the first and rate-controlling enzyme of the pathway , 5-aminolevulinate dehydrase ( or porphobilinogen synthase ) , and uroporphyrinogen decarboxylase , the activity of which is decreased in porphyria cutanea tarda , a liver disease in which iron is known to play an important but still poorly understood role .
C0042085
uroporphyrinogen decarboxylase
C0162566
porphyria cutanea tarda