These studies are carried out with P. R. Ortiz de Montellano's group at U.C. San Francisco. In all projects, modern molecular biology techniques provide site-directed mutants that permit alterations in structures and reactivities. His25A mutants were prepared. The absence of the fingerprint frequency in only the latter species clearly identified His 25 as the axial ligand. Remarkably, when imidazole was added to the inactive H25A preparation, activity was fully restored.
Current effort is underway to identify specific amino acids implicated in the oxidative catalysis.
Heme oxygenase-1, intermediates in verdoheme formation and the requirement for reduction equivalents. Replacement of the proximal histidine iron ligand by a cysteine or tyrosine converts heme oxygenase to an oxidase. Replacement of the distal glycine 139 transforms human heme oxygenase-1 into a peroxidase. We studied the reactions of the enzyme with cyanide an found that it causes reduction of b 595 . A new feature at 639 nm suggests binding of CN - by the chlorin.