Hemoglobin (Hb) is an excellent model for cooperativity analysis and allosterism, fundamental processes in biology. The objective of this work was to analyzing the dissociative properties of lizard (Teiu, Tupinambis merianae) Hbs  through potentiometric titration studies, and the effect of ATP and pH in this process. The potentiometric titrations were done by the gradual addition of degassed potassium ferricyanide 5 mM in the desoxiHb solution, in different pHs in the presence and absence of ATP. The values obtained in potentiometric titrations for the stripped Hb (without organic phosphates) did not show the T®R transition, showing similar results to myoglobin used as reference. However, when we added 1mM of ATP, Hb becomes as an alosteric protein, showing the T®R transition about pH 7,65. The results in potentiometric titrations indicate that, in alkaline pH, probably some dissociation occurred, evidenced by the curve of stripped Hb+ATP had close values of the stripped ones in alkaline pHs. The values of n close to 1, indicate absence of cooperativity and possible dimeric conformation with high oxygen affinity, that would have function to keep this gas during dormancy of the animal. The results in  Hb-O2 affinity corroborate the potentiometric data, with high Hb-O2 affinity and the cooperativity near to 1. This phenomenon may be partially explained by two amino acids replacements in the beta chains, which results in the loss of two negative charges at the a1b2 interface and favors the dissociation into dimers. The mechanism dimer-tetramer transitions during O2 transport, may represent an intermediate stage of evolution to stable tetrameric Hb found in higher vertebrates.