Isolation of a phosphomonoesterase from human platelets that specifically hydrolyzes the 5-phosphate of inositol 1,4,5-trisphosphate.
Year: 1985
Type: article
Abstract: Platelets, and a variety of other cells, rapidly hydrolyze the phosphoinositides in response to stimulation by agonists. One of the products of hydrolysis of phosphatidylinositol 4,5-diphosphate is inositol 1,4,5-trisphosphate, which recently has been suggested to mediate intracellular Ca2+ mobilization. We have found that human platelets contain an enzyme that degrades inositol 1,4,5-trisphosphate. We have isolated this soluble enzyme and find that it hydrolyzes the 5-phosphate of inositol 1,4,5-trisphosphate (Km = 30 microM, Vmax = 5.3 microM/min/mg of protein). The products of the reaction are inositol 1,4-diphosphate and phosphate. The apparent molecular weight of the enzyme is 38,000 as determined both by gel filtration and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence and absence of 2-mercaptoethanol. This enzyme is specific for inositol 1,4,5-trisphosphate. Other water soluble inositol phosphates as well as phosphorylated sugars are not hydrolyzed, while the only inositol containing phospholipid hydrolyzed is phosphatidylinositol 4,5-diphosphate at a rate less than 1% that for inositol 4,5-trisphosphate. The inositol 1,4,5-trisphosphate 5-phosphomonoesterase requires Mg2+ for activity and is inhibited by Ca2+, Ki = 70 microM. Li+, up to 40 mM, has no effect on enzyme activity. The duration and magnitude of any inositol 1,4,5-trisphosphate response in stimulated platelets may be determined by the activity of this enzyme.
Source: Journal of Biological Chemistry
Authors: T M Connolly, T E Bross, P W Majerus
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $3,430
Awards: G1631700890, G266292170
OpenAlex ID: W1480114110