THE DIMER-MONOMER CONVERSION OF CERITHIDEA MYOGLOBIN COUPLED WITH THEHEME IRON OXIDATION

With regard to the distal (E7) residue, gastropod sea mollusc contains both types of myoglobin, one with and the other lacking the distal hi stidine. We have isolated a myoglobin from the radular muscle of Cerit hidea rhizophorarum, a small whelk found on the Japanese coast. Unlike Aplysia myoglobin having a single histidine residue at position 95, C erithidea myoglobin contains three histidines at positions 48, 66 and 98. Moreover, Cerithidea MbO(2) exists as homodimers and is oxidized, not to the usual form of metMb but to the hemichrome monomers. It was also found that the hemichrome monomers thus produced can easily be co nverted back to the dimerized oxy-form, if the ferric protein was redu ced carefully with a slight excess of sodium hydrosulfite. This dimer- monomer conversion coupled with the heme-iron oxidation in Cerithidea myoglobin is very unique, and the distal histidine at position 66 is p robably responsible for its reversible formation of hemichrome from th e ferric met-form that occurred transiently in due course of the oxida tion reaction of Cerithidea MbO(2). Copyright (C) 1996 Elsevier Scienc e Inc.