PROPERTIES OF TROUT HBI IN WATER AND LIGAND LINKED BINDING OF NA+

The structural and functional properties of trout Hb I (one of the components isolated from the hemo- lysate of trout, Salmo irideus) have been investigated in considerable detail in the last few years [l-l]. Its properties are exceptional in sofar as ligand binding is characterized by strong heme-heme interactions but lacks completely effects of protons and organic phos- phates. We have investigated the functional properties of trout Hb I in water and in various salts. From the experiments in pure water it is clear that the equilib- rium and kinetics of the isoionic protein are very sim- ilar to those obtained in buffered solutions at different pH values [l-4]. This leads to the conclusion that the characteristic thermodynamic properties of trout Hb I [3] are intrinsic features of the system, and are not dominated by heterotropic effects involving small ions. In addition the oxygen equilibrium of trout Hb I investigated as a function of NaCl, sodium citrate and sodium dextran sulfate shows two distinct effects, one related to the differential binding of Cl- [5] and the other to the specific binding of Na+, which is proven to stabilize the low affinity conformational state of hemoglobin. This effect is discussed in the light of the known structural properties of trout Hb I.