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J. Biochem, 1997, Vol. 121, No. 4 654-660
© 1997 Japanese Biochemical Society

research-article

Remarkable Functional Aspects of Myoglobin Induced by Diazaheme Prosthetic Group1

Saburo Neya*,2, Hiroshi Hori{dagger}, Kiyohiro Imai{ddagger}, Yasuko Kawamura-Konishi§, Haruo Suzuki§, Yoshitsugu Shiro||, Tetsutaro Iizuka|| and Noriaki Funasaki*

*Department of Physical Chemistry, Kyoto Pharmaceutical University Yamashina-ku, Kyoto 607
{dagger}Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University Toyonaka, Osaka 560
{ddagger}Department of Physicochemical Physiology, Medical School, Osaka University Suita, Osaka 565
§Department of Biosciences, School of Science, Kitasato University Sagamihara, Kanagawa 228
||Institute of Physical and Chemical Research (RIKEN) Saitama 351-01

2To whom correspondence should be addressed. Tel: +81-75-595-4664, Fax: +81-75-595-4762

The iron complex of ß,{delta}-diazamesoporphyrin III, a molecular hybrid of porphyrin and phthalocyanine, was incorporated into apomyoglobin to investigate novel biological aspects of myoglobin. The reconstituted ferric protein forms an internal hemichrome with the iron-bound distal histidine. The reduced ferrous protein has extraordinarily high affinities for O2 and CO. The ferrous myoglobin is capable of strong binding with pyridine, imidazole, cyanide, and azide, and reacts moderately with ammonia. The NO complex exhibited 5-coordinate to 6-coordinate transition over 150 min. The instability of 5-coordinate NO heme is consistent with a high affinity of imidazole to the ferrous heme. The kinetic analyses of the ferrous derivatives suggest the importance of the {pi} orbitals in neutral ligands as well as the negative charges in anionic ligands. A high affinity of imidazole to ferrous diazaheme accounts for the internal hemochrome formation in ferrous myoglobin containing phthalocyanines.

1This work was supported by grants from the Scientific Research Foundation of Kyoto Pharmaceutical University, the Ministry of Education, Science, Sports and Culture of Japan (#07308071), and the Japan Private School Promotion Foundation.


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