Activities of branched-chain amino acid--degrading enzymes in liver from rats fed different dietary levels of protein.
The relationships among dietary protein intake, plasma branched-chain amino acid (BCAA) and keto acid (BCKA) concentrations, and liver BCAA-degrading enzyme activities were investigated in rats fed, for 5 h/d for 2, 6 or 9 d, diets containing from 0 to 50% casein. Plasma, liver and muscle BCAA concentrations were proportional to protein intake over the entire range tested; plasma BCKA concentration, however, was proportional only in the range from 0 to 20% casein, after which a plateau was reached. By d 2, liver cytosolic BCAA aminotransferase activity had increased in rats fed 50% casein; by d 9, activity had increased in rats fed 0 or 5% casein as well. Liver mitochondrial BCAA aminotransferase activity was unresponsive to dietary treatment. Basal liver BCKA dehydrogenase activity and the percent active complex were proportional to protein intake on d 2 and 6. On d 2, total BCKA dehydrogenase activity was the same in all groups; by d 6, total activity had increased in rats fed 30 or 50% casein. We conclude that although the adaptive changes in BCAA-degrading enzyme activities are small, they are sufficient to compensate for excessively high or low protein intakes, so that tolerable concentrations of BCAA and BCKA are maintained.
Department of Nutritional Sciences, University of Wisconsin, Madison 53706.
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Soemitro
K P
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Block
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Crowell
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Harper
D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000597:Amino Acids, Branched-Chain / Q000378:metabolism; D000818:Animals; D001835:Body Weight; D002364:Caseins / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004044:Dietary Proteins / Q000494:pharmacology*; D007651:Keto Acids / Q000378:metabolism; D007658:Ketone Oxidoreductases / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008297:Male; D008930:Mitochondria, Liver / Q000201:enzymology; D009097:Multienzyme Complexes / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D000637:Transaminases / Q000378:metabolism*
D000597:Amino Acids, Branched-Chain; D002364:Caseins; D004044:Dietary Proteins; D007651:Keto Acids; D009097:Multienzyme Complexes; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000637:Transaminases; C019798:branched-chain-amino-acid transaminase