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.
Soemitro
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Department of Nutritional Sciences, University of Wisconsin, Madison 53706.
Block
K P
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Crowell
P L
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Harper
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AE
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