REMARKABLE FUNCTIONAL-ASPECTS OF MYOGLOBIN INDUCED BY DIAZAHEME PROSTHETIC GROUP

The iron complex of beta,delta-diazamesoporphyrin III, a molecular hyb rid of porphyrin and phthalocyanine, was incorporated into epomyoglobi n to investigate novel biological aspects of myoglobin. The reconstitu ted ferric protein forms an internal hemichrome with the iron-bound di stal histidine. The reduced ferrous protein has extraordinarily high a ffinities for O-2, and CO. The ferrous myoglobin is capable of strong binding with pyridine, imidazole, cyanide, and azide, and reacts moder ately with ammonia. The NO complex exhibited 5-coordinate to B-coordin ate transition over 150 min. The instability of 5-coordinate NO heme i s consistent with a high affinity of imidazole to the ferrous heme. Th e kinetic analyses of the ferrous derivatives suggest the importance o f the pi orbitals in neutral ligands as well as the negative charges i n anionic ligands. A high affinity of imidazole to ferrous diazaheme a ccounts for the internal hemochrome formation in ferrous myoglobin con taining phthalocyanines.