uroporphyrinogen iii synthase [ uro-synthase ; hydroxymethylbilane hydro-lyase ( cyclizing ) , ec 4.2.1.75 ] , the fourth enzyme in the heme biosynthetic pathway , is responsible for conversion of the linear tetrapyrrole , hydroxymethylbilane , to the cyclic tetrapyrrole , uroporphyrinogen iii .
C0042089
uroporphyrinogen iii synthase
C0020239
hydro-lyase