Promotion of β-Glucan Synthase Activity in Corn Microsomal Membranes by Calcium and Protein Phosphorylation

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概要

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• Regulation of the activity of β-glucan synthase was studied using microsomal preparations from corn coleoptiles. The specific activity as measured by the incorporation of glucose from uridine diphospho-D-[U-^<14>C]glucose varied between 5 to 15 pmol・(mg protein)^<-1>・min^<-1>. Calcium promoted β-glucan synthase activity and the promotion was observed at free calcium concentrations as low as 1μM. Kinetic analysis of substrate-velocity curve showed an apparent K_m of 1.92×10^<-4>M for UDPG. Calcium increased the V_<max> from 5.88×10^<-7> mol・liter^<-1>・min^<-1> in the absence of calcium to 9.52×10^<-7> mol ・liter^<-1>・min^<-1> and 1 .66×10^<-6> mol・liter^<-1>・min^<-1> in the presence of 0.5 mM and 1 mM calcium, respectively. The K_m values remained the same under these conditions. Addition of ATP further increased the activity above the calcium-promoted level. Sodium fluoride, a phosphoprotein phosphatase inhibitor, promoted glucan synthase activity indicating that phosphorylation and dephosphorylation are involved in the regulation of the enzyme activity. Increasing the concentration of sodium fluoride from 0.25 mM to 10mM increased glucan synthase activity five-fold over the+calcium+ATP control. Phosphorylation of membrane proteins also showed a similar increase under these conditions. Calmodulin, in the presence of calcium and ATP stimulated glucan synthase activity substantially, indicating that calmodulin could be involved in the calcium-dependent phosphorylation and promotion of β-glucan synthase activity. The role of calcium in mediating auxin action is discussed.

• 日本植物生理学会の論文

著者

• Poovaiah B.

  Laboratory Of Plant Molecular Biology And Physiology Department Of Horticulture And Landscape Archit

• Poovaiah B.

  Laboratory Of Plant Molecular Biology And Physiology Department Of Horticulture And Landscape Archit

• Paliyath G.

  Laboratory of Plant Molecular Biology and Physiology, Department of Horticulture and Landscape Archi

• Paliyath G.

  Laboratory Of Plant Molecular Biology And Physiology Department Of Horticulture And Landscape Archit

関連論文

• Auxin-Induced Changes in Protein Synthesis in the Abscission Zone of Bean Explants
• Effect of Calcium on Cell Wall Structure, Protein Phosphorylation and Protein Profile in Senescing Apples
• The Effect of Calcium Antagonists on Auxin-induced Elongation and on the Expression of Two Auxin-Regulated Genes in Pea Epicotyls
• Calcium and Protein Phosphorylation in the Transduction of Gravity Signal in Corn Roots
• Promotion of β-Glucan Synthase Activity in Corn Microsomal Membranes by Calcium and Protein Phosphorylation

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