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Metabolism and Enzymology

Inositol Trisphosphate Metabolism in Carrot (Daucus carota L.) Cells ¹

Department of Botany, Box 7612, North Carolina State University Raleigh, North Carolina 27695

The metabolism of exogenously added D-myo-[1-³H]inositol 1,4,5-trisphosphate (IP₃) has been examined in microsomal membrane and soluble fractions of carrot (Daucus carota L.) cells grown in suspension culture. When [³H]IP₃ was added to a microsomal membrane fraction, [³H]IP₂ was the primary metabolite consisting of approximately 83% of the total recovered [³H] by paper electrophoresis. [³H]IP was only 6% of the [³H] recovered, and 10% of the [³H]IP₃ was not further metabolized. In contrast, when [³H]IP₃ was added to the soluble fraction, approximately equal amounts of [³H]IP₂ and [³H]IP were recovered. Ca²⁺ (100 micromolar) tended to enhance IP₃ dephosphorylation but inhibited the IP₂ dephosphorylation in the soluble fraction by about 20%. MoO₄^2– (1 millimolar) inhibited the dephosphorylation of IP₃ by the microsomal fraction and the dephosphorylation of IP₂ by the soluble fraction. MoO₄^2–, however, did not inhibit the dephosphorylation of IP₃ by the soluble fraction. Li⁺ (10 and 50 millimolar) had no effect on IP₃ metabolism in either the soluble or membrane fraction; however, Li⁺ (50 millimolar) inhibited IP₂ dephosphorylation in the soluble fraction about 25%.

³ Present address: Noble Foundation, P. O. Box 2180, Ardmore, OK 73402.

¹ Supported by grant No. DE-FG05-87ER 13693 from the U.S. Department of Energy. Paper No. 12229 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601.

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