(1) 5 aminolevulinic acid - ALAD:Zn2+:succinylacetone - ALAD:Zn2+:succinylacetone -> porphobilinogen (2) 5 aminolevulinic acid - ALAD:Zn2+:succinylacetone - ALAD:Zn2+:succinylacetone -> porphobilinogen