Characterization of ATPases Associated with Various Cellular Membranes Isolated from Etiolated Hypocotyls of Vigna radiata (L.) Wilczek

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Cellular membrane fractions, including endoplasmic reticum (ER), Golgi-enriched membrane, plasma membrane and tonoplasts, were isolated from Vigna radiata seedlings. Each of these membrane fractions was associated with specific ATPases which were highly dependent on Mg^<2+>. ATPases of ER, Golgi-enriched membrane and plasma membrane were sensitive to vanadate but the tonoplast ATPase was not. ATPases were mostly dependent on Cl^-, but a slight stimulation by K^+ was observed in the case of ATPases of Golgi-enriched membrane and plasma membrane. KNO_3 inhibited tonoplast ATPase but stimulated the other ATPases. ER ATPase can be distinguished from other ATPases by the following characteristics: specific inhibi-tion by KNO_2 and Triton X-100, stimulation by low concentrations of diethylstilbestrol and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, and high sensitivity to heat. The ATPases showed typical Michaelis-Menten kinetics and had K_m values of 0.5 to 0.6 mM Mg^<2+>-ATP for ER, Golgi-enriched-membrane and tonoplast ATPases, and 2.27 mM Mg^<2+>-ATP for plasma membrane ATPase. ATPases of Golgi-enriched membranes and plasma membranes had similar properties, but they were still distinguishable by the differences in their K_m values and their responses to Triton X-100. Based on these results, it is postulated that each cellular membrane is associated with a specific ATPase in cells of V. radiata.
日本植物生理学会の論文