PAFの生合成並びに遊離に及ぼす食餌性脂質の効果

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1. Vitamin E deficiency was found to stimulate FMLP-induced biosynthesis of PAF in polymorphonuclear leucocytes (PMN) from rat peritoneum. The activity of the acetyltransferase, which transfers the acetyl moiety of [3H] acetyl-CoA to lysoPAF to from [3H]PAF, higher in PMN homogenates from vitamin E-deficient rats (2.28 0.07 nmol/min/mg protein) than those from E-supplemented rats(1.06 0.10 nmol/min/mg protein). However, there was no difference between the two groups in the activity of the acetylhydrolase(4.26 0.71 and 4.26 0.06 nmol/min/mg protein, respectively), measured as degradation of [3H]PAF to [3H]lysoPAF. In vitro addition of -tocopherol did not inhibit the increased activity of acetyltransferase in vitamin E-deficient rats, indicating that the enzyme in vitamin E-supplemented rats was not directly inhibited by -tocopherol. The acethyltransferases of the two groups showed similar Km values for acetyl-CoA, but different Vmax values(225 M and 6.4 nmol/min/mg protein in vitamin E- … More deficient rats, and 216 m and 3.6 nmol/min/mg protein in vitamin E-supplemented rats), suggesting that the enzyme was not activated but increased in amount in vitamin E deficiency.2. The rate of translocation of PAF across rabbit platelet plasma membranes was significantly higher than that of lysoPAF. After pretreatment of rabbit platelets with the PAF antagonist FR-900452, the translocation rate of PAF was lowered to the basal rate, which was almost equal to that of lysoPAF across plasma membranes of control rabbit platelets. Converselv, the translocation of lysoPAF was augmented by pre-activation of the platelets by PAF. These results suggested that the translocation of PAF across the bulk phase of the lipid bilayer of plasma membranes can be accelerated indirectly by activation of PAF receptors by s small protion of added lysoPAF. In both resting and activated platelets, the translocations of PAF lysoPAF through the plasma membrance were shown to be rate-liniting for the metabolic conversions of these compounds to alkylacyl-GPC. Less