Analysis of the data on titration of native and peroxynitrite modified αA- and αB-crystallins by Cu²⁺-ions

The interaction of αA- and αB-crystallins with Cu²⁺ ion modulates their structure and chaperone-like activity which is important for lens transparency. Theoretical analysis of the dependences of fluorescence intensity of native αA- and αB-crystallins and αA- and αB-crystallins modified by peroxynitrite on concentration of Cu²⁺ ions has been carried out. It has been shown that one subunit of native αA-crystallin contains two equivalent Cu²⁺-binding sites. The microscopic dissociation constant for Cu²⁺-αA-crystallin complex (K _diss) was found to be equal to 9.7 µM. For peroxynitrite modified αA-crystallin the K _diss value is equal to 17 µM. One subunit of native αB-crystallin contains two non-equivalent Cu²⁺-binding sites. The corresponding microscopic dissociation constants for Cu²⁺-αB-crystallin complexes (K ₁ and K ₂) were found to be equal to 0.94 and 36 µM. For peroxynitrite modified αB-crystallin the K ₁ and K ₂ values are equal to 4.3 and 70 µM, respectively.