The acylation of 1-palmitoyl-sn-glycerophosphocholine (1-16:0-GPC) or 1-palmitoyl-sn-glycerophosphoethanolamine (1-16:0-GPE) was measured using the microsomal fraction prepared from retinas of 14-15-day-old chick embryos. Rates of incorporation of exogenously supplied fatty acids into diacyl-GPC were generally 5-7 times greater than into diacyl-GPE. Substrate preferences for incorporation into diacyl-GPC and diacyl-GPE were, respectively, 18:2 greater than 18:3 = 20:5 greater than 20:4 greater than 18:1 greater than 22:6 = 18:0 and 18:2 greater than 22:6 greater than or equal to 18:3 = 18:0 greater than or equal to 20:4 = 18:1 greater than 20:5. The apparent selectivities were not consistent with the reported fatty acid compositions of these lipid classes. The addition of partially purified fatty acid binding protein (FABP) to the reaction had no effect either on overall rates of incorporation or on the substrate preference. When fatty acyl-CoA substrates were used, rates of incorporation of the 18:0 derivative were much higher than with the fatty acid, while rates with other fatty acyl-CoA were similar to those with the respective fatty acid. Substrate preferences for CoA derivatives incorporated into diacyl-GPC were: 18:0 greater than 20:4 greater than 18:2 greater than or equal to 22:6, and into diacyl-GPE: 20:4 = 22:6 greater than 18:0 greater than 18:2. Polyunsaturated fatty acyl CoA (PUFA-CoA) were thus favored for incorporation into diacyl-GPE, and to a lesser extent into diacyl-GPC, a result that is consistent with composition data.(ABSTRACT TRUNCATED AT 250 WORDS)
Rates of incorporation of exogenously supplied fatty acids into 1-palmitoyl-sn-glycerophosphocholine were measured using the microsomal fraction from brains of 14-15 day old chick embryos. The substrate preferences for reacylation were: 18: 2(n-6) = 20: 4(n-6) > or = 20: 5(n-3) = 18: 3(n-3) > or = 18: 1(n-9) > or = 22: 6(n-3) > or = 18: 0. The normalized rate with 18: 0 was significantly lower than all other rates except for 22: 6(n-3), and the acylation rate with 22: 6(n-3) was significantly lower than with 18: 2(n-6) and 20: 5(n-3). With the addition of fatty acid binding protein partially purified from brain cytosol, a decrease (not significant) in the rate of incorporation was observed; the substrate preference was unchanged. In the presence of FABP, normalized rates with 18: 2(n-6) were significantly higher than with 18: 0, 18: 1(n-9), or 22: 6(n-3); rates with 20: 4(n-6) were significantly higher than those with 22: 6(n-3). Preliminary data on the acylation of 1-palmitoyl-sn-glycerophosphoethanolamine showed lower rates of incorporation than for the choline analogue and no clear substrate preference, but a similar lack of effect of fatty acid binding protein. These results do not support the proposed function of fatty acid binding protein in the establishment of a phospholipid composition rich in polyunsaturated fatty acids. The results are consistent, however, with the role of the reacylation reaction in the continual turnover of particular substrates [18: 2(n-6) and 20: 4(n-6)] used to generate second messengers.
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