Uroporphyrinogen III
N
CH3
CH2
CH
=
N
CH3
CH
CH2
N
CH3
CH2
CH2
.
HOOC
N
CH3
CH2
COOH
CH2
.
The two enzymes that act to join 4 PBG molecules
Reaction occurs in cytoplasm
Uroporophyrinogen
III synthase
Uroporophyrinogen
decarboxylase