The hemoglobins in genetics and evolution / Vernon M. Ingram.

  • Ingram, Vernon Martin, 1924-
Date:
1963
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The hemoglobins in genetics and evolution / Vernon M. Ingram. Source: Wellcome Collection.

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    chains, the same as in the adult type, and two y polypeptide chains chemically distinguishable from the ß polypeptide chains (Schroeder and Matsuda, 1958). We see then that half the molecule is identical with the adult type, but that the other half is different. Also, the normal human adult has a minor hemoglobin component (Kunkel and Wallenius, 1955), called hemoglobin A 2 , which is electro- phoretically distinguishable from the others. Hemoglobin A 2 also has four polypeptide chains in its molecule, two a chains, which are identical with those in the adult protein and in fetal hemoglobin, and in addition two ô peptide chains (Ingram and Stretton, 1961). The symbol ô is used to indicate that these peptide chains are distinguishable in their primary structure from the ß and y peptide chains and are also under separate genetic control (see chapter 4). Altogether then, there are four types of polypeptide chain which make up the three types of hemoglobin found in the human (Figure 2-1)—the oc, ß, y, and ô chains. There is very good genetic evidence to indicate that these four types of peptide chain have their primary structure controlled by four different structural genes. We will discuss the genetic evidence for this statement in a later chapter. The hemoglobins of vertebrates are strikingly similar in their overall structure, with the notable exception of the hemoglobins found in certain cyclostomata (see in Gratzer and Allison, 1960). The vertebrate hemoglobins are all composed of four polypeptide chains of two kinds; for these we can write as in the human a formula of the type of cc 2 ß 2 . In addition there is evidence now that multiple forms of hemoglobin are to be found in certain mammals. An excellent review of this subject has recently been published by Gratzer & Allison (1960). In spite of the overall similarity there are of course structural differences between, for example, rabbit hemoglobin and human hemoglobin. These are differences in the amino acid sequences, but they are really quite few in number and the overall resemblance of the molecule is striking (Muller, 1961 ; Diamond and Braunitzer, 1962; Naughton and Dintzis, 1962). Two other types of human hemoglobin are illustrated in Figure 2-1 ; these are hemoglobin H (Rigas et al., 1955; Gouttas et al., 1955;