14C]lysine when meals containing various levels of L-tryptophan were offered. Increasing dietary tryptophan from 0.65 to 2.0 g/kg decreased 14CO2 release from L-[1-14C]phenylalanine but further increases in dietary tryptophan level resulted in no further decrease in 14CO2 output. Regression analysis, with a crossover model, showed phenylalanine oxidation was minimized with a dietary tryptophan level of 1.94 g/kg (95% confidence limits 1.93 to 1.95). The oxidation of lysine was also reduced by increasing tryptophan levels to 2 g/kg; as tryptophan level was increased to 3 g/kg there was no statistically significant reduction of lysine oxidation. These studies suggest that the dietary tryptophan requirement of the 2.5-kg piglet is no more than 2 g/kg of a 240 g protein per kilogram diet.

Adaptive responses of liver and kidney lysine-ketoglutarate reductase and lysine oxidation in rats fed graded levels of dietary lysine and casein.

The effects of dietary lysine and protein levels on liver and kidney lysine-ketoglutarate reductase (LKGR) activities and on the oxidation of lysine to expired C02 were studied in weanling rats. Liver LKGR activity in rats fed 20% wheat gluten diets supplemented with 1.0 and 5.0% lysine HC1 reached a maximum at 7 to 10 days. At levels below 0.5% lysine HC1 supplementation, liver LKGR maintained a low activity, but above this intake level, the activity increased linearly with increased lysine. Liver LKGR activity also increased with graded levels of dietary casein. A similar response to dietary lysine and casein levels was observed in kidney LKGR, but was a lesser degree. The oxidation of lysine to expired C02 after intraperitoneal injection of L-lysine-U-14C was greatly elevated as dietary lysine or casein levels increased, and the response pattern was quite similar to that of the liver LKGR activity. Results with wheat gluten suggest that the estimaion of liver LKGR activity as well as the lysine oxidati...

CROTONASE DEFICIENCY: DEMONSTRATION OF A DEFECT IN β-OXIDATION IN MAN

A patient who presented with severe acidosis (CO2, 4 meq/L) without hypoglycemia was found to have 1 mM crotonic acid in his serum. During an elective 20 hr fast, β-OH butyrate and aceto-acetate rose to 5.3 mM and 1.9 mM, Serum alanine and glucose fell to 137 μM and 57 mg/dl. Crotonic acid rose from undetectable levels to 160 μ M at 20 hrs but continued to rise after the fast was terminated to 700 μ M by 34 hrs. β-OH butyric acid is not converted to crotonic acid by the methods used. The elevation of crotonic acid appears highly specific as no crotonic acid could be demonstrated in other severely acidotic patients (diabetes, propionic acidemia, ketotic hypoglycemia). Metabolic studies were carried out in isolated leukocytes. Total crotonase activity was >3 S.D. below normal (.125 vs .319±.051 OD280/min/mg) o Tiglyl CoA enoyl hydrase, β-OH butyryl CoA de-hydrogenase, and oxidation of branched chain amino acids were normal. Lysine oxidation (which requires crotonase) was 36% of normal. Palmitate oxidation was <25% of age matched controls but only 10-25% reduced from adult controls. Butyrate oxidation was 40% of age matched controls but only slightly reduced from adult values. In fibroblasts butyrate oxidation was 41% of control values. This child exhibits a partial defect in β-oxidation. These studies also suggest that the enoyl hydrases for branch chain amino acid metabolism may be distinct from crotonase.

Studies on methods for the determination of amino acid requirements for metabolic balance based on the oxidation rate of 14C labeled lysine to 14CO2

