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PubMed2000

Pathways for amino acid metabolism by Prevotella intermedia and Prevotella nigrescens.

Pathways for amino acid metabolism by Prevotella intermedia and Prevotella nigrescens were investigated. Prevotella strains grew anaerobically in tryptone-based medium and their growth increased upon the addition of aspartate to the medium. Washed cells of tryptone-grown strains metabolized aspartate to succinate, acetate, fumarate, malate, formate and ammonia, while from tryptone they produced isobutyrate and isovalerate in addition to the end products from aspartate. Cell extracts obtained from the tryptone-grown cells had aspartate ammonia-lyase for the conversion of aspartate to fumarate. Methylviologen-dependent fumarate reductase was found to reduce fumarate to succinate. A series of enzymatic activities, including fumarase, NAD-dependent malate dehydrogenase, oxaloacetate decarboxylase, methylviologen-dependent pyruvate oxidoreductase, phosphotransacetylase and acetate kinase, was detected for the oxidative conversion of fumarate to acetate. Pyruvate formate-lyase and NAD-dependent formate dehydrogenase were also found for the production and consumption of formate, respectively. Methylviologen: NAD(P) oxidoreductase was found to be responsible for linkage between these reductive and oxidative pathways. Furthermore, the cell extracts had branched-chain amino acid aminotransferase and methylviologen-dependent branched-chain 2-oxoacid oxidoreductase, concomitantly with NAD-dependent glutamate dehydrogenase. Valine and leucine could be converted to isobutyryl CoA and isovaleryl CoA, respectively, through the sequential catalyses of these enzymes, and consequently to isobutyrate and isovalerate, respectively.

Acetates↗
PubMed2003

Reappraisal of the 20th-century version of amino acid metabolism.

In this article, we advocate the radical revision of the 20th-century version of amino acid metabolism as follows. (1) Classic studies on the incorporation of [15N]ammonia into glutamate, once considered to be an epoch-making event, are not distinctive proof of the ability of animals to utilize ammonia for the synthesis of alpha-amino nitrogen. (2) Mammalian glutamate dehydrogenase has been implicated to function as a glutamate-synthesizing enzyme albeit lack of convincing proof. This enzyme, in combination with aminotransferases, is now known to play an exclusive role in the metabolic removal of amino nitrogen and energy production from excess amino acids. (3) Dr. William C Rose's "nutritionally nonessential amino acids" are, of course, essential in cellular metabolism; the nutritional nonessentiality is related to their carbon skeletons, many of which are intermediates of glycolysis or the TCA cycle. Obviously, the prime importance of amino acid nutrition should be the means of obtaining amino nitrogen. (4) Because there is no evidence of the presence of any glutamate-synthesizing enzymes in mammalian tissues, animals must depend on plants and microorganisms for preformed alpha-amino nitrogen. This is analogous to the case of carbohydrates. (5) In contrast, individual essential amino acids, similar to vitamins and essential fatty acids, should be considered important nutrients that must be included regularly in sufficient amounts in the diet.

Amino Acids↗
PubMed1989

In-vitro stimulation on the rat epitrochlearis muscle. II. Effects of catecholamines and nutrients on protein degradation and amino acid metabolism.

The influence of catecholamines and branched-chain amino acids (BCAA) plus insulin on protein degradation and amino acid metabolism was investigated in isolated and electrically stimulated rat epitrochlearis muscles. 10(-7) M adrenaline significantly increased the total amount of muscle tyrosine during 40 min of stimulation with 50 Hz (I s min 1) pulse trains. On the other hand, BCAA + insulin at normal and five times normal plasma concentrations had no effect on muscle tyrosine. Muscle 3- methylhistidine was not influenced by any of the treatments. Muscle release and content of aspartate, alanine, glutamate and glutamine showed individual response characteristics to catecholamines and BCAA + insulin. The data indicate that adrenaline can induce an increased total protein degradation in rat fast muscle during acute contractions in vitro and, furthermore, that BCAA + insulin does not retard protein breakdown during acute muscle contraction.

Amino Acids↗
PubMed2001

Influence of N-acetylcysteine on hepatic amino acid metabolism in patients undergoing orthotopic liver transplantation.

Experimental treatment with the antioxidant and glutathione precursor N-acetylcysteine (NAC) has been performed in orthotopic liver transplantation (OLT) to reduce reperfusion injury. To investigate the effect of NAC on the hepatic and intestinal amino acid metabolism, intraoperative amino acid exchange rates were studied in liver transplant recipients with high dose NAC treatment (n = 10) and in control patients (n = 9). Treatment with NAC was found to cause a loss of amino acids and increased urea nitrogen release from the liver graft. The net balance of most amino acids was shifted to increased hepatic release or decreased hepatic uptake. The initial cumulative splanchnic release of all proteinogenic amino acids in the NAC treated group was significantly higher than in the control group. These findings are tentatively explained by an increased net protein catabolism in the liver. The increased hepatic urea and glutamine production rate of the NAC treated patients is expected to increase the energy and oxygen demand of the liver in this critical situation. Thus, NAC may have caused marked metabolic disturbances in the freshly implanted graft. The dosage of NAC should therefore be modified to avoid these disadvantages.

