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KMID : 0903519990420010019
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Journal of the Korean Society of Agricultural Chemistry and Biotechnology
1999 Volume.42 No. 1 p.19 ~ p.24
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Effects of Various Calmodulins on the Activation of Glutamate Decarboxylase and Nicotinamide Adenine Dinueleotide Kinase Isolated from Tobacco Plants
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Yun Song-Joong
Oh Suk-Heung
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Abstract
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Plants have been shown to contains Ca^(2+)/calmodulin-stimulated GAD and NAD kinase. To test how calmodulin and calmodulin methylation affect the activation of GAD and NAD kinase, GAD and NAD kinase were partially purified from tobacco plants. GAD was also partially purified from E. coli transformed with a plasmid carrying a cloned tobacco GAD gene. We find that GAD from the transformed E. coli showed 60-fold Ca^(2+)/calmodulin-dependent activation. However, GAD from tobacco plants was stimulated only about 3.8-fold by the addition of calmodulin in the presence of calcium, suggesting high background activity of the enzyme was possibly due to bound endogenous tobacco calmodulin. There were no significant differences in the tobacco GAD activator properties between calmodulins. A monoclonal antibody against petunia GAD interacted strongly with both GAD from tobacco plants and GAD from cloned gene. NAD kinase from tobacco plants showed a complete Ca^(2+)/calmodulin dependency for activity. Unmethylated calmodulins activated GAD in a manner similar to methylated calmodulin. However, the maximum level of NAD kinase activation obtained with unmethylated calmodulins is approximately 4-fold higher than methylated calmodutins. These data suggested that endogenous tobacco calmodulin may interact more tightly with GAD than NAD kinase and that calmodulin methylation affects the activator properties of calmodulins for tobacco NAD kinase but not for GAD.
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