Structure of oxymyoglobin

MYOGLOBIN (Mb) consists of a single polypeptide chain of 153 residues and one haem. It combines reversibly with molecular oxygen which it takes up from the blood and passes on to mitochondria in muscle. In vivo its iron atom remains ferrous, but in vitro it autoxidises to the ferric metmyoglobin (metmb) in which the sixth ligand at the iron is water. Metmb of sperm whale was the first protein structure to be determined1. Takano recently determined the closely related structure of deoxymb by X-ray analysis, while that of COmb has been determined by neutron diffraction (refs 2, 3 and B. P. Schoenborn, personal communication). The most interesting structure, that of oxymb, has proved elusive. Watson and Nobbs tried to determine it by rapid crystallisation and collection of X-ray data at 4 °C, but even so autoxidation obscured the results4. Recent advances in low temperature techniques encouraged me to try again, especially in view of the wide interest in the nature of the iron–oxygen bond5–7.