Phosphatidylinositol-cleaving activity in smooth muscle from rat vas deferens |
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Affiliation: | 2. Department of Neurology, Akershus University Hospital, Lørenskog, Norway;3. Institute of Clinical Medicine, University of Oslo, Oslo, Norway;4. Centre for Connected Care, Oslo University Hospital, Oslo, Norway |
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Abstract: | - 1.1. Phosphatidylinositol-cleaving activity was studied in subcellular fractions from smooth muscle of rat vas deferens.
- 2.2. In the presence of calcium ions and deoxycholate most of the endogenous phosphatidylinositol was broken-down in 60 min, whilst the other phospholipids were stable.
- 3.3. The enzymatic activity responsible for this breakdown catalyses a phospholipase C-type cleavage of the glycerol-phosphate bond, the water soluble products from exogenous [32P]-labelled phosphatidylinositol being d-myoinositol 1:2-cyclic phosphate (702-80%) and d-myoinositol 1-phosphate (202-30%).
- 4.4. Activity was abolished by 1 mM ethanedioxybis(ethylamine)tetra-acetate (EGTA) and in the presence of deoxycholate both the soluble and total particulate fractions showed maximum activity at pH 6.52-6.8. The soluble fraction showed a second peak of activity at pH 5.52-5.8 that was independent of deoxycholate; this was not observed in the particulate fraction.
- 5.5. About two-thirds of the activity was soluble. The remaining activity was particulate, with a preferential concentration in the microsomal fraction.
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