A hemoglobin-like protein is present in some of the single-celled organisms, but its structure is quite different from that of mammalian myoglobin 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 hemoglobin from Candida norvegensis, on the other hand, is composed of a single polypeptide chain of 387 amino acid residues, but of two distinct domains carrying different functions; that is the N-terminal, heme-containing region and the C-terminal, FAD-containing reductase domain.
View full abstract