Respiratory Functions of Body Fluids 



303 



TABLE 53 (continued). SEDIMENTATION RATE IN CM. x IQ-" /SEC. /DYNE 



REDUCED TO 20° IN WATER AS DETERMINED BY ULTRACENTRT 



FUGATION; CALCULATED MOLECULAR WEIGHTS AND 



ISOELECTRIC POINTS OF BLOOD PIGMENTS 



Data from Svedberg and Pedersen"" and others. 



Figures in parentheses represent secondary and lower sedimentation rates. 



large molecules might be made of units each of a molecular weight of approxi- 

 mately 34,500. 



Table 53 also gives the isoelectric points of different hemoglobins as deter- 

 mined cataphoretically.^^'* In general the invertebrate pigments (erythrocru- 

 orins) have a lower isoelectric point than the vertebrate hemoglobins. 



Summary. Hemoglobins are derived from widely distributed hemochromo- 

 gens. The heme is similar in all of them except for slight differences in 

 absorption bands in certain worms and holothurians. Species differences in 

 the proteins are indicated by crystallographic properties (Ch. 4), solubilities, 

 molecular size and isoelectric points. 



Chlorocruorin. Chlorocruorin, the green iron-containing blood pigment 

 of the sabellid and serpulid worms, has a porphyrin which differs from heme. 

 Oxychlorocruorin of Spirographis, reduced chlorocruorin, and carboxychloro- 

 cruorin show maximum absorption bands toward the red, compared with 

 analogous hemoglobin bands (Table 52).'^" The iroa content of Spirographis 

 chlorocruorin is 1.27 per cent.''" The amino acid composition of the protein 

 is different from the composition in hemoglobins. 



In molecular size, as judged by sedimentation rate, chlorocruorin is similar 

 to the hemoglobins carried in solution in plasma, with molecular weights of 

 several million (Table 53). The affinity of chlorocruorin for carbon monoxide 

 (some 570 times that for oxygen) exceeds the CO affinity of any hemoglobin 

 tested. *"" As with hemoglobin, two atoms of oxygen combine per atom ol 

 iron.''^ 



Hemerythrin. Hemerythrin contains iron, but the pigment is not a porphy- 

 rin. The iron content of Sipuncidtis hemerythrin is 1.017 per cent.^'^*^ Heme- 

 rythrin fails to show sharp absorption bands like those of hemoglobin and 

 chlorocruorin. Roche prepared brown-violet crystals from Sipiinctdiis midus 

 hemerythrin which in oxy-form has an absorption peak at 493 m/x and absorbs 

 increasingly toward the shorter wave lengths (425 to 290 m/x.). In Phascolo- 

 sonia there are broad, indefinite bands with maxima around 350 to 500 m/x. 

 in oxyhemerythrin and in the violet in reduced hemerythrin;'*^'' different 

 maxima were reported for Lingida.'^-'' It is probable, therefore, that the heme- 

 rythrins differ considerably among different species. Hemerythrin is similar 

 in molecular weight to mammalian hemoglobin.''^' The isoelectric point of 



