Heterogeneity in the metabolism of the arachidonoyl molecular species of glycerophospholipids of rabbit alveolar macrophages

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Abstract
The relative incorporation of [3H]arachidonic acid (20:4) into individual molecular species containing 20:4 at the 2 position (18:1 ‐ 20:4, 16:0 ‐ 20:4 and 18:0 ‐ 20:4 species) of diacyl and ether‐linked glycerophosphocholine, glycerophosphoethanolamine and glycerophosphoinositol of rabbit alveolar macrophages has been measured by reversed‐phase high‐performance liquid chromatography (HPLC). The rate of incorporation of [3H]20:4 into the molecular species of glycerophospholipids was greatly influenced by their structures. The reversed‐phase HPLC analysis allowed elucidation of the influence of structural differences, such as the nature of the polar head group, the fatty chain at the 1 position and the chemical form of the bond of the fatty chain attached at the 1 position on the uptake of [3H]20:4 by comparison of the specific radioactivities of arachidonoyl molecular species having the same structures, except that one of the three kinds of moiety was different. The specific radioactivities of the molecular species containing choline head groups were significantly higher than those containing ethanolamine and inositol moieties. The specific radioactivities of diacyl molecular species were considerably higher than those of ether‐linked molecular species. The nature of the fatty chain attached at the 1 position also influenced the uptake of [3H]20:4 into glycerophospholipids. The arachidonoyl molecular species containing 18:1 at the 1 position were preferentially labelled with [3H]20:4 as compared to the corresponding 16:0 ‐ 20:4 and 18:0 ‐ 20:4 species either of diacyl or ether‐linked glycerophospholipids. The present results suggest that the acyltransferase involved in the incorporation of 20:4 into glycerophospholipids has selectivity for the structures of glycerophospholipids and the order of selectivity of this enzyme for the arachidonoyl molecular species, deduced in the present experiments, was as follows: choline head group > ethanolamine and inositol groups, acyl bond > ether and vinyl ether bonds, 18:1 fatty chain > 16:0 and 18:0 fatty chains at the 1 position. Comparison of the metabolic activities of all major arachidonoyl molecular species of glycerophospholipids having a single structure is reported here for the first time.

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