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The right answer is – D and E) Porphobilinogen synthase also called ALA dehydratase.

There are 2 enzymes in the pathway of Heme biosynthesis which are inhibited by Lead and these are ALA dehydratase/ Porphobilinogen synthase  and Ferrochelatase (Figure). As a result of inhibition, there is impaired heme biosynthesis.

One of the first manifestations of lead toxicity is anemia. Lead-induced anemia manifests as a microcytic, hypochromic anemia.

As regards other options- 

A) Cytochrome oxidase is a complex of electron transport chain.

B) Protoporphyrinogen oxidase is an enzyme for the conversion of Protoporphyrinogen IX  to Protoporphyrin IX (See figure)

C) ALA synthase is the first  enzyme of heme bio synthetic pathway, that catalyzes the condensation of Glycine and Succinyl co A (See figure)















Figure- showing steps of heme biosynthesis and the inhibition of ALA dehydratase and ferrochelatase  by lead.

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