THE UNIQUE STRUCTURES OF PROTOZOAN MYOGLOBIN AND YEAST HEMOGLOBIN - AN EVOLUTIONARY DIVERSITY

A hemoglobin-like protein is found in some of the single-celled organi sms, but its structure is quite different from that of mammalian myogl obin or hemoglobin. For instance, a protozoan myoglobin isolated from Paramecium caudatum consists of 116 amino acid residues, so that this contracted form is nearly two thirds of sperm whale myoglobin. Yeast h emoglobin from Candida norvegensis, on the other hand, is composed of a single polypeptide chain with 387 amino acid residues, but of two di stinct domains carrying different functions; that is the N-terminal, h eme-containing region and the C-terminal, FAD-containing reductase dom ain. The very unique structures of these ancient hemoproteins tell us their own strategies to overcome many difficulties in the reversible a nd stable binding of molecular oxygen, a very strong oxidizing agent, to the heme iron(II) in aqueous solutions.