Heme is a critical biomolecule that carries out several functions in nearly all life forms, including humans where its most widely known role is mediating oxygen transport in the blood. Heme production must be tightly controlled as alterations in cellular heme levels can lead to multiple diseases. The first and rate-limiting enzyme controlling heme biosynthesis is aminolevulinic acid synthase (ALAS). ALAS is conserved in α-proteobacteria and non-plant eukaryotes; however, there are several unique regions observed only in eukaryotic ALAS enzymes in which alterations have pathological consequences. We seek to understand how ALAS interacts with accessory proteins as well as organism-specific differences in protein assembly that may alter the regulation of heme production. We use structural biology combined with biophysical and biochemical characterization of various eukaryotic ALAS enzymes to parse apart the role of these key regulatory regions in eukaryote physiology. Our work is beginning to reveal key structure-function relationships between these divergent elements and ALAS enzyme function, thus controlling heme biosynthesis.