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KMID : 0903519970400030202
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Journal of the Korean Society of Agricultural Chemistry and Biotechnology
1997 Volume.40 No. 3 p.202 ~ p.208
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Ca2+ induced Inhibition of Microsomal ATPases in Soybean Roots
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김영기/Kim, Young Kee
조경수/조광현/이은형/Cho, Kyoung Soo/Cho, Kwang Hyun/Lee, Eun Hyoung
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Abstract
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In order to investigate the mechanisms of epithelial ion transports, microsomes of soybean roots were prepared and the activity of microsomal ATPases was measured by an enzyme-coupled assay. The effects of various ions were evaluated on the total activity of microsomal ATPases and the average activity was 190 nmol/min/㎎ protein in the control solution containing 10 mM Na^+ and 120 mM K^+. The activities were increased to 150% and decreased to 63% of the control activity in the solution containing 130 mM K^+ without Na^+ and in the solution containing 130 mM Na^+ without K^+, respectively. In general, the activity of microsomal ATPase was increased by K^+ in a concentration-dependent manner. The activity was also increased at lower pH and relatively higher activities were observed in the pH range of 6∼7. However, the activity was decreased at weak alkaline pH and ∼80% of the activity was inhibited at pH 9. Since intracellular Ca^(2+) has been known to control the activity of various enzymes, we have investigated the effects of intra- and extramicrosomal Ca^(2+) on the activity of microsomal ATPases. The maximal activity was obtained at the extramicrosomal Ca^(2+) concentrations below 1 nM. The activity was gradually decreased by increasing Ca^(2+) concentration and 50% inhibition was observed at ∼500 μM Ca^(2+). The increase in luminal Ca^(2+) concentration also inhibited the activity of microsomal ATPase. When the influx of external Ca^(2+) was induced by Ca^(2+) ionophore A23187 treatment, the activity was decreased by 30%; however, it was recovered by EGTA-induced chelation of Ca^(2+). These results suggest that the presence of Ca^(2+) regulation sites on both cytoplasmic and luminal sides of microsomal ATPases.
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