2,3-Diphosphoglycerate is a nonselective inhibitor of inositol 1,4,5-trisphosphate action and metabolism

Inositol 1,4,5-trisphosphate (InsP 3) is an important second messenger generated from the hydrolysis of phosphatidylinositol 4,5-bisphosphate by phospholipase C in response to Ca 2+-mobilizing stimuli. InsP 3 interacts with specific intracellular receptors and triggers the release of sequestered Ca 2+ from an intracellular store. We have looked at the influence of 2,3-diphosphoglycerate on the action and metabolism of InsP 3 in the bovine adrenal cortex. 2,3-Diphosphoglycerate blocked InsP 3 binding to adrenal cortex microsomes with a half-maximal efficiency of 0.5 mM. Scatchard analyses revealed that 2,3-diphosphoglycerate did not change the maximal capacity of the microsomes, but decreased their binding affinity for InsP 3. The Ca 2+-releasing activity of InsP 3 on the same microsomal preparation was monitored with the fluorescent indicator, Fura-2. 2,3-Diphosphoglycerate blocked this activity with a half-maximal efficiency of 2 mM. The effect of 2,3-diphosphoglycerate could be overcome by supramaximal doses of InsP 3, indicating a competitive inhibitory effect. The activity of InsP 3 phosphatase from bocine adrenal cortex microsomes was also studied. 2,3-Diphosphoglycerate inhibited the activity of the phosphatase with a half-maximal efficiency of 0.3 mM. Lineweaver-Burke plots revealed that this effect was competitive. Finally, 2,3-diphosphoglycerate was also able to inhibit the activity of a partially purified preparation of InsP 3 kinase from bovine adrenal cortex cytosol. The half-maximal dose was around 10 mM and the Lineweaver-Burke plot showed that the inhibition was competitive. These results show that 2,3-diphosphoglycerate can be considered as a structural analog of InsP 3. Its inhibitory effects, however, are not selective enough to use it as an InsP 3 protective agent in Ca 2+-mobilization studies.