Acyltransferases and the biosynthesis of pulmonary surfactant lipid in adenoma alveolar type II cells. |
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Authors: | F Snyder B Malone |
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Affiliation: | From the Medical and Health Sciences Division, Oak Ridge Associated Universities, Oak Ridge, Tennessee 37830 USA |
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Abstract: | Acyltransferases are present in microsomes from alveolar type II cell adenomas (produced by urethan injections) that transfer palmitic acid in the presence of CoA, ATP, and Mg++ to -glycerol-3-P to form phosphatidic acid, to dihydroxyacetone-P to form acyldihydroxyacetone-P, and to 1-acyl--glycero-3-phosphocholine to form 3--phosphatidylcholine. The data clearly demonstrate that the microsomal preparations can catalyze significant incorporation of palmitic acid into the 2-position of the disaturated species of 3-sn-phosphatidylcholine independently of phosphatidic acid formation as evidenced by the fact that -glycerol-3-P and calcium ions (which inhibit choline phosphotransferase) did not influence the incorporation of palmitic acid into the main surfactant lipid. Thus, a deacylation-acylation reaction involving 2-lysophosphatidylcholine appears to be an important pathway for the synthesis of surfactant lipid in alveolar type II cells; the control of acyl specificity at the 2-position is determined by the relative concentrations of the coparticipating substrates, l-palmitoyl--glycero-3-phosphocholine and palmitoyl-CoA. |
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