Bookshelf

Major pathways of branched-chain amino acid metabolism. Maple syrup urine disease is caused by a congenital deficiency of reaction 2. Many of the primary organic acidurias, for example, isovaleric acidemia and methylmalonic acidemia, are referable to inherited defects of enzymes involved in the oxidation of organic acids derived from the branched-chain amino acids. Enzymes: 1, branched-chain amino acid transaminase; 2, branched-chain amino acid decarboxylase; 3, isovaleryl-CoA dehydrogenase; 4, glycine-N-acylase; 5, 3-methylcrotonyl-CoA carboxylase; 6, crotonase; 7, 3-methylglutaconyl-CoA hydratase; 8, 3-OH-3-methylglutaryl-CoA lyase; 9, 2-ketothiolase; 10, isobutyryl-CoA dehydrogenase; 11, propionyl-CoA carboxylase; 12, methylmalonyl-CoA mutase; 13, 3-OH-isobutyryl-CoA deacylase. TPP, thiamine pyrophosphate; LipA, lipoic acid; ETF, electron transfer flavoprotein; AdoB₁₂, adenosylcobalamin; IVA, isovaleric acid; IVG, isovalerylglycine; TCA, tricarboxylic acid.