A structural comparison of ligand-saturated hemoglobin with protoporphyrin globin. I. Reaction with bromothymol blue and sulfhydryl reagents

Protoporphyrin globin, a hemoglobin derivative which lacks iron atoms, has been prepared and its properties compared with those of the fully liganded hemoglobin molecule. The rates of reaction with bromothymol blue, p-hydroxymercuribenzoate and N-ethyl maleimide have been examined. Protoporphyrin globin reacts more rapidly with bromothymol blue than does liganded hemoglobin, and the optical density change accompanying the reaction is larger. Both p-hydroxymercuribenzoate and N-ethyl maleimide react more slowly with protoporphyrin globin than with ligand-saturated hemoglobin. These differences in reactivity are similar to the differences between deoxygenated and oxygenated hemoglobin.