Modulation of lyso-platelet-activating factor:acetyl-CoA acetyltransferase from rat splenic microsomes. The role of calcium ions |
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Authors: | Julián Gómez-Cambronero María L Nieto JoséM Mato Mariano Sánchez-Crespo |
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Institution: | 1. Nefrología Experimental, Universidad Autónoma de Madrid, Av. Reyes Católicos 2, Madrid 28040 Spain;2. Metabolismo, Nutrición y Hormonas, Fundación Jiménez Díaz, Universidad Autónoma de Madrid, Av. Reyes Católicos 2, Madrid 28040 Spain |
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Abstract: | The enzyme lyso-platelet-activating factor:acetyl-CoA acetyltransferase (EC 2.3.1.67) was assayed in microsomal fractions from rat spleens. The addition of micromolar Ca2+ rapidly enhanced acetyltransferase activity and this activation was reversed by the addition of EGTA in excess of Ca2+. The effect of Ca2+ was on the apparent of the enzyme for the substrate acetyl-CoA without showing any significant effect on the of the acetylation reaction. When microsomes were isolated in the presence of 5 mM EGTA, to remove endogenous calmodulin, the same enhancing effect of Ca2+ on the acetylation reaction was observed. The addition of exogenous calmodulin to this preparation had no effect on the enzyme activity. Preincubation of spleen microsomes with the calmodulin inhibitor trifluoperazine decreased acetyltransferase in both the presence and the absence of Ca2+, indicating an effect of this drug independently of calmodulin. The addition of Mg-ATP to the assay mixture also had no effect on the acetylation reaction. These data suggest that Ca2+ modulates acetyltransferase activity from rat spleen microsomes by a mechanism that seems to be independent of calmodulin or protein phosphorylation. |
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Keywords: | Platelet-activating factor Acetyl-CoA acetyltransferase (Rat spleen microsome) PAF-acether platelet-activating factor |
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