The effect of pH and various cations on the GTP hydrolysis of rice heterotrimeric G-protein alpha subunit expressed in Escherichia coli.
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.
Seo
Hak Soo
HS
Division of Applied Life Sciences, Graduate School of Gyeongsang National University, Jinju 660-701, Korea.
Jeong
Jin Yong
JY
Nahm
Min Yeop
MY
Kim
Sam Woong
SW
Lee
Sang Yeol
SY
Bahk
Jeong Dong
JD
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*
D002412:Cations; D044385:GTP-Binding Protein alpha Subunits; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases