title: Metabolism of inositol 1,4,5-trisphosphate in guinea-pig hepatocytes.
abstract: Metabolism of inositol 1,4,5-trisphosphate was investigated in permeabilized guinea-pig hepatocytes. The conversion of [3H]inositol 1,4,5-trisphosphate to a more polar 3H-labelled compound occurred rapidly and was detected as early as 5 s. This material co-eluted from h.p.l.c. with inositol 1,3,4,5 tetrakis[32P]phosphate and is presumably an inositol tetrakisphosphate. A significant increase in the 3H-labelled material co-eluting from h.p.l.c. with inositol 1,3,4-trisphosphate occurred only after a definite lag period. Incubation of permeabilized hepatocytes with inositol 1,3,4,5-tetrakis[32P]phosphate resulted in the formation of 32P-labelled material that co-eluted with inositol 1,3,4-trisphosphate; no inositol 1,4,5-tris[32P]phosphate was produced, suggesting the action of a 5-phosphomonoesterase. The half-time of hydrolysis of inositol 1,3,4,5-tetrakis[32P]phosphate of approx. 1 min was increased to 3 min by 2,3-bisphosphoglyceric acid. Similarly, the rate of production of material tentatively designed as inositol 1,3,4-tris[32P]phosphate from the tetrakisphosphate was reduced by 10 mM-2,3-bisphosphoglyceric acid. In the absence of ATP there was no conversion of [3H]inositol 1,4,5-trisphosphate to [3H]inositol tetrakisphosphate or to [3H]inositol 1,3,4-trisphosphate, which suggests that the 1,3,4 isomer does not result from isomerization of inositol 1,4,5-trisphosphate. The results of this study suggest that the origin of the 1,3,4 isomer of inositol trisphosphate in isolated hepatocytes is inositol 1,3,4,5-tetrakisphosphate and that inositol 1,4,5-trisphosphate is rapidly converted to this tetrakisphosphate. The ability of 2,3-bisphosphoglyceric acid, an inhibitor of 5-phosphomonoesterase of red blood cell membrane, to inhibit the breakdown of the tetrakisphosphate suggests that the enzyme which removes the 5-phosphate from inositol 1,4,5-trisphosphate may also act to convert the tetrakisphosphate to inositol 1,3,4-trisphosphate. It is not known if the role of inositol 1,4,5-trisphosphate kinase is to inactivate inositol 1,4,5-trisphosphate or whether the tetrakisphosphate product may have a messenger function in the cell.
mesh_terms: D019794:2,3-Diphosphoglycerate; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002469:Cell Separation; D002851:Chromatography, High Pressure Liquid; D004163:Diphosphoglyceric Acids / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007294:Inositol / Q000031:analogs & derivatives / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D013403:Sugar Phosphates / Q000378:metabolism*
chemical_list: D004163:Diphosphoglyceric Acids; D007295:Inositol Phosphates; D013403:Sugar Phosphates; D000804:Angiotensin II; D019794:2,3-Diphosphoglycerate; C013063:inositol hexasulfate; D007294:Inositol; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate