Flavonoids as Effective Protectors of Urease from Ultrasonic Inactivation in Solutions

E. I. Taruna, V. P. Kurchenkob, and D. I. Metelitzaa,#

# 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 ki, thermal inactivation k*i, and ultrasonic inactivation ki(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