1. A systematic study of the sedimentation constants of the respiratory blood proteins throughout the animal kingdom has been carried out by means of the ultracentrifugal method.
2. Respiratory proteins enclosed in corpuscles have low sedimentation constants. The following values were found for erythrocruorin: capitellide worms and Cyclostomata, 2.1 x 10-13; glyceride worms and lamellibranchians, 3.5 x 10-13; holothurians, 2.6 x 10-13. Hemoglobin characterized by the sedimentation constant 4.4 x 10-13 occurs only in the five higher classes of the vertebrates, viz., Mammalia, Aves, Reptilia, Amphibia, Pisces. Among the reptiles and amphibians an association product of hemoglobin with sedimentation constant 7.1 x 10-13, probably representing a doublet, was often found. This product was never observed in the other classes of the vertebrates.
3. Respiratory proteins dissolved in the plasma have, as a rule, high sedimentation constants. The only exception is the erythrocruorin of the Chironomus larvæ, which has the constant 2.0 x 10-13. All polychæte worms and hirudineans with dissolved pigment have the constant 57.5 x 10-13 (erythrocruorin and chlorocruorin) . A dissociation product of constant 11.7 x 10-13 (probably 1/16 of the normal molecule) is sometimes found. The oligochæte worms have a variety of erythrocruorin of slightly higher constant, 61.9 x 10-13. The crustaceans show as a rule two sedimentation constants, 16.9 and 23.5 x 10-13. The former one, which occurs both in erythrocruorins and hemocyanins, probably represents a molecular weight of one-half of the latter. Species characterized by the latter constant have hemocyanin and give a mixture of both constants in alkaline solution, thus demonstrating the dissociation into half molecules. One crustacean species (Calocaris macandreae) has a hemocyanin constant of 34.0 x 10-13. This sedimentation constant is also characteristic of the hemocyanin of the scorpion (Euscorpius carpaticus). The xiphosuran (Limulus polyphemus) has a hemocyanin of the same constant, but its blood contains two more hemocyanin varieties of constants 16.5 and 59.1 x 10-13 and a dissociation product of constant 6 x 10-13. The erythrocruorin of the gastropods has the same constant, 33.8 x 10-13. The normal hemocyanin of the gastropods, on the other hand, is characterized by the constant 100.1 x 10-13. It forms an association product of constant 133.6 x 10-13 and two dissociation products of constants 16.2 and 61.9 x 10-13 (probably 1/2 and 1/8 of the normal molecule respectively). The constant 60.9 x 10-13 is also found in the amphineuran hemocyanin (Tonicella marmorca). The cephalopods show two constants, 56.2 x 10-13 for the decapods and 50.1 x 10-13 for the octopods. The latter constant has not been observed in any other place and is the only sedimentation exclusively characteristic of an animal group.
4. The significance of the data collected in the present investigation cannot be fully understood until a sufficient number of pH-stability curves and sedimentation equilibrium measurements have been made on respiratory proteins. The few determinations of this kind so far available, however, seem to indicate that all native proteins form a closed system in which only a very limited number of mass and shape types are stable. Reversible association and dissociation reactions take place easily when the pH of the solution is slightly changed. Within a well-defined animal group all species have as a rule respiratory pigments of the same sedimentation constant (or constants) and dissociate in a similar way. Biological kinship, therefore, is usually accompanied by identity in the sedimentation constants. On the other hand, owing to the small number of different constants possible, the same constant must of necessity occur in different animal groups.
1934. Vol. 66, no 2, 191-223 p.