Photoreactions of 1,4-naphthoquinone with lysozyme studied by laser flash photolysis and steady-state analysis

Photoprocesses of 1,4-naphthoquinone (NQ) and its photoreactions with lysozyme in acetonitrile/water (3:1, v/v) solution were studied using 355 nm laser flash photolysis technique combined with electrophoresis and turbidimetric assay. The transient spectra of NQ were observed and the transient species were assigned. The electron transfer process from N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) to NQ triplet state (3NQ∗) was investigated and the rate constant was determined to be kt1 = 2.0 × 1010 M−1 s−1. It has been found that 3NQ∗ can abstract hydrogen atom from lysozyme with a rate constant of kt2 = 2.4 × 1010 M−1 s−1. Furthermore, the results of steady-state analysis suggested that lysozyme can be damaged by NQ irradiated with UVA light influenced by the concentration of NQ and the gas saturated in the solution. The mechanisms of photosensitized damage of lysozyme were discussed.