Metabolism of inositol 1,4,5-trisphosphate to higher inositol phosphates in bovine adrenal cytosol.
The metabolism of inositol 1,4,5-trisphosphate to inositol 1,3,4,5-tetrakisphosphate was studied in a cytosolic fraction prepared from the bovine adrenal cortex. The activity of the partially purified inositol 1,4,5-trisphosphate 3-kinase was dependent on Ca2+/calmodulin, Mg2+, and pH, and was inhibited by 2,3-bisphosphoglycerate. The enzyme exhibited Michaelis-Menten behavior toward its two substrates, inositol 1,4,5-trisphosphate and ATP, with Km values of 0.42 mumol/L and 0.4 mmol/L, respectively. The presence of other inositol-phosphate metabolizing enzymes in the cytosolic fraction was indicated by the appearance of additional inositol polyphosphates during prolonged incubation with inositol 1,4,5-trisphosphate. These included inositol 1,3,4-trisphosphate, inositol 1,3,4,6-tetrakisphosphate, and inositol pentakisphosphate. These findings are consistent with the rapid phosphorylation of inositol 1,4,5-trisphosphate to the 1,3,4,5-tetrakisphosphate by the calcium/calmodulin-dependent 3-kinase, and its subsequent conversion to inositol 1,3,4-trisphosphate and thence to inositol 1,3,4,6-tetrakisphosphate in angiotensin-stimulated bovine glomerulosa cells. The formation of inositol pentakisphosphate during prolonged incubations suggests that inositol 1,3,4,6-tetrakisphosphate is slowly phosphorylated and serves as a source of inositol pentakisphosphate in the adrenal. The metabolic conversion of inositol 1,4,5-trisphosphate to several higher inositol polyphosphates provides potential new messengers for intracellular regulation in agonist-stimulated target cells.
Guillemette
G
G
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, Bethesda, MD 20892.
Balla
T
T
Baukal
A J
AJ
Catt
K J
KJ
D019794:2,3-Diphosphoglycerate; D000302:Adrenal Cortex / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D002147:Calmodulin / Q000032:analysis / Q000378:metabolism; D002417:Cattle; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism*; D004163:Diphosphoglyceric Acids / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000096:biosynthesis / Q000378:metabolism*; D007700:Kinetics; D010770:Phosphotransferases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor); D013403:Sugar Phosphates / Q000378:metabolism*; D013997:Time Factors
D002147:Calmodulin; D004163:Diphosphoglyceric Acids; D007295:Inositol Phosphates; D013403:Sugar Phosphates; D019794:2,3-Diphosphoglycerate; D015544:Inositol 1,4,5-Trisphosphate; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; D002118:Calcium