BCAT

BCAT, or branched-chain amino acid transaminase, is a pyridoxal phosphate–dependent enzyme that catalyzes the reversible transamination of the branched-chain amino acids leucine, isoleucine and valine with α-ketoglutarate, producing their corresponding branched-chain α-keto acids and glutamate. This reaction links the catabolism of branched-chain amino acids to the general nitrogen and amino acid metabolism.

In mammals, there are two main BCAT isoforms: BCAT1, the cytosolic enzyme, and BCAT2, the mitochondrial enzyme. BCAT1 is relatively abundant in the brain and adipose tissue, whereas BCAT2 is highly expressed in skeletal muscle and other peripheral tissues. Both enzymes require pyridoxal phosphate as a cofactor and are part of the aminotransferase family.

In humans and many other organisms, BCATs initiate the catabolism of BCAAs, with the branched-chain α-keto acids further processed by the branched-chain α-ketoacid dehydrogenase complex in mitochondria. In plants and bacteria, BCAT homologs such as ilvE perform similar transamination and contribute to amino acid and nitrogen metabolism, often with broad substrate specificity.

Clinical and research relevance: Altered BCAT expression has been observed in certain cancers, where increased BCAT1 activity may support glutamate production and redox balance, potentially promoting proliferation. In the brain, BCAT activity affects glutamate availability and may influence neurotransmitter pools including GABA through downstream pathways. Ongoing research investigates BCAT as a potential metabolic target in disease and as a contributor to nitrogen flux in plants and microbes.