| Property | Value | Evidence |
|---|---|---|
| Gene name | **HGD** (synonym: **HGO**) | (pqac-00000000) |
| UniProt ID | **Q93099** | (pqac-00000000) |
| Recommended protein name | **Homogentisate 1,2-dioxygenase** | (pqac-00000000) |
| EC number | **1.13.11.5** | (pqac-00000000) |
| Protein family | **Homogentisate dioxygenase family** | (pqac-00000000) |
| Key domains | **HgmA_C, HgmA_N, Homogentis_dOase, RmlC-like_jellyroll, RmlC_Cupin_sf** | (pqac-00000000) |
| Amino-acid length | **445 aa** | (pqac-00000000, pqac-00000006) |
| Molecular weight | **49,973 Da** | (pqac-00000006) |
| Chromosomal location | **3q21-q23** | (pqac-00000015, pqac-00000016) |
| Quaternary structure | **Functional hexamer**, organized as a **dimer of trimers** | (pqac-00000006) |
| Cofactor | **Fe(II)** non-heme iron | (pqac-00000001, pqac-00000002) |
| Active-site metal ligands | **His335, Glu341, His371** | (pqac-00000006) |
| Primary substrate | **Homogentisate (homogentisic acid)** | (pqac-00000001, pqac-00000007) |
| Reaction catalyzed | Oxidative ring cleavage of homogentisate with incorporation of molecular oxygen | (pqac-00000001, pqac-00000002) |
| Product | **Maleylacetoacetate** (also written **4-maleylacetoacetate**) | (pqac-00000001, pqac-00000007, pqac-00000008) |
| Pathway role | Enzyme in **phenylalanine/tyrosine catabolism**; acts downstream of **4-hydroxyphenylpyruvate dioxygenase (HPPD)** and upstream of maleylacetoacetate isomerization | (pqac-00000007, pqac-00000008, pqac-00000009) |
| Primary tissue expression | Mainly **liver** and **kidney** | (pqac-00000004, pqac-00000005) |
| Additional reported tissue expression | Prostate, small intestine, colon, chondrocytes, synoviocytes, osteoblasts, brain | (pqac-00000005) |
| Subcellular localization | **Cytoplasm / cytosol** | (pqac-00000004, pqac-00000005) |
| Disease association | **Alkaptonuria (AKU)** caused by HGD deficiency or pathogenic variants | (pqac-00000010, pqac-00000011, pqac-00000017) |
| Mutation burden in disease | **212+ variants** reported by 2020; predominantly missense | (pqac-00000011, pqac-00000017) |


*Table: This table summarizes the core molecular, structural, biochemical, localization, and disease-related properties of human HGD/Homogentisate 1,2-dioxygenase. It is useful as a compact reference for the gene’s canonical function and medically relevant annotations.*