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Abstract Haemoglobin is the respiratory protein of the red blood cells which carries oxygen from the lungs to the tissues and facilitates, both directly and indirectly, the return transport of carbon dioxide. Mammalian haemoglobin has a molecular weight of 64500 and contains two pairs of polypeptide chains: the α-chains with 141 amino acid residues each and the β-chains with 146. Each chain is combined with one haem. Myoglobin, the oxygen carrier of muscle, is closely related to haemoglobin, but has a simpler constitution: it consists of only one polypeptide chain of 153 residues and a single haem. The amino acid sequences of the myoglobins and haemoglobins of man and of several animals have been determined (Dayhoff Watson 1969). All but 21 of its 153 residues form part of helices; over most of their length these helices have conformations closely resembling the right-handed α-helix of Pauling Cullis et al. 1962).
M. F. Perutz (1969) studied this question.