The functional properties of hemoglobins from Triturus rristutus curnij2.x have been characterized both from an equilibrium and a kinetic point of view. A special attention has been given to the effect of organic phosphates in view of their role in the modulation of the hemoglobin function. Under stripped conditions newt hemoglobins display a negative Bohr effect which becomes much less pronounced in the presence of 0.2 M inorganic phosphates.The effect of organic phosphates involves not only a drop in the 0, affinity but also a large changc in the shape of the 0, Bohr effect which becomes markedly positive in the presence of my-inositol hexakis(ph0sphate). The experimental data reported make it possible to give a complete picture of the functional behaviour of newt hemoglobins, making a contribution to clarifying the dependence of the sign of the Bohr effect on the acclimatization temuerature of the animxls that has been Dreviouslv reported [Morpurgo, G., Battaglia, P. A. and Leggio, T. (1970) N a t k (Lond.) 225, 76 -771.Respiratory proteins exhibit a great deal of variation in their absolute ligand affinities and in their susceptibility to control by metabolic effectors [I]. These functional differences are generally thought to bc a reflection of the variable environincntal conditions in which organisms live and of the different physiological requirements of their tissues. I t is therefore of great interest to study how two mechanisins of control of hemoglobin function, namely homotropic and heterotropic interactions [2], have evolved in different species in order to meet the specific metabolic demands of the corresponding species.As previously reported 133 (see [4] for review) newt hemolysate shows a Bohr effect that is reversed as compared with mammalian hemoglobins. Moreover the Bohr effect was reported by Morpurgo et al. to bc temperature-dependent, having a negative slope at 4 ' C and a positive one at 30 'C.
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