Acetylcysteine↗
PubMed1982

[Disorders of amino acid metabolism in a patient with identified thiamine deficiency].

Report on a serious disturbance of amino-acid metabolism in a 56 year old male patient suffering from thiamine-(vitamin B-1) deficiency, as proven by clinical history and examination and by laboratory data. In comparison with a group of 75 normal male persons also evaluated by the same laboratory this patient--while thiamine deficient--had markedly elevated serum concentrations outside the physiologic range of glutamic acid, glutamine, proline, citrulline, ornithine, histidine, lysine, phenylalanine, tyrosine and leucine, whereas his serum concentrations of taurine, serine and isoleucine were comparably definitely lowered. Following six to seven days of daily i.m. injections of 200 mg of thiamine each, this imbalance of amino-acid homeostasis disappeared except for that of taurine and--questionably--that of phenylalanine. In view of the absence of other exogenous or endogenous potential causes for this, it must be presumed that the thiamine-pyrophosphate deficiency caused the imbalance of amino-acid metabolism by consecutively disturbing the function of the alpha-ketoglutarate-, pyruvate- and p-hydroxy-phenylpyruvate- decarboxylase chains respectively. Possible connections between thiamine-deficiency and lowered serum concentrations of serine, taurine and isoleucine are being discussed.

Amino Acids↗
PubMed1992

Inborn errors of amino acid metabolism. The best strategy for their diagnosis.

We performed a cost-effectiveness analysis to evaluate whether a pediatrician who suspects an inherited disease of amino acid metabolism should refer the child to a specialist in inborn errors of amino acid metabolism or should prescribe the usual screening test, chromatography of amino acids. Actual hospital costs were used to value the referral, the tests, and the complications that occur when the diagnosis is not recognized. The percent of confirmed diagnoses was chosen as a measure of effectiveness. We conclude that it is more cost-effective for a pediatrician to refer the child to a specialist, that the best strategy in the absence of a referral is to prescribe thin-layer chromatography, and that the least cost-effective strategy is to perform ion-exchange chromatography immediately.

Amino Acid Metabolism, Inborn Errors↗
PubMed2002

Regional muscle and adipose tissue amino acid metabolism in lean and obese women.

The effect of obesity on regional skeletal muscle and adipose tissue amino acid metabolism is not known. We evaluated systemic and regional (forearm and abdominal subcutaneous adipose tissue) amino acid metabolism, by use of a combination of stable isotope tracer and arteriovenous balance methods, in five lean women [body mass index (BMI) <25 kg/m(2)] and five women with abdominal obesity (BMI 35.0-39.9 kg/m(2); waist circumference >100 cm) who were matched on fat-free mass (FFM). All subjects were studied at 22 h of fasting to ensure that the subjects were in net protein breakdown during this early phase of starvation. Leucine rate of appearance in plasma (an index of whole body proteolysis), expressed per unit of FFM, was not significantly different between lean and obese groups (2.05 +/- 0.18 and 2.34 +/- 0.04 micromol x kg FFM(-1) x min(-1), respectively). However, the rate of leucine release from forearm and adipose tissues in obese women (24.0 +/- 4.8 and 16.6 +/- 6.5 nmol x 100 g(-1) x min(-1), respectively) was lower than in lean women (66.8 +/- 10.6 and 38.6 +/- 7.0 nmol x 100 g(-1) x min(-1), respectively; P < 0.05). Approximately 5-10% of total whole body leucine release into plasma was derived from adipose tissue in lean and obese women. The results of this study demonstrate that the rate of release of amino acids per unit of forearm and adipose tissue at 22 h of fasting is lower in women with abdominal obesity than in lean women, which may help obese women decrease body protein losses during fasting. In addition, adipose tissue is a quantitatively important site for proteolysis in both lean and obese subjects.

Abdomen↗
PubMed1994

Interaction between valproate and branched-chain amino acid metabolism.

Structural similarities between valproate metabolites and metabolites formed from the beta-oxidation of branched-chain amino acids (isoleucine, leucine, and valine) suggest that valproate may utilize key enzymes of branched-chain amino acid metabolism. Genetic deficiencies in these enzymes may decrease beta-oxidation of valproate and increase formation of valproate hepatotoxic metabolites. We attempted to determine if valproate interacts with branched-chain amino acid enzymes and also evaluated the effect of valproate on the urinary excretion of the straight-chain fatty acids butyrate (C4), valerate (C5), and hexanoate (C6). We collected dosage interval urine samples from three groups of 10 valproate patients: (1) valproate monotherapy, (2) valproate with carbamazepine, and (3) valproate with phenytoin. We also collected 12-hour urine samples from 10 normal volunteers who served as controls. Valproate caused a significant increase in the excretion of the deaminated acid metabolites of valine, isoleucine, and leucine. There were also significant increases in the excretion of the isoleucine metabolites 2-methylbutyrate and 2-methyl-3-OH-butyrate in the valproate patients. Valproate caused a significant increase in the excretion of all three of the straight-chain fatty acids evaluated, and valproate appears to inhibit the four types of acyl-CoA dehydrogenases involved in branched-chain amino acid and short- and medium-chain fatty acid metabolism.

