BACKGROUND: This paper describes the modeling of the kinetics of thermal inactivation of transglutaminase (TGase) from a newly isolated Bacillus circulans BL32, isolated from the Amazon environment. The purified enzyme was incubated at temperatures ranging from 30 to 70 degrees C and values of the thermodynamic inactivation parameters, such as activation energy (Delta E), activation enthalpy (Delta H), activation entropy (Delta S), and free energy (Delta G) for thermal inactivation, were calculated. RESULTS: The kinetics of TGase thermo-inactivation followed a Lumry-Eyring model. The enzyme was very stable up to 50 degrees C, with approximately 50% of activity remaining after heating for 12 h. It was completely inactivated by incubation at 70 degrees C for 2 min. Delta E for TGase was 350.5 kJ mol(-1). Delta H and Delta S for thermo-inactivation of the TGase were 347.8 kJ mol(-1) and 744 J mol(-1) K-1 at 50 degrees C, respectively. Dynamic light scattering measurements suggest that the thermal inactivation of this microbial TGase can be partially attributed to the formation of aggregates. CONCLUSION: These results provide useful information about the thermal characteristics of the microbial TGase from B. circulans BL32 and indicate that this enzyme could be a good candidate for industrial applications. (C) 2009 Society of Chemical Industry