Abstract: A protein inhibitor from Sulfolobulus Solfataricus and peptides thereof, which both have the ability to inhibit AARE and elastase. Similarly to the eukaryotic counterparts, the recombinant protein is able to inhibit in vitro the bovine alfa-chymotrypsin with a high specificity, and the porcine elastase but not all commercial available trypsins, features which distinguish all the members belonging to the family PEBP. Through site-specific mutagenesis techniques of the gene codifying SsCEI, it has been recognized the “reactive site loop”—RCL—on the inhibitor, responsible for the interaction with the eukarial protease target already identified. The inhibitor and the peptides thereof can be used as new compounds capable of modulating cognitive enhancement cardiovascular diseases, cancer, inflammation, hematological diseases, neurological diseases and urological diseases.