Adult↗
PubMed1983

[Manifold reflection infrared spectroscopy of the hair of mice with an experimental amino acid metabolism disease (L-acetidin-2-carboxylic acid incorporation instead of proline). A model for the use of infrared spectroscopy as a screening method for metabolic diseases].

8 mice were given L-acetidin-2-carboxylic acid orally over a period of 5 weeks. Another 8 mice served as control animals. Finally, the mice were sacrificed, their hair samples were hydrolized and applied to thin layer chromatography which revealed the incorporation of L-acetidin-2-carboxylic acid into mouse hair expressed by an additional spot. This experimental amino acid metabolic disorder served as a model for the application of infrared spectroscopy for screening hair in order to check metabolic disorders. As the multiinternal reflection-infrared spectra showed significant differences we suggest that infrared spectroscopy can be used as a noninvasive screening technique.

Amino Acid Metabolism, Inborn Errors↗
PubMed1987

Protein and amino acid metabolism and requirements in older persons.

In this short review, some aspects of body protein and amino-acid metabolism during aging in human subjects have been explored. There is a progressive diminution of total body protein with aging, due largely to a decline in the size of the skeletal muscle mass. These changes are accompanied by a shift in the overall pattern of whole body protein synthesis and breakdown, with muscle mass estimated to account for about 30 per cent of whole body protein turnover in the young adult, as compared with a lower value of 20 per cent or less in the elderly subject. Because skeletal muscle mass plays an important role in the response of body protein and amino-acid metabolism to stress, such as infection and trauma, this decline in the contribution of muscle to total body protein metabolism might be a factor responsible for the reduced ability of older people to withstand unfavorable circumstances. The determination of the dietary requirements for individual essential amino acids and for total protein has been discussed, and it is evident that the data are limited and often contradictory. However, elderly individuals are more likely to be affected by various biological, environmental, and social factors, which would generally increase protein needs above those for younger adults. Thus, in practice, the protein needs in the elderly are likely to be higher than those in the young. The decline in energy intake, together with its possible consequences for reducing the efficiency of dietary protein utilization, also will tend to increase the protein need for elderly subjects, relative to that for physically more active young adults. Until more data become available, it is recommended, for food planning purposes, that an appropriate protein allowance would be 12 to 14 per cent of the total energy intake, for mixed protein sources characteristic of the diets of industrialized countries or the more affluent sector of populations in developing countries. Energy intake should be at a level that meets the estimates proposed by FAO/WHO/UNU8 for older persons. Higher levels of protein intake would be required to achieve tissue protein repletion following periods of undernutrition or increased body protein (nitrogen) losses due to stressful stimuli of physical or psychological origin.

Adult↗
PubMed2003

Regulation of sulfur amino acid metabolism in men in response to changes in sulfur amino acid intakes.

We showed previously that 64% of the total dietary sulfur amino acid (SAA) requirement could be supported by dietary cysteine (Cys). However, the observation of such a sparing effect may be affected by the dietary intakes of SAA provided. The aim of this study was to compare methionine (Met) metabolism and transsulfuration (TS) in five healthy men fed three different diets (in random order) for 3 d each, with varying combinations of Met and Cys: 24 mg Met/(kg. d) and no Cys (diet A); 13 mg Met/(kg. d) and 11 mg Cys/(kg. d) (diet B); and 5 mg Met/(kg. d) and 19 mg Cys/(kg. d) (diet C). On d 3, Met kinetics and TS were assessed using orally administered L-[1-(13)C, methyl-(2)H(3)]methionine. Met demethylation (transmethylation, TM) significantly decreased as the dietary Met to Cys ratio decreased. Met TS was significantly lower during diets B [2.8 +/- 0.4 micro mol/(kg. h)] and C [1.5 +/- 0.5 micro mol/(kg. h)] than during diet A [7.8 +/- 2.9 micro mol/(kg. h)] (P < 0.05). The results of the present study indicate that when the ratio of Met to Cys fed is typical of that found in major food proteins and total SAA are sufficient to meet requirements, TS is significantly reduced compared with the case in which SAA needs are supplied by Met alone. We conclude that Cys sparing occurs through an increase in the fraction of the homocysteine pool destined for RM relative to TS (RM:TS).

Adult↗