Oxidation of leucine by rat liver and kidney

Dawson, Anthony G.; Hird, F. J. R.; Morton, Dougal J.

doi:10.1016/0003-9861(67)90216-0

Cited by 35 publications

(8 citation statements)

References 20 publications

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“…In man, insulin accelerates the disposal of an exogenous load of leucine (19) and hyperinsulinemia inhibits the release of leucine from muscle (20). In vitro studies have demonstrated that insulin enhances the uptake of leucine by muscle (21), adipose tissue (22), and liver and kidney (23), and that insulin promotes protein synthesis (24,25).…”

Section: Discussionmentioning

confidence: 99%

Insulin-mediated reduction of whole body protein breakdown. Dose-response effects on leucine metabolism in postabsorptive men.

Fukagawa¹,

Minaker²,

Rowe³

et al. 1985

J. Clin. Invest.

356

118

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In vivo effects of insulin on plasma leucine and alanine kinetics were determined in healthy postabsorptive young men (n = 5) Leucine oxidation estimated from the GC-enrichment of expired CO2 and plasma leucine (12±1 ,umolkg. hr-) and from the '3C-enrichment of CO2 and plasma a-ketoisocaproate (19±2 Mumollkg. hr-') increased at the 16 ,U/ml insulin level to 16±1 and 24±2 ,mol(kg. h)-', respectively (P < 0.05 for each), but did not increase at higher insulin levels. Alanine flux (206±13 Amol(kg-h)-Y) did not increase during the clamp, but alanine de novo synthesis increased in all studies from basal rates of 150±13 to 168±23, 185+21, 213±29, and 187±15 ,umol(kg. h)-1 at 16, 29, 75, and 2,407 MU/ml insulin levels, respectively (P < 0.05). These data indicate the presence ofinsulin-dependent suppression of leucine entry into the plasma compartment in man secondary to a reduction in proteolysis and the stimulation of alanine synthesis during euglycemic hyperinsulinemia.

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Section: Discussionmentioning

confidence: 99%

Insulin-mediated reduction of whole body protein breakdown. Dose-response effects on leucine metabolism in postabsorptive men.

Fukagawa¹,

Minaker²,

Rowe³

et al. 1985

J. Clin. Invest.

356

118

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“…Thus physiological increments of insulin are known to inhibit the release of leucine and other amino acids from skeletal muscle in the basal state [12]. Moreover, studies in vitro have demonstrated that insulin may stimulate the uptake of leucine by muscle [ 131, adipose tissue [14], liver and kidney [15]. Whether this also applies in intact man is not known.…”

Section: Introductionmentioning

confidence: 99%

Leucine Uptake by Splanchnic and Leg Tissues in Man: Relative Independence of Insulin Levels

et al. 1983

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The influence on leucine disposal of physiological alterations in plasma insulin concentrations was examined in three groups of healthy male subjects, six in each group. After an overnight fast the subjects received an intravenous infusion of either leucine (300 mumol/min for 150 min, series A), or leucine plus glucose (2.2 mmol/min, series B), or leucine, somatostatin (7 micrograms/min) and glucagon (1 ng/min, series C). Arterial concentrations of substrates and their net exchange across the splanchnic and leg tissues were determined with a catheter technique. Insulin concentrations rose from 12 +/- 2 to 20-22 mu-units/ml in series A, from 11 +/- 3 to 60-65 65 mu-units/ml in series B and decreased from 8 +/- 1 to approximately 5 mu-units/ml in series C. The basal leucine concentration for all subjects was 109 +/- 8 mumol/l and it rose progressively during the infusions. In series A, the level was 598 +/- 20 mumol/l after 150 min. The corresponding value was 542 +/- 38 mumol/l in series B and 651 +/- 25 mumol/l in series C. Significant differences were observed between series A and B (P less than 0.05) and series A and C (P less than 0.01) when data for 90-150 min of infusion were combined (analysis of variance). In all groups the leucine infusion resulted in an augmented net uptake of leucine across the leg (77-85 mumol/min) and across the splanchnic bed (61-72 mumol/min) but no significant intergroup differences were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…Is it possible that acyl-CoAs formed in peroxisomes have to be transported to mitochondria for complete catabolism? The a-keto dehydrogenase complexes that use the keto acids derived from leucine, isoleucine, and valine as substrates are at least partly located in mitochondria (22,(24)(25)(26), but a rigorous determination of the cellular distribution apparently has not been done. It should be noted that most peroxisomal enzymes (27,28) originally were thought to have a cytosolic location.…”

