Rat muscle branched-chain ketoacid dehydrogenase activity and mRNAs increase with extracellular acidemia.
The rate-limiting enzyme in branched-chain amino acid catabolism is branched-chain ketoacid dehydrogenase (BCKAD). In rats fed NH4Cl to induce acidemia, we find increased basal BCKAD activity as well as maximal activity in skeletal muscle. Concurrently, there is a > 10-fold increase in mRNAs of BCKAD subunits in skeletal muscle plus an increase in cardiac muscle but not in liver or kidney. There was no increase in mRNA for malate dehydrogenase or for cytosolic glyceraldehyde-3-phosphate dehydrogenase. Evaluation of the translation capacity of BCKAD mRNAs in muscle of acidemic rats yielded more immunoreactive BCKAD whether the proteins were synthesized from muscle RNA using rabbit reticulocyte lysate or directly using postmitochondrial homogenates. Although the RNA from muscle of acidemic rats yielded twice as much BCKAD protein, we found no net increase in mitochondrial BCKAD protein in muscle by Western blotting. Because there is increased proteolysis in muscle of rats with acidemia, the increase in mRNA might be a mechanism to augment BCKAD synthesis and activity in muscle.
England
B K
BK
Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Greiber
S
S
Mitch
W E
WE
Bowers
B A
BA
Herring
W J
WJ
McKean
M
M
Ebb
R G
RG
Price
S R
SR
Danner
D J
DJ
D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000138:Acidosis / Q000201:enzymology*; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D016375:Antisense Elements (Genetics); D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D017931:DNA Primers; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007658:Ketone Oxidoreductases / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D008297:Male; D008929:Mitochondria, Heart / Q000201:enzymology; D008931:Mitochondria, Muscle / Q000201:enzymology; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology*; D014176:Protein Biosynthesis; D015347:RNA Probes; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D013347:Subcellular Fractions / Q000201:enzymology
D016375:Antisense Elements (Genetics); D017931:DNA Primers; D009097:Multienzyme Complexes; D015347:RNA Probes; D012333:RNA, Messenger; D000643:Ammonium Chloride; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)