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Seo, Hak-Soo,Jeong, Jin-Yong,Nahm, Min-Yeop,Kim, Sam-Woong,Lee, Sang-Yeol,Bahk, Jeong-Dong Korean Society for Biochemistry and Molecular Biol 2003 Journal of biochemistry and molecular biology Vol.36 No.2
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 $0.0075{\pm}0.0001\;min^{-1}$. 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 $NH_4Cl$ 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 2mM $NH_4Cl$ 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.
( Hak Soo Seo ),( Jin Yong Jeong ),( Min Yeop Nahm ),( Sam Woong Kim ),( Sang Yeol Lee ),( Jeong Dong Bahk ) 생화학분자생물학회 2003 BMB Reports Vol.36 No.2
Previously, we reported the biochemical properties of RGAl that is expressed in Escherichia coli(Seo et al., 1997). The activities of RGAl that hydrolyzes and binds guanine nucleotide were dependent on the MgCl_(2) concentration. The steady state rate constant (k_(cat)) for GTP hydrolysis of RGAl 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 2mM 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 RGAl under the same condition showed that the GTP hydrolysis rate (k_(cat)=0.0353 min^(-1)) under the condition of 2mM 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 2mM MgCl_(2) at pH 6.0.
A rac-like small G-protein from Brassica campestris activates a PKC-dependent phospholipase D
Kim, Ho-yeon,Nahm, Min-yeop,Lim, Chae-oh,Yun, Dae-jin,Cho Moo-je,Bahk, Jeong-dong Plant molecular biology and biotechnology research 2004 Plant molecular biology and biotechnology research Vol.2004 No.-
A cDNA clone encoding a rac-like small GTP binding protein was isolated from a cDNA library of Chinese cabbage (Brassica campestris L. ssp. pekinensis) flower buds and named Brac1. The Brac1 cDNA contains an open reading frame encoding 198 amino acid residues with an estimated molecular mass of 21.690 Da and this coding region has conserved residues and motifs unique to the Rho subfamily of proteins. The deduced amino acid sequence of the Brac1 protein is closely related to that of Arabidopsis thaliana Arac3 (91%), but it shares relatively little homology with other members of the Ras superfamily (about 30% identity). To further characterize Brac1, a pGBrac1 expression vector consisting of PCR-amplified Brac1 cDNA plus glutathione S-transferase (GST) and pBKS(+)Ⅱ was used to purify the protein. Using a PEI-cellulose/TLC plate, GTPase activity of this protein was confirmed and competition binding studies, using the guanine nucleotides, ATP, UTP and CTP, revealed that the di- and triphosphate forms of guanine nucleotides strongly bind Brac1. Membrane-bound PLD activity was synergistically enhanced by Brac1 in he presence of protein kinase C, but not in the presence of ARF (ADP-ribosylation factor). Genomic analysis indicated that brac1 belongs to a multigene family. Brac1 transcripts were expressed in all the organs of Brassica, but were especially prevalent in flower buds.