Biological Chemistry - Berezov, T. T., Korovkin, B. F. 1998

Metabolism of Simple Proteins
Specific Pathways of Metabolism for Certain Amino Acids
Metabolism of Branched-Chain Amino Acids

The Catabolism of Branched-chain Amino Acids—leucine, isoleucine, and valine—takes place primarily not in the Liver (the main site for the degradation of most Other Amino Acids), but in Muscle and adipose Tissues, Kidneys, and Brain tissue. Initially, all Three amino acids undergo Transamination with a-ketoglutarate, catalyzed by a single, highly specific enzyme, branched-chain amino acid aminotransferase (EC 2.6.1.42) (which is absent in the liver), yielding the corresponding a-keto acids. Subsequent Oxidative Decarboxylation of these a-keto acids leads to The formation of acyl-CoA derivatives.

Class="center">

It is worth noting that The enzyme catalyzing The oxidative decarboxylation of these a-keto acids is highly specific (similar to the Pyruvate dehydrogenase and a-ketoglutarate dehydrogenase complexes) and likewise requires all five Cofactors (see Chapter 10). A well-known hereditary condition is maple syrup urine disease, caused by a defect in the decarboxylation of these a-keto acids (resulting from the synthesis of a defective dehydrogenase complex). This leads not only to an accumulation of the Amino Acids and a-keto acids in the Blood, but also to their excretion in urine, which acquires a characteristic maple syrup odor. The disease is rare, typically manifests in early childhood, and leads to severe brain dysfunction and death unless the Dietary intake of leucine, isoleucine, and valine is strictly restricted or entirely eliminated.