Abstract
1. 1. CDP-diacyl- sn-glycerol:inositoltransferase(E.C. 2.7.8.11) which catalyzes the final reaction in de novo synthesis of phosphatidylinositol (PI) is located in the microsomal fraction of bovine mammary tissue and showed specific activities ranging from 2 to 9 nmoles PI formed/mg protein per min. 2. 2. Optimum pH was between 8.5 and 9.0 with CDP-diacyl- sn-glycerol (CDPDG) and 7.7 when CTP and phosphatidic acid were the source of substrate CDPDG. 3. 3. CDP-didecanoyl- sn-glycerol was the preferred substrate with CDP-dioleyl- and CDP-dipalmityl- sn-glycerol showing lower rates of PI synthesis. 4. 4. Apparent K m values of 60 μM and 0.71 mM were obtained for CDP-didecanoyl- sn-glycerol and myoinositol, respectively. 5. 5. Manganese, at 3 mM, was required for activity though magnesium at very high concentrations. 48 mM, could replace Mn 2+ 6. 6. Mercaptoethanol (5 mM) enhanced activity. 7. 7. EGTA [ethyleneglycol-bis (β amino ethyl ether) NN'-tetraacetic acid)] in the absence of added cations.permitted PI synthesis. 8. 8. Calcium, at 2 mM, inhibited PI synthesis. 9. 9. CDPDG :phosphohydrolase in mammary microsomes reduced PI synthesis.
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