Effect of dietary protein on the liver content and subunit composition of the branched-chain alpha-ketoacid dehydrogenase complex.
Levels of expression of two subunits of the liver branched-chain alpha-ketoacid dehydrogenase complex in response to extremes of dietary protein intake (50% versus 0% protein diet) were determined by quantitative immunoblotting. Dietary protein deficiency decreased the amount of E1 alpha protein to a greater extent than E2 protein. The ratio of E1 alpha to E2 was below 1 in the liver of animals starved for protein and above 1 in the liver of animals fed the high-protein diet. Supplementation of the 0% protein diet with 5% leucine (but not 5% valine) had the same effect as the 50% protein diet. The extremes of dietary protein also resulted in a divergent pattern of expression of the mRNAs for the subunits of the complex. The E1 beta message showed the expected corollary of being greater in the liver of the high-protein-fed rats than the no-protein-fed rats. In contrast, the E2 message was not affected by the two extremes of dietary protein and the E1 alpha message was greater in the liver of the no-protein-fed rats than the high-protein-fed rats. Thus, coordinate regulation of gene expression of the subunits of the complex does not occur in response to dietary protein. Post-transcriptional regulatory mechanisms most likely determine the amount of the complex and the ratio of its subunits. The decrease in E1 alpha/E2 protein ratio that occurs in dietary protein deficiency may increase sensitivity of the complex to phosphorylation-mediated inhibition by branched-chain alpha-ketoacid dehydrogenase kinase.
Zhao
Y
Y
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis 46202-5122.
Popov
K M
KM
Shimomura
Y
Y
Kedishvili
N Y
NY
Jaskiewicz
J
J
Kuntz
M J
MJ
Kain
J
J
Zhang
B
B
Harris
R A
RA
D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D004044:Dietary Proteins / Q000494:pharmacology; D007658:Ketone Oxidoreductases / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D046911:Macromolecular Substances; D008297:Male; D008930:Mitochondria, Liver / Q000201:enzymology; D009097:Multienzyme Complexes / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D011502:Protein-Energy Malnutrition / Q000201:enzymology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D004044:Dietary Proteins; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D012333:RNA, Messenger; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)