RESPIRATION 



TABLE 4.14 

 Respiratory Characteristics of Haemocyanins 



187 



Function of Chlorocruorin. The chlorocruorin of sabellids normally 

 functions as an oxygen carrier at high tensions. Oxygen capacity of 

 Spirographis blood is 9 vols%, and the dissociation curve is shifted to the 

 right with rise in temperature and increase of acidity. Dissociation con- 

 stants are high {t% = 50, t u = 27, at pH 7-7 and 20°C), permitting the 

 chlorocruorin to function in 2 transport under conditions of abundant 

 oxygen supply (Fig. 4.20). Treatment of Sabella with CO reduces 2 

 consumption over a wide range of 2 tensions (1*1-5*5 c.c. 2 per 1.), 

 showing that a considerable fraction, up to half of the 2 , is transported 

 by chlorocruorin, the remainder being carried in solution (Fig. 4.21). 

 It is interesting that in Serpula, where chlorocruorin and haemoglobin 

 occur together in the blood, both pigments possess equally low oxygen 

 affinities. Chlorocruorin functions as an oxygen transporter under normal 

 conditions and during periods of oxygen depletion (46, 47, 58, 60, 113). 



Function of Haemerythrin. Haemerythrins found in sluggish sipun- 

 culoids have high oxygen affinities. Unloading tensions are low (8 mm Hg) 

 and the dissociation curves are little affected by acidity and C0 2 (Fig. 

 4.20). In the coelomic fluid of Sipunculus the oxygen tension is 32 mm Hg 

 (animal in sea water), at which level the haemerythrin would remain 

 saturated and oxygen transport would depend on gas carried in solution. 

 However, these animals may be periodically exposed to low 2 tensions in 

 littoral regions, when the haemerythrin would subserve 2 transport, as 

 in the littoral worms Arenicola and Urechis, which possess haemoglobins 

 of correspondingly high oxygen affinities. The haemerythrin of the brachio- 

 pod Lingula likewise shows fairly high oxygen affinity (t u and t h 16 and 

 60 mm Hg respectively) (93). 



Function of Haemocyanin. Haemocyanin is the most important blood 

 pigment of molluscs and arthropods (representative dissociation curves, 

 Fig. 4.22). Of these the cephalopods show highest levels of blood copper 

 and oxygen capacity, the latter lying around 4-5 vols % in arterial blood. 

 About nine-tenths of the oxygen is removed in passing through the tissues 

 and is made good by oxygenation in the gills. Oxygen affinity appears to 

 be least in the squid, the most active of cephalopods (Table 4.14). In- 



