306 VII. COMPARATIVE BIOCHEMISTRY OF HEMOGLOBINS 



2. BIOLOGICAL DISTRIBUTION 



In this chapter we define hemoglobins as a class of ferroporphyrin protein 

 compounds, able to combine reversibly with oxygen without oxidation of the 

 iron to ferric. Hemoglobin was formerly thought to be synthesized only by 

 the members of the animal kingdom, but recent work has shown that this is 

 not so. In 1939, Kubo {1589) observed a hemoglobin-like compound in root 

 nodules. This has been investigated by Burris and Haas {38 Jf), Keilin and 

 Wang {1503), and by Virtanen and co-workers {2890,2891), and there is no 

 doubt that it is a true hemoglobin; its relative affinity for carbon monoxide 

 and oxygen, K = 37, is of the order of that found for myohemoglobin. The 

 pigment is the product of symbiosis, since it is not found in pure cultures of 

 Rhizohium or in the roots of the Leguminosae in the absence of nodule forma- 

 tion. Its function in nitrogen fixation is not discussed further in this chapter 

 {cf. however Chapters IX and XIV). 



Hemoglobin is distributed among a number of phyla in the animal kingdom, 

 becoming increasingly important in the more highly evolved phyla. In 

 these, the pigment is found as myohemoglobin in red muscle and as hemo- 

 globin in erythrocytes. In the more primitive vertebrates, the heart muscle 

 is practically the only muscle containing myohemoglobin. In none of the 

 vertebrates is hemoglobin normally found free in the blood. 



In the invertebrates, the presence of hemoglobin in muscle seems to be 

 rare; so far it has been reported in only a few species {125,2206). In Gastro- 

 philus larvae the pigment is found in special cells known as tracheal cells, 

 which probably originate from fat-body cells {cf. for example 1.503a). A 

 variation is found in the circulatory system, in that hemoglobin is sometimes 

 found in corpuscles and sometimes in physical solution like hemocyanin. 



In 1839, Milne-Edwards {1956) first drew attention to the green blood of 

 certain polychetes. The pigment was subsequently investigated by Lankester 

 {16Jf6) in the 1860"s and by Krukenberg {158.5) and MacMunn {18^0) in 

 the 1880's. Lankester named the pigment chlorocruorin. Although Sorby 

 {2596) in 187G first observed that the spectrum of the red invertebrate 

 hemoglobin differed from that of mammahan hemoglobin, it was not until 

 Svedberg {2708,2713-2715) investigated the physical properties of these 

 pigments in the 1930's that their protein was shown to differ from mammalian 

 globin. He revived the name erythrocruorins, first proposed in 1870 by Ray 

 Lankester {16^6), who subsequently dropped it in favor of invertebrate 

 hemoglobin. 



Table I shows the general distribution of hemoglobins throughout the 

 animal kingdom. It can be seen that throughout the phyla the oxygen 

 carrier may be found in a number of different tissues. The synthesis of the 

 extracellular pigment takes place of course in certain cells: data referring to 

 the annelids, for example, may be found in Stephenson's monograph {26.30). 

 While it may be convenient to qualify reference to the erythrocruorins by 

 using the terms "intracellular", and "extracellular," the latter class have a 

 large molecule which may well create a "microenvironment" similar to that 

 found surrounding the intracellular pigments {cf. Section 7). 



Some workers {1280, U83) still prefer to use the term "invertebrate 



