title: The effect of pH and various cations on the GTP hydrolysis of rice heterotrimeric G-protein alpha 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 MgCl(2) concentration. The steady state rate constant (k(cat) ) for GTP hydrolysis of RGA1 at 2 mM MgCl(2) 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 MgCl(2) was approximately 6.0; whereas, the pH at 2 mM NH(4)Cl 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(4)Cl at pH 4.0 was the highest. It corresponded to about 3.24-fold of the k(cat) value of 0.0109 min(-1) in the presence of 2 mM MgCl(2) at pH 6.0.
authors.affiliation: Division of Applied Life Sciences, Graduate School of Gyeongsang National University, Jinju 660-701, Korea.
authors.forename: Hak Soo
authors.initials: HS
authors.lastname: Seo
authors.forename: Jin Yong
authors.initials: JY
authors.lastname: Jeong
authors.forename: Min Yeop
authors.initials: MY
authors.lastname: Nahm
authors.forename: Sam Woong
authors.initials: SW
authors.lastname: Kim
authors.forename: Sang Yeol
authors.initials: SY
authors.lastname: Lee
authors.forename: Jeong Dong
authors.initials: JD
authors.lastname: Bahk
mesh_terms: D002412:Cations / Q000494:pharmacology*; D004926:Escherichia coli / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism; D044385:GTP-Binding Protein alpha Subunits / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D012275:Oryza / Q000201:enzymology*
chemical_list: D002412:Cations; D044385:GTP-Binding Protein alpha Subunits; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases