Erythrocruorins (extracellular haemoglobins) from the cirratulid polychaetes cirriformia tentaculata (Montagu) and Cirratulus cirratus (Müller) with special reference to saturation dependent characteristics of the oxygen equilibria

Abstract

Erythrocruorins from the intertidal cirratulid polychaetes Cirriformia tentaculata (Montagu) and Cirratulus cirratus (Müller) have a high affinity for oxygen and large Bohr shifts. At low pH, the O 2-equilibrium curves from both species are hyperbolic. In alkaline solution both erythrocruorins show marked increases in O 2-affmity with the retention of the hyperbolic form in Cirriformia. The presence of a pronounced Bohr shift in a non-cooperative erythrocruorin is unusual and its possible physiological rôle is discussed. In Cirratulus, the shape of the curve becomes sigmoidal at high pH. Moreover, the cooperativity coefficient, n, increases at high O 2-saturation. The Bohr effect thus increases in magnitude with rising pH and it is saturation dependent. The significance of this complex oxygen transport system is discussed. The findings illustrate the remarkable elasticity of functions possible in erythrocruorins from closely related species in response to different environmental or metabolic dictates.