Calcium transport and ATPase activity in a microsomal vesicle fraction from corn roots |
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Authors: | GRAZIANO ZOCCHI JOHN B HANSON |
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Institution: | Department of Botany, University of Illinois, Urbana, Illinois 61801, U.S.A. |
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Abstract: | Abstract. An investigation has been made of methods for isolating membrane vesicles from corn ( Zea mays L.) roots active in calcium transport and K+-stimulated ATPase. Pretreating and grinding the roots at room temperature with EGTA and fusicoccin increases basal ATPase activity. Improvement in Ca2+ uptake requires isolation of a scaled vesicle fraction by the method of Sze(1980). Sorbitol is superior to sucrose as an osmoticant. The pH optimum for Ca2+ uptake is 7.5. whereas that for associated ATPase activity is 6.5. Calmodulin strongly stimulates Ca2+ uptake in a process little affected by uncouplers and ATPase inhibitors, but blocked by chlorpromazine. Fusicoccin gives less stimulation of Ca2+ uptake which is sensitive to uncouplers, and is dependent upon isolation with fusicoccin present. It appears that the sealed vesicle fraction may possess two Ca2+ transport systems: a calmodulin-activated Ca2+-transporting ATPase, and a Ca2+/H+ antiport coupled through the protonmotive force to a fusicoccin-stimulated H+-ATPase. |
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Keywords: | Zea mays ATPase Ca2+ transport calmodulin fusicoccin |
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