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Calcium ion과 ATP에 의해 기질선택성이 조절될 수 있는 Phosphatidylinositol-specific phospholipase C에 대한 연구
황재택,이종호,이영식,이서구,조기승,Hwang, J.T.,Lee, J.H.,Lee, Y.S.,Rhee, S.G.,Cho, K.S. 생화학분자생물학회 1988 한국생화학회지 Vol.21 No.4
생쥐 뇌의 세포질 분획에서 추출한 Phosphatidylinositol-Specific Phospholipase C (PI-PLC, EC 3.1.4.16)를 $^3H$-Phosphatidylinositol ($^3H-PI$)과 $^3H$-Phosphatidylinositol-4.5-bisphosphate ($^3H-PIP_2$)를 기질로 하여 최적 pH 5.0과 생리적 pH 7.2에서 활성도를 보았을 때, 이 효소의 기질선택성이 $Ca^{2+}$ 농도와 ATP 농도에 의해 조절될 수 있음을 나타냈다. $Ca^{2+}$이 존재하지 않은 상태의 pH 5.0과 pH 7.2에서 $PIP_2$는 PI보다 각각 약 4배와 8배의 가수분해도를 나타냈고, 이 조건에서 PI 가수분해는 매우 낮았다. $Ca^{2+}$ 농도를 증가시켰을 때 PI의 가수분해도 pH 5.0과 pH 7.2에서 모두 5 mM까지 계속 증가하는 양상을 보였으나, $PIP_2$ 기질은 pH 5.0에서 $Ca^{2+}$ 농도 1 mM까지 약간 증가하다가 그 이상의 농도에서는 감소현상을 나타냈으며, pH 7.2에서는 0.2 mM까지 증가하다가 그 이상의 농도에서는 급격히 감소되는 결과를 나타냈다. 생리적 pH 7.2에서 ATP에 대한 영향을 보았을 때, PI 기질은 $Ca^{2+}$이 존재하지 않은 경우 아무런 영향이 없었으나 1mM $Ca^{2+}$ 존재하에서는 ATP $10^{-5}M$ 이상의 농도에서 급격히 감소하였다. 한편 $PIP_2$ 기질의 경우, $Ca^{2+}$이 존재 하지 않은 상태에서는 $10^{-3}M$ ATP에 의해 약 100%의 가수분해 증가를 나타냈고, 1 mM $Ca^{2+}$ 존재하에서는 $10^{-2}M$ ATP에 의해 약 150 %의 증가를 나타냈다. Previously reported mouse brain cytosolic PI-phospholipase C (Kim et al., 1987) showed the selectivity of substrates, such as, $^3H-PI$ and $^3H-PIP_2$ was possibly regulated by the concentration of $Ca^{2+}$ and ATP at the optimum pH 5.0 and physiological pH 7.2. The enzymatic hydrolysis of $PIP_2$ at pH 5.0 and pH 7.2 without $Ca^{2+}$ represented about 4 and 8 times higher than PI, respectively. In this condition, PI showed very low hydrolysis. As increase the $Ca^{2+}$ concentrations, the hydrolysis of PI at both pH 5.0 and pH 7.2 showed steady increase until 5 mM $Ca^{2+}$ concentration. On the other hand, the hydrolysis of $PIP_2$ at pH 5.0 showed a little increase until 1 mM $Ca^{2+}$ concentration and decreased after that. And also, the similar result was obtained at pH 7.2 with 0.2 mM $Ca^{2+}$ concentration. In the effect of A TP on the hydrolysis of PI and $PIP_2$ at the physiological pH 7.2, PI hydrolysis was not affected at all without $Ca^{2+}$, but it was significantly decreased over $10^{-5}M$ATP concentration with 1 mM $Ca^{2+}$. In the case of $PIP_2$ ATP showed 100% stimulation with $10^{-3}$M ATP in the absence of $Ca^{2+}$, and 150 % with $10^{-2}M ATP in the presence of 1 mM $Ca^{2+}$, respectively.
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Calcium ion과 ATP 에 의해 기질선택성이 조절될 수 있는 Phosphatidylinositol - specific phospholipase C 에 대한 연구
황재택,이종호,이영식,이서구,조기승 ( J . T . Hwang,J . H . Lee,Y . S . Lee,S . G . Rhee,K . S . Cho ) 생화학분자생물학회 1988 BMB Reports Vol.21 No.4
Previously reported mouse brain cytosolic PI-phospholipase C (Kim et at., 1987) showed the selectivity of substrates, such as, ³H-PI and ³H-PIP₂ was possibly regulated by the concentration of Ca^(2+) and ATP at the optimum pH 5.0 and physiological pH 7.2. The enzymatic hydrolysis of PIP₂ at pH 5.0 and pH 7.2 without Ca^(2+) represented about 4 and 8 times higher than PI, respectively. In this condition, PI showed very low hydrolysis. As increase the Ca^(2+) concentrations, the hydrolysis of PI at both pH 5.0 and pH 7.2 showed steady increase until 5 mM Ca^(2+) concentration. On the other hand, the hydrolysis of PIP₂ at pH 5.0 showed a little increase until 1 mM Ca^(2+) concentration and decreased after that. And also, the similar result was obtained at pH 7.2 with 0.2 mM Ca^(2+) concentration. In the effect of ATP on the hydrolysis of PI and PIP₂ at the physiological pH 7.2, PI hydrolysis was not affected at all without Ca^(2+), but it was significantly decreased over 10^(-5)M ATP concentration with 1 mM Ca^(2+). In the case of PIP₂ATP showed 100% stimulation with 10^(-3)M ATP in the absence of Ca^(2+), and 150 % with 10^(-2)M ATP in the presence of 1 mM Ca^(2+), respectively.
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생쥐 뇌조직에서 부분정제한 Phosphatidylinositol - Specific Phospholipase C Ⅰ과 Ⅱ의 특성
이종호,황재택,김명년,이영식,조기승 ( J . H . Lee,J . T . Hwang,M . N . Kim,Y . S . Lee,K . S . Cho ) 생화학분자생물학회 1991 BMB Reports Vol.24 No.3
Two forms of phosphatidylinositol-specific phospholipase C (PLC-I and PLC-II) were partially purified from mouse brain cytosolic fraction. These enzymes showed optimum pH 5.0 with PI and pH 5.2 with PIP₂ as substrates, respectively. The enzymatic hydrolysis of PI by both isozymes at pH 5.0 and pH 7.2 showed significant increase with increased concentration of Ca^(2+). On the other hand, the hydrolysis of PIP₂ by PLC-I and PLC-II at both pH exhibited the maximum activity in the presence of 0.5 mM and 0.2 mM Ca^(2+), respectively, while inhibited significantly by increasing the concentration of Ca^(2+). Especially without Ca^(2+) at pH 7.2, PIP₂ hydrolysis by PLC-I and PLC-II represented 15 and 4 times higher than those of PI substrate, respectively. From these results, it could be concluded that PIP₂ hydrolysis Ca^(2+) -independent under the same conditions. In the effect of nucleotides on PI hydrolysis at pH 5.0, ATP and GTP inhibited the enzyme activity of both enzymes, but PIP₂ hydrolysis at physiological pH 7.2 by PLC-I and PLC-II enhenced significantly without Ca^(2+). At this condition, 1 mM Ca^(2+) showed no effect at all on the enzyme activity. The results of complete inhibition of the enzyme activity by Ag^+ and Hg^(2+) suggested that -SH group was involved in the active site of both isozymes.
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