title: Effects of medium viscosity on kinetics of the enzymatic reaction catalyzed by bacterial RNase
abstract: 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 degreesC. The rate constant of reaction kcat was practically unchanged over a wide range of viscosities (1-15 cP for sucrose and 2.5-3 cP for glycerol). In glycerol solutions, kcat 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 kcat, 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.
authors.affiliation: Laboratory of Molecular Biophysics, Kazan Institute of Biology, Kazan Research Center, Russian Academy of Sciences, Kazan, 420503, Russia. Stupishina@sci.kcn.ru.
authors.initials: EA
authors.lastname: Stupishina
authors.initials: VI
authors.lastname: Vershinina