Genetic variation and functional properties of Atlantic cod hemoglobins:: Introducing a modified tonometric method for studying fragile hemoglobins

Hemoglobin polymorphism in Atlantic cod has been investigated with respect to physiological performance at 10, 15 and 20 degrees C applying a modified tonometric method for O-2 equilibrium analysis with full control of the equilibrating gas mixture. The results did not indicate any dissociation of the hemoglobins by a reduction in cooperativity and a parallel increase in affinity during the analytical procedure in contrast to the original tonometric method. With the applied preparation technique, we could store the hemolysate for 10 days at -25 degrees C without any significant changes in the O-2 binding properties (P < 0.05) demonstrating the high quality of this procedure for analysing fragile fish hemoglobins. The present investigation demonstrates that the oxygen affinity of the hemoglobins varied between the genotypes. At all temperatures, except 20 degrees C and pH 8.0, Hb-I(2/2) had a higher O-2 affinity than Hb-I(1/1). These results conform with previous results (16), suggesting Hb-I(2/2), the genotype which is the dominant allele in northern areas, to Dt the most efficient O-2 carrier at low temperatures. The highest O-2 affinity, however, was found fur Hb-I(2/2b), supporting the results of Fyhn et al. (9), that this genotype is more restricted to coastal and warmer water and thus a better marker of the coastal population. Our results further suggest a correlation between genotype specific growth rates and oxygen affinities at all temperatures studied, with the highest growth rates observed in those genotypes having the highest O-2 affinities. In conclusion, the hemoglobin polymorphism of cod seems to be correlated with physiological performance. (C) 1998 Elsevier Science Inc.