Inositol phosphate metabolism

Inositol phosphates (IPs) are molecules involves in signalling processes in eukaryotes. myo-Inositol consists of a six-carbon cyclic alcohol with an axial 2-hydroxy and five equatorial hydroxyls. Mono-, di-, and triphosphorylation of the inositol ring generates a wide variety of stereochemically distinct signalling entities. Inositol 1,4,5-trisphosphate (I(1,4,5)P3), is formed when the phosphoinositide phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is hydrolysed by a phospholipase C isozyme. An array of inositol trisphosphate (IP3) and tetrakisphosphate (IP4) molecules are synthesised by the action of various kinases and phosphatases in the cytosol. These species then transport between the cytosol and the nucleus where they are acted on by inositol polyphosphate multikinase (IPMK), inositol-pentakisphosphate 2-kinase (IPPK), inositol hexakisphosphate kinase 1 (IP6K1) and 2 (IP6K2), to produce IP5, IP6, IP7, and IP8 molecules. Some of these nuclear produced IPs transport back to the cytosol where they are converted to an even wider variety of IPs, by kinases and phosphatases, including the di- and triphospho inositol phosphates aka pyrophosphates (Irvine & Schell 2001, Bunney & Katan 2010, Alcazar-Romain & Wente 2008, York 2006, Monserrate and York 2010).

肌醇磷酸盐（IPs）是一类参与真核生物信号传导过程的分子。肌醇（myo-Inositol）由一个六碳环状醇组成，其中包含一个轴向的2-羟基和五个等位的羟基。肌醇环的单、二、三磷酸化过程产生了众多立体化学上独特的信号分子。当磷脂酰肌醇4,5-二磷酸（PI(4,5)P2）被磷脂酶C同工酶水解时，便形成了肌醇1,4,5-三磷酸（I(1,4,5)P3）。通过细胞质中各种激酶和磷酸酶的作用，合成了肌醇三磷酸（IP3）和四磷酸（IP4）分子阵列。这些分子在细胞质与细胞核之间运输，并在肌醇多磷酸激酶（IPMK）、肌醇-五磷酸2-激酶（IPPK）、肌醇六磷酸激酶1（IP6K1）和2（IP6K2）的作用下，转化为肌醇五磷酸（IP5）、肌醇六磷酸（IP6）、肌醇七磷酸（IP7）和肌醇八磷酸（IP8）分子。其中一些在细胞核中产生的IPs返回细胞质，通过激酶和磷酸酶的作用，转化为更为多样的IPs，包括二磷酸和三磷酸肌醇磷酸盐，亦即焦磷酸盐（Irvine & Schell 2001, Bunney & Katan 2010, Alcazar-Romain & Wente 2008, York 2006, Monserrate and York 2010）。