| Isoform | Gene name | Protein name | Subcellular localization | Tissue expression | Chromosomal location | Key structural features | PDB code | Role in disease |
|---|---|---|---|---|---|---|---|---|
| BCAT1 | **BCAT1** | Branched-chain-amino-acid aminotransferase, cytosolic (BCATc) | Cytosol (pqac-00000004, pqac-00000005) | Restricted; enriched in neuronal tissues (brain, spinal cord, retina), and also ovary, testes, placenta, pancreas (pqac-00000004) | Not established from gathered evidence | Redox-active CXXC motif **C335/C338**; PLP-dependent active site with catalytic lysine reported as **Lys222** in structural evidence (pqac-00000010, pqac-00000029) | **2COJ** (pqac-00000029) | Prominent in neurologic/glutamate metabolism; aberrantly expressed in several cancers and linked to tumor progression; bi-allelic variants reported in candidate neurometabolic disorder literature retrieved during search (pqac-00000059, pqac-00000062) |
| BCAT2 | **BCAT2** | Branched-chain-amino-acid aminotransferase, mitochondrial (BCATm); also called placental protein 18/PP18 in older nomenclature | Mitochondria (pqac-00000004, pqac-00000005) | Broad/ubiquitous; highest in skeletal muscle, colon, kidney, pancreas; low in liver (pqac-00000004, pqac-00000005) | **19q13.33** (pqac-00000005) | Redox-active CXXC motif **C315/C318**; PLP-dependent active site with catalytic lysine reported as **Lys202** in BCATm crystal structure; functions as homodimer (pqac-00000012, pqac-00000028, pqac-00000029) | **1EKF** (reduced form); additional BCATm forms **1KTA**, **1KT8** (pqac-00000028, pqac-00000029, pqac-00000032) | Causal gene for ultra-rare **BCAT2 deficiency** with elevated plasma BCAAs and low/normal BCKAs; also implicated in cancer metabolism, ferroptosis resistance, pancreatic cancer growth, melanoma progression, prostate cancer survival signaling, and metabolic disease/insulin-resistance pathways (pqac-00000024, pqac-00000033, pqac-00000040, pqac-00000041, pqac-00000051, pqac-00000054) |


*Table: This table compares the human BCAT1 and BCAT2 isoforms across localization, tissue expression, structural features, and disease relevance. It is useful for distinguishing the cytosolic neuronal isoform from the mitochondrial broadly expressed isoform central to BCAA catabolism.*