1protoporphyrinogen IXdelta-aminolevulinateBlack - reactantsdelta-aminolevulinateRed - side productsrate limiting stepO2H2OALAS1ALAS2CoAURODsuccinyl-CoAFECHprotoporphyrin IXFe2+UROSCO2CO2H+ALADhydroxymethylbilanecoproporphyrinogen IIIHMBSPPOXGlycineporphobilinogenO2NH3H2OprotohemePorphobilinogenCO2H2O2H2OCPOXuroporphyrinogen III