Section: Discussionmentioning

confidence: 99%

Isolation and identification of aliphatic short-chain acylcarnitines from beef heart: possible role for carnitine in branched-chain amino acid metabolism.

Bieber¹

1977

Proc. Natl. Acad. Sci. U.S.A.

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Aliphatic acylcarnitines isolated from a water-soluble fraction of beef heart have been characterized by gas chromatography and mass spectrometry. The following acyl residues derived from the acylcarnitine fraction were unequivocally identified: acetyl, pro ionyl, isobutyryl, butyryl, a-methylbutyryl, valeryl, isovalery, tiglyl, and caproyl. flmethylcrotonyl and methacrylyl were tentatively identified. This occurrence of considerable quantities of branched-chain acylcarnitines indicates a role for carnitine in branched-chain amino acid metabolism.Although it is well established that carnitine participates in shuttling long-chain acyl residues across the inner membrane of mitochondria (1-4), some data indicate additional functions for carnitine. Other roles for carnitine are indicated by (i) the multiorganelle location of medium-chain and short-chain carnitine acyltransferases in liver (5-7), (ii) the high activity of carnitine octanoyltransferase in many tissues (8-10), (iii) the occurrence of short-chain acylcarnitines, especially in muscle, some of which apparently are not acetylcarnitine (11-15), and (iv) the clofibrate-induced increase in short-chain and medium-chain carnitine acyltransferase activity (16)(17)(18)(19)).An approach to elucidating broader roles for carnitine would be to identify and quantitate the products of the short chain and medium chain carnitine acyltransferases in specific tissues. These products should be water-soluble and would be found in the water-soluble acylcarnitine fraction. Herein we show that aliphatic branched-chain acylcarnitines constitute a major portion of the water-soluble carnitine fraction isolated from beef heart. METHODS Isolation of Acylcarnitines. Fresh beef heart was obtained from the slaughterhouse and immediately chilled. The fat was removed and the acylcarnitine fractions were isolated therefrom. Water-soluble aliphatic acylcarnitines were isolated and the acyl moieties were separated as described elsewhere (20).Identification of Acyl Residues. The short-chain fatty acids derived from the acylcarnitine fraction were subjected to gas chromatography as described (20) for tentative identification. Positive identification was made by subjecting the individual fatty acid peaks obtained from gas chromatography to mass spectral analyses and comparing with standard free fatty acids. These analyses were performed by the mass spectrometry facilities at Michigan State University, under the supervision of C. C. Sweeley. RESULTSThe water-soluble acylcarnitine fraction was isolated from several rat tissues and from sheep muscle and beef heart. As anticipated, considerable amounts of acetylcarnitine and lesser quantities of propionylcarnitine were found. However, all of the tissues investigated contain several other acylcarnitines. A gas chromatographic profile of the volatile fatty acids obtained from a hydrolysate of the water-soluble acylcarnitines of beef heart is shown in Fig. 1. The prevalence of fatty acids with retention times of C4 and C5 volatile fatty acids...

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Oxidation of leucine by rat liver and kidney

Cited by 35 publications

References 20 publications

Insulin-mediated reduction of whole body protein breakdown. Dose-response effects on leucine metabolism in postabsorptive men.

Insulin-mediated reduction of whole body protein breakdown. Dose-response effects on leucine metabolism in postabsorptive men.

Leucine Uptake by Splanchnic and Leg Tissues in Man: Relative Independence of Insulin Levels

Isolation and identification of aliphatic short-chain acylcarnitines from beef heart: possible role for carnitine in branched-chain amino acid metabolism.

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