Differential scanning calorimetry was used to investigate the thermal unfolding of actin specifically cleaved within the DNaseI-binding loop between residues Met47-Gly48 or Gly42-Val43 by two bacterial proteases, subtilisin or ECP32⁄grimelysin (ECP), respectively. The results obtained show that both cleavages strongly decreased the thermal stability of mono-meric actin with either ATP or ADP as a bound nucleotide.