The catabolism of branched-chain amino acids occurs via 2-oxoacid dehydrogenase in Saccharomyces cerevisiae.
Saccharomyces cerevisiae possesses 2-oxoacid dehydrogenase (EC 1.2.4.4) similar to that found in mammalian cells. The activity is readily detected in cells which have been cultured in a minimal medium containing a branched-chain amino acid. Mutants defective in lipoamide dehydrogenase also lack 2-oxoacid dehydrogenase and are thus unable to catabolize branched-chain amino acids: 2-oxoacids accumulate in the cultures of these cells. The 2-oxoacid dehydrogenase activity is distinct from both 2-oxoglutarate dehydrogenase and pyruvate dehydrogenase, because it could not be detected in assay conditions which permitted the measurement of 2-oxoglutarate dehydrogenase and vice versa. In addition, a strain lacking 2-oxoglutarate dehydrogenase (kgd1::URA3) retained 2-oxoacid dehydrogenase as did a mutant specifically lacking pyruvate dehydrogenase (pda1::Tn5ble). In complex media the specific activity of this enzyme is highest in YEP (yeast extract-peptone)-glycerol and lowest in YEP-acetate and YEP-fructose. 2-Oxoacid dehydrogenase could not be detected in cells which had been transferred to sporulation medium. These results suggest that in S. cerevisiae the catabolism of branched-chain amino acids occurs via 2-oxoacid dehydrogenase, not via the 'Ehrlich Pathway'.
Dickinson
J R
JR
School of Biochemistry and Molecular Genetics, University of New South Wales, Kensington, Australia.
Dawes
I W
IW
D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000597:Amino Acids, Branched-Chain / Q000378:metabolism*; D003470:Culture Media / Q000494:pharmacology; D008058:Dihydrolipoamide Dehydrogenase / Q000235:genetics / Q000378:metabolism; D045782:Hemiterpenes; D007651:Keto Acids / Q000378:metabolism; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism; D007658:Ketone Oxidoreductases / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009154:Mutation; D011768:Pyruvate Dehydrogenase Complex / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
D000597:Amino Acids, Branched-Chain; D003470:Culture Media; D045782:Hemiterpenes; D007651:Keto Acids; D009097:Multienzyme Complexes; D011768:Pyruvate Dehydrogenase Complex; C001505:alpha-ketoisovalerate; D007658:Ketone Oxidoreductases; D007655:Ketoglutarate Dehydrogenase Complex; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D008058:Dihydrolipoamide Dehydrogenase