| Property | Human OTC summary |
|---|---|
| Gene symbol | **OTC** (ornithine transcarbamylase) (pqac-00000030, pqac-00000032) |
| UniProt ID | **P00480** |
| EC number | **EC 2.1.3.3** (pqac-00000006, pqac-00000024) |
| Gene location | **Xp21.1** on the short arm of the X chromosome (pqac-00000031, pqac-00000032) |
| Gene size | **~73 kb** (pqac-00000030, pqac-00000031, pqac-00000032) |
| Number of exons | **10 exons** and **9 introns** (pqac-00000030, pqac-00000031, pqac-00000032) |
| Precursor molecular weight | **~39.9 kDa** precursor (pqac-00000018, pqac-00000032, pqac-00000033) |
| Mature protein molecular weight | **~36.1 kDa** mature protein (pqac-00000018, pqac-00000032) |
| Amino acids | **354 aa precursor**; **322 aa mature** reported in older review and gene-structure sources, and **321 aa mature** reported in a newer review after leader peptide cleavage (32 aa leader) (pqac-00000030, pqac-00000031, pqac-00000032) |
| Quaternary structure | **Obligate homotrimer**; dish-like trimer with 3-fold symmetry; active sites formed at subunit interfaces (pqac-00000003, pqac-00000015, pqac-00000033, pqac-00000034) |
| Subcellular localization | **Mitochondrial matrix**, with partial/non-covalent association to the **inner mitochondrial membrane** and participation in multienzyme/channeling assemblies (pqac-00000008, pqac-00000011, pqac-00000015) |
| Primary tissues of expression | Highest physiologic expression/activity in **liver** and **small intestine/intestinal mucosa** (pqac-00000006, pqac-00000016, pqac-00000021, pqac-00000035) |
| Km for carbamoyl phosphate | Reported **0.26 mM** in a recent review; older review cites **26 μM** (pqac-00000000, pqac-00000002) |
| Km for ornithine | Reported **0.4 mM** in a recent review; older review cites **40 μM** (pqac-00000000, pqac-00000002) |
| pH optimum | **~pH 8** (pqac-00000001, pqac-00000022) |
| Reaction catalyzed | **Carbamoyl phosphate + L-ornithine → L-citrulline + phosphate (+ H⁺)**; transfer of the carbamoyl group to the δ-amino group of ornithine (pqac-00000000, pqac-00000003, pqac-00000006, pqac-00000017) |
| Key catalytic residues / motifs | Active site spans adjacent subunits; important residues/motifs include **Asp231**, **His168**, **Arg141**, **Arg330**, **Cys303**, **Leu304**; conserved **STRTR** motif in the carbamoyl-phosphate-binding region and **HCLP** motif in the ornithine-binding/catalytic region (pqac-00000004, pqac-00000005, pqac-00000033) |
| Inhibitors | **L-norvaline** (reported **Ki = 71 μM**), **L-α-aminobutyrate**, **γ-aminobutyrate**, **L-leucine**, **L-isoleucine**, **L-valine**, **L-lysine** (alternative substrate/inhibitory competitor), **inorganic phosphate** (product inhibition), **Zn(II)**, and reducing agents (pqac-00000000, pqac-00000002, pqac-00000019) |


*Table: This table summarizes the core biochemical, structural, genetic, and localization properties of human ornithine transcarbamylase (OTC). It is useful as a quick reference for functional annotation and for distinguishing catalytic mechanism, cellular context, and clinically relevant biochemical features.*