Myoglobin of the orangutan as a phylogenetic enigma

Abstract

THE primary structure of the myoglobin of nine anthropoid primates is known from previous work on three ceboids, two cercopithecoids and four hominoids^1,2. The most striking result of these investigations has been the nature of residue 110. With the exception of the cercopithecoids and hominoids this position is occupied by alanine in all mammalian myoglobins known, including those of the South American monkeys. In the Old World monkeys, however, residue 110 is serine, and in man and the three apes so far investigated it is a cysteine. It is noteworthy that two of the codons for Ala can change to codons for Ser by a single point mutation, and each of these can change to a codon for Cys by a further single point mutation. There seemed, therefore, to be an evolutionary sequence Ala → Ser → Cys at this position in myoglobin³. In the α chain of human haemoglobin and that of many other animals the homologous position is also occupied by cysteine⁴. The myoglobin residue at position 23 is also of particular interest among the primates, being serine in the gibbon and the monkeys investigated so far, whereas it is glycine in all other mammalian myoglobins for which the primary structure is known, including those of man, chimpanzee and gorilla.