Streptococcus pyogenes (group A Streptococcus – GAS) is an important gram-positive extracellular bacterial pathogen responsible for a number of suppurative infections. This microorganism developed complex virulence mechanisms to avoid host defense. We have previously revealed that Supernatant of Destroyed Streptococcal Cells (SDSC) from GAS type M22 causes endothelial cells’ dysfunction, inhibits cellular adhesion, migration, metabolism and proliferation in a dose-dependent manner without affecting cells’ viability. The present work is aimed at isolation and characterization of a component from GAS type M22 supernatant that suppresses proliferation of endothelial cells EA.hy926. Isolating a protein possessing antiproliferative activity allowed identifying arginine deiminase (AD). Further study showed that the enzyme is most active at pH 6.8. Calculating Km and Vmax gave the values of 0.67 mM and 42 s-1, respectively. Distinctive feature of AD purified from GAS type M22 is the closest to neutral pH optimum of