Abstract
The mollusc myoglobin possesses naturally occurring substitution at the distal E7 position (Val-E7) and its oxygen affinity is only slightly lower than those of the common mammalian myoglobins possessing the usual His E7. The structure-function relationship in this myoglobin is notexplained on the basis of the results obtained from the study of the site-directed mutation at the E7 position of mammalian myoglobin. The recent mutation, crystallographic and nuclear magnetic resonance spectroscopy studies have revealed that a guanidino NH proton of Arg E10 in the mollusc myoglobin serves as an alternative hydrogen-bond donor to the bound ligand to maintain a high ligand affinity. The functional properties of the mollusc myoglobin possessing the Val E7 are controlled by a mechanism different from that of the mammalian myoglobin possessing His E7.
