The effect of pH and various cations on the GTP hydrolysis of rice heterotrimeric G-protein α subunit expressed in Escherichia coli

Abstract

Previously, we reported the biochemical properties of RGA1 that is expressed in Escherichia coli (Seo et al., 1997). The activities of RGA1 that hydrolyzes and binds guanine nucleotide were dependent on the MgCl2 concentration. The steady state rate constant (kcat) for GTP hydrolysis of RGA1 at 2 mM MgCl2 was 0.0075 ± 0.0001 min -1. Here, we examined the effects of pH and cations on the GTPase activity. The optimum pH at 2 mM MgCl2 was approximately 6.0; whereas, the pH at 2 mM NH4Cl was approximately 4.0. The result from the cation dependence on the GTPase (guanosine 5′-triphosphatase) activity of RGA1 under the same condition showed that the GTP hydrolysis rate (k cat= 0.0353 min-1) under the condition of 2 mM NH 4Cl at pH 4.0 was the highest. It corresponded to about 3.24-fold of the kcat value of 0.0109 min-1 in the presence of 2 mM MgCl2 at pH 6.0. © KSBMB & Springer-Verlag 2003.