Cunha-Melo J R, Dean N M, Ali H, Beaven M A
Laboratory of Chemical Pharmacology, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
J Biol Chem. 1988 Oct 5;263(28):14245-50.
Previous studies with antigen-stimulated rat basophilic leukemia (RBL-2H3) cells indicated the formation of multiple isomers of each of the various categories of inositol phosphates. The identities of the different isomers have been elucidated by selective labeling of [3H]inositol 1,3,4,5-tetrakisphosphate with [32P]phosphate in the 3'-or 4',5'-positions and by following the metabolism of different radiolabeled inositol phosphates in extracts of RBL-2H3 cells. We report here that inositol 1,3,4,5-tetrakisphosphate, when incubated with the membrane fraction of extracts of RBL-2H3 cells, was converted to inositol 1,4,5-trisphosphate and inositol 1,3,4-trisphosphate. Further dephosphorylation of the inositol polyphosphates proceeded rapidly in whole extracts of cells, although the process was significantly retarded when ATP (2 mM) levels were maintained by an ATP-regenerating system. The degradation of inositol 1,4,5-trisphosphate proceeded with the sequential formation of inositol 1,4-bisphosphate, the inositol 4-monophosphate (with smaller amounts of the 1-monophosphate), and finally inositol. Inositol 1,3,4-trisphosphate, on the other hand, was converted to inositol 1,3-bisphosphate and inositol 3,4-bisphosphate and subsequently to inositol 4-monophosphate and inositol 1-monophosphate (stereoisomeric forms were undetermined). The possible implications of the apparent interconversion between inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in regulating histamine secretion in the RBL-2H3 cells are discussed.
先前针对抗原刺激的大鼠嗜碱性白血病（RBL - 2H3）细胞开展的研究表明，各类肌醇磷酸酯均会形成多种异构体。通过用[32P]磷酸盐对3'-或4',5'-位的[3H]肌醇1,3,4,5 - 四磷酸进行选择性标记，并追踪RBL - 2H3细胞提取物中不同放射性标记的肌醇磷酸酯的代谢情况，已阐明了不同异构体的身份。我们在此报告，当肌醇1,3,4,5 - 四磷酸与RBL - 2H3细胞提取物的膜部分一起孵育时，会转化为肌醇1,4,5 - 三磷酸和肌醇1,3,4 - 三磷酸。肌醇多磷酸的进一步去磷酸化在细胞的全提取物中迅速进行，不过当通过ATP再生系统维持ATP（2 mM）水平时，该过程会显著减慢。肌醇1,4,5 - 三磷酸的降解过程依次形成肌醇1,4 - 二磷酸、肌醇4 - 单磷酸（还有少量的1 - 单磷酸），最终形成肌醇。另一方面，肌醇1,3,4 - 三磷酸会转化为肌醇1,3 - 二磷酸和肌醇3,4 - 二磷酸，随后再转化为肌醇4 - 单磷酸和肌醇1 - 单磷酸（立体异构体形式未确定）。本文讨论了肌醇1,4,5 - 三磷酸和肌醇1,3,4,5 - 四磷酸之间明显的相互转化在调节RBL - 2H3细胞中组胺分泌方面可能的意义。
