Question:medium
Tyrosinosis is caused due to deficiency of which enzyme?
Tyrosinosis is caused due to deficiency of which enzyme?
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Think of the terminal enzyme of tyrosine catabolism whose loss causes liver failure (type I tyrosinemia).
Updated On: Jun 23, 2026
- Fumarylacetoacetate hydrolase
- p-hydroxy phenylpyruvate dehydrogenase
- Tyrosine transaminase
- Tyrosine ligase
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Map the tyrosine degradation route in order: tyrosine $\rightarrow$ p-hydroxyphenylpyruvate $\rightarrow$ homogentisate $\rightarrow$ maleylacetoacetate $\rightarrow$ fumarylacetoacetate $\rightarrow$ fumarate + acetoacetate.
Step 2: Each tyrosinemia type corresponds to a defect at one position. Type I (classic tyrosinosis) sits at the very last hydrolytic split, performed by fumarylacetoacetate hydrolase.
Step 3: When this terminal enzyme fails, succinylacetone accumulates and is hepatotoxic and nephrotoxic, producing the liver-failure phenotype that defines the severe disease. So the deficient enzyme must be the one ending the pathway.
Step 4: By elimination, transaminase loss gives the milder eye-and-skin form (type II) and the dehydrogenase/dioxygenase loss gives type III, while a "ligase" has no role here. \[\boxed{\text{Fumarylacetoacetate hydrolase}}\]
Step 2: Each tyrosinemia type corresponds to a defect at one position. Type I (classic tyrosinosis) sits at the very last hydrolytic split, performed by fumarylacetoacetate hydrolase.
Step 3: When this terminal enzyme fails, succinylacetone accumulates and is hepatotoxic and nephrotoxic, producing the liver-failure phenotype that defines the severe disease. So the deficient enzyme must be the one ending the pathway.
Step 4: By elimination, transaminase loss gives the milder eye-and-skin form (type II) and the dehydrogenase/dioxygenase loss gives type III, while a "ligase" has no role here. \[\boxed{\text{Fumarylacetoacetate hydrolase}}\]
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