Flavonoids as Effective Protectors of Urease from Ultrasonic Inactivation in Solutions

E. I. Tarun^a, V. P. Kurchenko^b, and D. I. Metelitza^a,#

^# Fax: 375-172-63-7274; e-mail: metelitza@iboch.bas-net.by
^a Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, ul. akademika Kuprevicha, 5/2, Minsk, 220141 Belarus
^b Faculty of Biology, Belarussian State University, ul. Kurchatova 10, Minsk, 220064 Belarus

Received May 31, 2005; in final form, August, 29, 2005

Abstract: Inactivation of soybean urease in aqueous solution at pH 5.4, 36ºC, and high-frequency sonication (2.64 MHz, 1.0 W/cm²) is substantially reduced in the presence of seven structurally different flavonoids. A comparative kinetic study of the effect of these flavonoids on the effective first-order rate constants that characterize the total (thermal and ultrasonic) inactivation k_i, thermal inactivation k*_i, and ultrasonic inactivation k_i(US) of 25 nM enzyme solution was carried out. The dependences of the three inactivation rate constants of the urease on the concentrations of flavonoids within the range from 10^–11 to 10^–4 M were obtained. The following order of the efficiency of the flavonoids used in respect of the urease protection from ultrasonic inactivation was found: astragalin > silybin > naringin > hesperidin > quercetin > kaempferol > morin. The results confirm a significant role in the inactivation of the urease of HO· and HO₂· free radicals, which are formed in the ultrasonic cavitation field.

Key words: flavonoids, free radicals, ultrasound, urease, urease stabilization from inactivation

Russian Journal of Bioorganic Chemistry 2006, 32 (4):352-359