Phage lytic enzymes are promising antimicrobial agents. Lysins of phages phi11 (LysPhi11) and phi80 alpha (LysPhi80 alpha) can lyse (destroy) cells of antibiotic-resistant strains of Staphylococcus aureus. Stability of enzymes is one of the parameters making their practical use possible. The objectives of the study were to investigate the stability of lysins of phages phi11 and phi80 alpha in storage and functioning conditions, to identify optimum storage conditions and causes of inactivation. Stability of the recombinant LysPhi11 and LysPhi80 alpha was studied using turbidimetry. CD-spectroscopy, dynamic light scattering, and electrophoresis were used to identify causes of inactivation. At 37 degrees C, pH 7.5 and concentration of NaCl not higher than 150 mM, LysPhi11 molecules contain a high percentage of random coils (43%). However, in spite of this the enzyme has high activity (0.4-0.8 OD600nm s(-1) mg(-1)). In storage conditions (4 degrees C and 22 degrees C, pH 6.0-9.0, 10-500 mM NaCl) LysPhi11 is inactivated by a monomolecular mechanism. The optimum storage conditions for LysPhi11 (4 degrees C, pH 6.0-7.5, 10 mM NaCl) were selected under which the time of the enzyme half-inactivation is 120-160 days. LysPhi80 alpha stability is insufficient: at 37 degrees C the enzyme loses half of its activity almost immediately; at 4 degrees C and 22 degrees C the time of half-inactivation of LysPhi80 alpha varies in the range from several hours to 3 days. Despite the common properties in the manifestation of antistaphylococcal activity the kinetic behavior of the enzymes is different. LysPhi11 is a more promising candidate to be used as an antimicrobial agent. (c) 2015 Elsevier Inc. All rights reserved.