Studies on ligand binding to hemoglobins from teleosts and elasmobranchs.

Hemoglobins from three sharks, the porbeagle (Lamno nusus), the dusky (Carcharhinus obscurus), and the mako (Zsurus oxyrinchus), and four bony fishes, the big-eye tuna (Thunnus obesus), the swordfish (Xiphias gladius), the carp (Cyprius carpio), and the smallmouth bass (Micropefrus dolomieu), have been examined by a variety of techniques to determine both their molecular structure and their kinetic and equilibrium ligand-binding properties. For all species multiple hemoglobins were found in the hemolysates. These hemoglobins are tetrameric and exhibit cooperative ligand binding. The main components of the hemolysates from the oceanic species consist of either three or four electrophoretically separable globin chains. However, the hemolysates behave as if they contain only two distinct functional components which appear to be present within the same tetramerit molecule. These two types of ligand-binding sites exhibit different kinetic and spectral properties for the carbon monoxide-binding reaction and for the displacement of oxygen by carbon monoxide. At 20’ the differences between the rates of oxygen dissociation from these two components are largest for the hemoglobins of the mako shark (22.7 s-l and 1.86 s-l) and those of the swordfish (28.2 s-l and 4.8 s-1). Similar albeit smaller differences were observed for porbeagle, dusky, big-eye tuna, and carp hemolysates. The carbon monoxide-binding reactions of these hemolysates were also separable into a fast and slow component with all species showing a rapid reaction on the short wave length side of the 425 nm isosbestic point and a slower reaction on the long wave length side. With the possible exception of big-eye tuna hemoglobin, all of the fish and shark hemoglobins appear to interact with organic phosphates with a stoichiometry of 1 mole bound per mole of hemoglobin tetramer. At neutral pH inositol hexaphosphate lowers the rate of CO binding to swordfish