| Step Number | Enzyme Name | Gene Symbol | EC Number | Substrate | Product | Associated Disease (when deficient) |
|---|---|---|---|---|---|---|
| 1 | Tyrosine aminotransferase | TAT | EC 2.6.1.5 | L-tyrosine + 2-oxoglutarate | 4-hydroxyphenylpyruvate + L-glutamate | Tyrosinemia type II (Richner-Hanhart syndrome) (pqac-00000004, pqac-00000009, pqac-00000022) |
| 2 | 4-Hydroxyphenylpyruvate dioxygenase | HPD | EC 1.13.11.27 | 4-hydroxyphenylpyruvate | Homogentisic acid (homogentisate) | Tyrosinemia type III (pqac-00000009, pqac-00000022, pqac-00000024) |
| 3 | Homogentisate 1,2-dioxygenase | HGD | EC 1.13.11.5 | Homogentisic acid (homogentisate) | Maleylacetoacetate | Alkaptonuria (pqac-00000009, pqac-00000022, pqac-00000024) |
| 4 | Maleylacetoacetate isomerase (glutathione S-transferase zeta 1) | GSTZ1 | EC 5.2.1.2 | Maleylacetoacetate | Fumarylacetoacetate | Maleylacetoacetate isomerase deficiency (MAAID) (pqac-00000022) |
| 5 | Fumarylacetoacetate hydrolase | FAH | EC 3.7.1.2 | Fumarylacetoacetate | Fumarate + acetoacetate | Tyrosinemia type I (pqac-00000009, pqac-00000022) |


*Table: This table summarizes the complete five-step human tyrosine catabolic pathway from tyrosine to fumarate and acetoacetate. It also links each enzymatic step to the inherited disorder caused by deficiency of that enzyme, making it useful for functional annotation and clinical interpretation.*