Inhorn R C, Bansal V S, Majerus P W
Proc Natl Acad Sci U S A. 1987 Apr;84(8):2170-4. doi: 10.1073/pnas.84.8.2170.
We prepared [3H]inositol-,3-[32P]phosphate-and 4-[32P]phosphate-labeled inositol phosphate substrates to investigate the metabolism of inositol 1,3,4-trisphosphate and inositol 1,4-bisphosphate. In crude extracts of calf brain, inositol 1,3,4-trisphosphate is first converted to inositol 3,4-bisphosphate, then the inositol 3,4-bisphosphate intermediate is further converted to inositol 3-phosphate. Similarly, inositol 1,4-bisphosphate is converted to inositol 4-phosphate, and no inositol 1-phosphate is formed. We partially purified an enzyme that we tentatively name inositol polyphosphate 1-phosphatase. This cytosolic enzyme converts inositol 1,3,4-trisphosphate to inositol 3,4-bisphosphate and also converts inositol 1,4-bisphosphate to inositol 4-phosphate. The enzyme does not utilize inositol 1,3,4,5-tetrakisphosphate, inositol 1,4,5-trisphosphate, or inositol 1-phosphate as substrates. Thus we propose a new scheme for inositol phosphate metabolism. According to this pathway inositol 1,4,5-trisphosphate and inositol 1,4-bisphosphate are degraded to inositol 4-phosphate. Inositol 1-phosphate, which is the major inositol monophosphate formed in stimulated brain, is derived either from phospholipase C cleavage of phosphatidylinositol or from the degradation of inositol cyclic phosphates.
我们制备了[3H]肌醇、3-[32P]磷酸酯和4-[32P]磷酸酯标记的肌醇磷酸底物，以研究1,3,4-三磷酸肌醇和1,4-二磷酸肌醇的代谢。在小牛脑的粗提物中，1,3,4-三磷酸肌醇首先转化为3,4-二磷酸肌醇，然后3,4-二磷酸肌醇中间体进一步转化为3-磷酸肌醇。同样，1,4-二磷酸肌醇转化为4-磷酸肌醇，未形成1-磷酸肌醇。我们部分纯化了一种酶，暂命名为肌醇多磷酸1-磷酸酶。这种胞质酶将1,3,4-三磷酸肌醇转化为3,4-二磷酸肌醇，也将1,4-二磷酸肌醇转化为4-磷酸肌醇。该酶不利用1,3,4,5-四磷酸肌醇、1,4,5-三磷酸肌醇或1-磷酸肌醇作为底物。因此，我们提出了一种新的肌醇磷酸代谢方案。根据该途径，1,4,5-三磷酸肌醇和1,4-二磷酸肌醇降解为4-磷酸肌醇。1-磷酸肌醇是刺激大脑中形成的主要肌醇单磷酸，它要么来自磷脂酰肌醇的磷脂酶C裂解，要么来自肌醇环磷酸酯的降解。