Male experimental rats (100 gm liveweight) were distributed into 10 groups of 8 animals each and received balanced diets, with the exception of lysine which was added to the diets in graded amounts in such a way that the lysine content of the diets ranged from 2.44 to 5.92 gm/16 gm N. After a feeding period of 7 days the animals received 3H- and 14C lysine injected intraperitoneally, 4 animals of each group were investigated for the total CO2 excretion and 14CO2 excretion during the first 2 hrs after the injection and for the urinary excretion of radioactivity (48 hours). The remaining animals in each group were used for determining the plasma amino acids and for establishing the specific radioactivity of free lysine in the liver and muscles after an 1-hour incorporation period. Total CO2 excretion was not found to be influenced by the lysine contents while the level of excretion of 14C activity through CO2 and that of specific 14C activity of CO2 increased with increasing lysine concentrations. This produced a broken curve pattern, showing an increased release of 14CO2 (under maintenance conditions) if the diet contained 4 gm lysine/16 gm N and more. Investigations for the specific 14C activity of free lysine in the liver, the main site of lysine oxidation, showed that the increase in 14CO2 release was due to an enhanced rate of lysine catabolism and was not brought about by changes in the pool volume or in specific radioactivity. The levels of urinary 14C excretion were not found to be related to the lysine content of the diets, whereas the curve pattern of 3H excretion observed 5 to 8 hrs after injection was similar to that of 14CO2 excretion. The lysine content of blood plasma and the content of free lysine in the liver increased continuously with increasing levels of dietary lysine. The methodological studies made in the present paper showed that in scientific research a determination of amino acid requirements on the basis of CO2 oxidation data may be a very exact and sensitive method. It will also yield values for maintenance requirements.

Control of Ketogenesis from Amino Acids. IV. Tissue Specificity in Oxidation of Leucine, Tyrosine, and Lysine1

In vitro and in vivo studies were made on the tissue specificity of oxidation of the ketogenic amino acids, leucine, tyrosine, and lysine. In in vitro studies the abilities of slices of various tissues of rats to form 14CO2 from 14C-amino acids were examined. With liver, but not kidney slices, addition of alpha-ketoglutarate was required for the maximum activities with these amino acids. Among the various tissues tested, kidney had the highest activity for lysine oxidation, followed by liver; other tissues showed very low activity. Kidney also had the highest activity for leucine oxidation, followed by diaphragm; liver and adipose tissue had lower activities. Liver had the highest activity for tyrosine oxidation, but kidney also showed considerable activity; other tissues had negligible activity. In in vivo studies the blood flow through the liver or kidney was stopped by ligation of the blood vessels. Then labeled amino acids were injected and recovery of radioactivity in respiratory 14CO2 was measured. In contrast to results with slices, no difference was found in the respiratory 14CO2 when the renal blood vessels were or were not ligated. On the contrary ligation of the hepatic vessels suppressed the oxidations of lysine and tyrosine completely and that of leucine partially. Thus in vivo, lysine and tyrosine seem to be metabolized mainly in the liver, whereas leucine is metabolized mostly in extrahepatic tissues and partly in liver. Use of tissue slices seems to be of only limited value in elucidating the metabolisms of these amino acids.

Effect of protein content of diet on lysine oxidation by the rat

Feeding rats a high protein diet increased their ability to oxidize a loading dose of lysine to CO 2 in vivo. The rate of oxidation of lysine to CO 2 by liver homogenates from rats consuming a high protein diet increased with time, reaching a maximum by 10 days.

Associations among food and protein intake, serine dehydratase, and plasma amino acids.

Associations among food and protein intake, serine dehydratase, and plasma amino acids.

Oxidation, utilization, and incorporation into protein of alanine and lysine during metamorphosis of the blowfly Phormia regina (Meigen)

The extent of alanine and lysine oxidation by various developmental stages of the blowfly Phormia regina is stage specific. Both amino acids are most slowly oxidized at about half way along adult development, but alanine is most rapidly oxidized by the adult fly, and lysine by the white pupa at the commencement of pupation. The rate of utilization ( K a ) for free pool alanine is at all corresponding stages higher than for lysine. Variations in K a -alanine during metamorphosis are far more pronounced than for K a -lysine, K a -alanine being particularly high in the white pupa. Alanine and lysine were incorporated into total protein at identical rates ( K p ) during metamorphosis except in the mature fly, where K p -lysine was higher than K p -alanine. The K p values, at all times low, decreased markedly during adult development. It is suggested that protein synthesis during blowfly metamorphosis is less extensive than had previously been assumed.

Animal Behavior and Internal Drives

Animal Behavior and Internal Drives