Protozoan myoglobin from Paramecium caudatum

• Published in: European Journal of Biochemistry
• Main Authors: TSUBAMOTO, Yoshiharu, MATSUOKA, Ariki, YUSA, Keisuke, SHIKAMA, Keiji
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1990
• Subjects: Sperm whale
• Online Access: http://dx.doi.org/10.1111/j.1432-1033.1990.tb19303.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1432-1033.1990.tb19303.x; https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1990.tb19303.x

Native oxymyoglobin (MbO 2 ) was isolated directly from the cells of Paramecium caudatum with complete separation from metmyoglobin (metMb) on a DEAE‐cellulose column. It was examined for its spectral and stability properties. When compared with sperm whale MbO 2 used as a reference, Paramecium MbO 2 was found to be much more susceptible to autoxidation over a wide range of pH (4–11) in 0.1 M buffer at 25°C. Kinetic analysis has revealed that a proton‐catalyzed displacement of O 2 − from MbO 2 by an entering water molecule can play a dominant role in the autoxidation reaction of Paramecium MbO 2 to metMb, as in the case of sperm whale MbO 2 involving the distal histidine as its catalytic residue. At pH values higher than 9.5, however, Paramecium MbO 2 was found to be oxidized to yield a hemichrome. The spontaneous formation of hemichromes is at variance with the other known myoglobins and is therefore discussed in relation to the unusual amino acid sequence of Paramecium myoglobin having a large number of deletion [Iwaasa, H. et al. (1989) J. Mol. Biol. 208 , 355–358].