Effects of Medium Viscosity on Kinetics of the Enzymatic Reaction Catalyzed by Bacterial RNase

E. A. Stupishina^1* and V. I. Vershinina²

¹Laboratory of Molecular Biophysics, Kazan Institute of Biology, Kazan Research Center, Russian Academy of Sciences, ul. Lobachevskogo 2/31, P.O. Box 30, Kazan, 420503 Russia; E-mail: Stupishina@sci.kcn.ru

²Department of Microbiology, School of Biology, Kazan State University, ul. Kremlevskaya 18; Kazan, 420008 Russia; fax: (8432) 38-0994; E-mail: Valentina.Vershinina@ksu.ru

^* To whom correspondence should be addressed.

Received January 13, 1998

---

Effects of medium viscosity on kinetic parameters of poly(U) hydrolysis catalyzed by RNase from Bac. intermedius 7P (binase) were studied in solutions of sucrose (4-50 wt. %) and glycerol (35-62 wt. %) in Tris--sodium acetate buffer (pH 7.5) at 25°C. The rate constant of reaction k_cat was practically unchanged over a wide range of viscosities (1-15 cP for sucrose and 2.5-3 cP for glycerol). In glycerol solutions, k_cat slightly increased with viscosity increase from 4 to 10 cP. Addition of NaCl to the buffer medium resulted in an inhibitory effect of Na⁺ on k_cat, prevented by 50% sucrose or 60% glycerol. It is concluded that binase-catalyzed poly(U) cleavage occurs through a “tense”-substrate mechanism, similarly to reactions catalyzed by alpha-chymotrypsin, trypsin, and laccase.

---

KEY WORDS: RNase from Bac. intermedius 7P, enzymatic catalysis, medium viscosity, kinetic parameters

---