Inhibition of Microsomal $H^+\;-\;ATPase$ Prepared from Tomato Roots by Various Anions

음이온에 의한 토마토 뿌리조직 마이크로솜 $H^+-ATPase$ 활성 저해

$H^+-ATPase$ located on plasma and vacuolar membranes play major roles in various cellular physiological processes. In order to investigate the physiological roles of $H^+-ATPase$, microsomes were prepared from tomato roots and the effects of various anions were measured on the activities of $H^+-ATPase$. $H^+-ATPase$ was inhibited by various anions. Citrate and phosphate were chosen to investigate detailed inhibitory mechanisms on $H^+-ATPase$ since they showed different levels of inhibition. Inhibitory effect of citrate was observed at the concentrations above 3 mM. When 20 mM citrate was added, the ATPase activity was decreased by 50-60%. However, the inhibitory effect of citrate was decreased by increasing the concentration of$Mg^{2+}$ The citrate-induced inhibited activity was recovered by the addition of $Mg^{2+}$ Addition of 7 mM $Mg^{2+}$ completely removed the inhibitory effect of citrate and the activity recovered to the level of the control experiment. These results imply that citrate chelates $Mg^{2+}$ and thus inhibits $H^+-ATPase$. Meanwhile, the inhibitory effect of phosphate was observed at the concentration above 3 mM and the activity was decreased by 50% in the presence of 30 mM phosphate. Further addition of $Mg^{2+}$ showed no recovery on the activity. These results imply that the inhibitory effect of phosphate is not dependent upon the concentration of $Mg^{2+}$.

식물 뿌리세포의 원형질막 및 액포막에 위치하는 $H^+-ATPase$들은 세포의 여러 가지 생리활성에 중요한 역할을 수행한다. $H^+-ATPase$의 생리활성 특성을 조사하기 위하여 토마토 뿌리조직으로부터 마이크로솜을 분리하고, $H^+-ATPase$의 활성에 미치는 음이온의 효과를 조사하였다. 다양한 종류의 음이온들이 $H^+-ATPase$의 활성을 저해함을 확인하였으며, 이들 중 특히 효소의 저해정도가 다른 citrate와 인산을 선택하여 작용특성을 조사하였다. Citrate에 의한 ATPase활성저해는 3 mM 이상에서 나타났고, 20 mM citrate는 활성을 50-60% 저해하였다. 그러나, citrate의 저해효과는 $Mg^{2+}$의 농도를 증가시킬수록 감소하여, citrate에 의해 저해된 ATPase 활성은 $Mg^{2+}$에 의해 회복되는 것으로 나타났다. 즉, 7 mM $Mg^{2+}$을 첨가하였을 때, citrate에 의한 활성저해는 관측되지 않았고 ATPase활성은 대조활성과 비슷한 수준으로 회복되었다. 이러한 결과로 부터 citrate는 Mg^{2+}을 chelation함으로써$H^+-ATPase$의 활성을 저해함을 확인하였다. 한편, 인산에 의한 ATPase활성저해는 3 mM 이상의 농도에서 나타났고, 30 mM 인산은 ATPase의 활성을 50% 저해하였다. 인산에 의해서 저해된 ATPase의 활성은 $Mg^{2+}$니 농도증가에 의해 회복되지 않아, 인산에 의한 저해효과는 $Mg^{2+}$과 무관하였다.