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Long-chain acyl-CoA synthetases (ACSL) activate fatty acids (FA) and provide substrates for virtually every metabolic pathway that catabolizes FA or synthesizes complex lipids. We have hypothesized that each of the five cloned ACSL isoforms partitions FA towards specific downstream pathways. Adult heart expresses all five cloned ACSL isoforms, but their independent functional roles have not been elucidated. Studies implicate ACSL1 in both oxidative and lipid synthetic pathways. To clarify the functional role of ACSL1 and the other ACSL isoforms (3–6), we examined ACS specific activity and Acsl mRNA expression in the developing mouse heart which increases FA oxidative pathways for energy production after birth. Compared to the embryonic heart, ACS specific activity was 14-fold higher on post-natal day 1 (P1). On P1, as compared to the fetus, only Acsl1 mRNA increased, whereas transcripts for the other Acsl isoforms remained the same, suggesting that ACSL1 is the major isoform responsible for activating long-chain FA for myocardial oxidation after birth. In contrast, the mRNA abundance of Acsl3 was highest on E16, and decreased dramatically by P7, suggesting that ACSL3 may play a critical role during the development of the fetal heart. Our data support the hypothesis that each ACSL has a specific role in the channeling of FA towards distinct metabolic fates.

Lipid molecules are fundamental to cellular function and structure. Lipid metabolic events leading to these basic building blocks has been intensely studied, but are still not fully understood. Through five different studies on enzymes involved in activation and acylation of acyl groups done in three different model organisms we have uncovered novel data on lipid biosynthesis and utilization. Saccharomyces cerevisiae contains two homologous glycerol-3-phosphate acyltransferases, GPT2 and SCT1, which catalyses the first step in the acyl-lipid assembly. Deletion or over expression of the corresponding genes has not only strong effects on the glycerol-3-phsophate activity but also on the total acyl content as well as on lipid and acyl composition. (Paper I) The main form of storage lipids in seeds is Triacylglycerol. The TAZ1 from Saccharomyces cerevisiae, At104.1, and At104.2 from Arabidopsis thaliana are acyltransferase homologous genes that when overexpressed increase oil quantity in Yeast and Plants. (Patent I) Wax esters and ethyl esters are unique constituents that have roles in energy storage and cell structure. In this work we show that microsomal preparations from Arabidopsis thaliana leaves efficiently acylate free fatty acids to long chain alcohols with no activation of the fatty acids to thioesters prior to acylation. We also show that in this enzymatic reaction long chain (C18–C24) unsaturated fatty alcohols and C18–C22 unsaturated fatty acids were preferred. (Paper II) Long-chain acyl-CoA synthetases activate fatty acids and provide substrates for virtually every metabolic pathway that catabolizes FA or synthesizes complex lipids. In Mus musculus heart tissue we show that ACSL1 mRNA levels increase by 2.5 fold after birth, which correlates with the 14 fold increase in total ACSL activity at this time. In contrast,the levels of ACSL3, 4, and 6 mRNA were high in the embryonic heart, and decreased dramatically after birth suggesting that these isoforms may play a critical role during the development of the fetal heart. (Paper III) Microsomes of Saccharomyces cerevisiae and developing Elm (Ulmus glabra) seeds contain a novel type of acyltransferase activity, a acyl-CoA dependent acylation of glycerophosphodiesters. Glycerophosphocholine was acylated by yeast microsomes with a Vmax of 8.7 nmol/min/mg protein and a Km of 2.5 mM. The GPCAT activity was sensitive to NEM, phenantroline and Zn2+ ions. (Paper IV)