title: Effects of perfusate leucine concentration on the metabolism of valine by the isolated rat hindquarter.
abstract: Rates of oxidation of valine and release of alpha-ketoisovaleric acid by hindquarters from rats fed a 9% casein diet were measured at intervals over 90 minutes. The hindquarters were perfused with medium containing between 0.03 and 10 mmol/L L-leucine; concentrations of valine and isoleucine were kept constant at 0.2 and 0.1 mmol/L, respectively. The rate of oxidation of [1-14C]valine increased two to threefold when the perfusate contained 0.8 or 1.0 mmol/L leucine but was depressed by 50% when the leucine concentration was 10 mmol/L. The rate of release of alpha-ketoisovaleric acid from the hindquarter was affected little by perfusate leucine concentrations up to 1.0 mmol/L, but release was depressed when perfusate leucine concentration was increased to 10 mmol/L. The rate of release of alpha-ketoisocaproic acid increased with increasing perfusate leucine concentration, as did intracellular alpha-ketoisocaproic acid and leucine concentrations. These results indicate that valine oxidation by the isolated perfused hindquarter is stimulated by a high perfusate leucine concentration (1.0 mmol/L), suggesting that this response contributes to the depressed plasma and tissue valine pools of rats fed a high-leucine diet. An excessively high concentration of leucine (10 mmol/L) suppresses valine oxidation, presumably by competing with valine for transmination or transport.
mesh_terms: D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000597:Amino Acids, Branched-Chain / Q000378:metabolism; D000818:Animals; D003653:Decarboxylation; D045782:Hemiterpenes; D006614:Hindlimb; D007651:Keto Acids / Q000378:metabolism; D007658:Ketone Oxidoreductases / Q000378:metabolism; D007930:Leucine / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism; D009132:Muscles / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D010477:Perfusion; D051381:Rats; D014633:Valine / Q000378:metabolism*
chemical_list: D000597:Amino Acids, Branched-Chain; D045782:Hemiterpenes; D007651:Keto Acids; D009097:Multienzyme Complexes; C001505:alpha-ketoisovalerate; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D007930:Leucine; D014633:Valine