Abstract
Mutations in the human gene for the enzyme porphobilinogen deaminase give rise to an inherited disease of heme biosynthesis, acute intermittent porphyria. Knowledge of the 3‐dimensionai structure of human porphobilinogen deaminase, based on the structure of the bacterial enzyme, allows correlation of structure with gene organization and leads to an understanding of the relationship between mutations in the gene, structural and functional changes of the enzyme, and the symptoms of the disease. Most mutations occur in exons 10 and 12, often changing amino acids in the active site. Several of these are shown to be involved in binding the primer or substrate; none modifies Asp 84, which is essential for catalytic activity.