Two dephosphorylation pathways of inositol 1,4,5-trisphosphate in homogenates of the cellular slime mould Dictyostelium discoideum.
Two dephosphorylation pathways of inositol 1,4,5-trisphosphate in homogenates of the cellular slime mould Dictyostelium discoideum.
复制标题
细胞粘菌盘基网柄菌匀浆中肌醇 1,4,5-三磷酸的两种去磷酸化途径。
作者：
M. V. L. Campagne;Cristophe Erneux;R. V. Eijk;P. V. Haastert
盘基网柄菌匀浆含有磷酸酶活性，可将Ins（1，4，5）P3（D-肌醇1，4，5-三磷酸盐）快速脱磷酸化为Ins（肌醇）。当在Mg 2+中测定时，Ins（1，4，5）P3被可溶性网骨藻细胞级分去磷酸化为20%Ins（1，4）P2（D-肌-肌醇1，4-二磷酸）和80%Ins（4，5）P2（D-肌-肌醇4，5-二磷酸）。在颗粒组分中，Ins（1，4，5）P35-磷酸酶比Ins（1，4，5）P31-磷酸酶相对更有活性。CaCl_2仅能代替MgCl_2对Ins（1，4，5）P_35-磷酸酶活性起作用。Ins（1，4）P2和Ins（4，5）P2均进一步去磷酸化为Ins 4P Li+离子抑制Ins（1，4，5）P3 1-磷酸酶、Ins（1，4）P2 1-磷酸酶、Ins 4P磷酸酶和L-Ins 1 P（L-肌肌醇1-单磷酸）磷酸酶活性; Ins（1，4，5）P3 1-磷酸酶对Li+的敏感性高10倍25 mM时的半最大抑制）比其它磷酸酶（在约2.5 mM时的半最大抑制）。Ins（1，4，5）P3 5-磷酸酶活性可被2，3-二磷酸甘油酸有效抑制（在3 μ M时达到半数最大抑制）。此外，2，3-二磷酸甘油酸还抑制Ins（4，5）P2的去磷酸化。这些特征表明了网囊藻磷酸肌醇磷酸酶与高等生物磷酸肌醇磷酸酶之间的许多相似之处。然而，迄今为止未描述的Ins（1，4，5）P3 1-磷酸酶的存在导致形成不同于在高等生物中发现的[Ins（1，4）P2]的肌醇二磷酸酶异构体[Ins（4，5）P2]。这些磷酸酶中的一些对Li+的高敏感性表明，它们可能是Li+在网骨藻中改变细胞模式的过程中的靶点。
Dictyostelium discoideum homogenates contain phosphatase activity which rapidly dephosphorylates Ins(1,4,5)P3 (D-myo-inositol 1,4,5-trisphosphate) to Ins (myo-inositol). When assayed in Mg2+, Ins(1,4,5)P3 is dephosphorylated by the soluble Dictyostelium cell fraction to 20% Ins(1,4)P2 (D-myo-inositol 1,4-bisphosphate) and 80% Ins(4,5)P2 (D-myo-inositol 4,5-bisphosphate). In the particulate fraction Ins(1,4,5)P3 5-phosphatase is relatively more active than the Ins(1,4,5)P3 1-phosphatase. CaCl2 can replace MgCl2 only for the Ins(1,4,5)P3 5-phosphatase activity. Ins(1,4)P2 and Ins(4,5)P2 are both further dephosphorylated to Ins4P (D-myo-inositol 4-monophosphate), and ultimately to Ins. Li+ ions inhibit Ins(1,4,5)P3 1-phosphatase, Ins(1,4)P2 1-phosphatase, Ins4P phosphatase and L-Ins1P (L-myo-inositol 1-monophosphate) phosphatase activities; Ins(1,4,5)P3 1-phosphatase is 10-fold more sensitive to Li+ (half-maximal inhibition at about 0.25 mM) than are the other phosphatases (half-maximal inhibition at about 2.5 mM). Ins(1,4,5)P3 5-phosphatase activity is potently inhibited by 2,3-bisphosphoglycerate (half-maximal inhibition at 3 microM). Furthermore, 2,3-bisphosphoglycerate also inhibits dephosphorylation of Ins(4,5)P2. These characteristics point to a number of similarities between Dictyostelium phospho-inositol phosphatases and those from higher organisms. The presence of an hitherto undescribed Ins(1,4,5)P3 1-phosphatase, however, causes the formation of a different inositol bisphosphatase isomer [Ins(4,5)P2] from that found in higher organisms [Ins(1,4)P2]. The high sensitivity of some of these phosphatases for Li+ suggests that they may be the targets for Li+ during the alteration of cell pattern by Li+ in Dictyostelium.