ABSTRACT
Hemoglobin and myoglobin are the two oxygen-binding proteins present in large multicellular organisms. Hemoglobin transports oxygen in the blood and is located in the erythrocytes; myoglobin stores the oxygen in the muscles. Myoglobin was the first protein to have its three-dimensional structure solved by X-ray crystallography. It is a globular protein made up of a single polypeptide chain of 153 amino acid residues that is folded into eight – helices. The heme prosthetic group is located within a hydrophobic cleft of the folded polypeptide chain. Comparison of hemoglobin sequences from different species reveals that only nine amino acid residues are invariant. Some residues are subject to conservative substitution of one residue by another with similar properties, others to nonconservative substitution where one amino acid residue is replaced by another with different properties. Heterozygotes carrying only one copy of the sickle-cell gene are more resistant to malaria than those homozygous for the normal gene.
