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The biosynthesis of polyunsaturated fatty acids (PUFAs) in bacteria has been extensively studied. In contrast, studies of PUFA metabolism remain limited. Shewanella livingstonensis Ac10 is a psychrotrophic bacterium producing eicosapentaenoic acid (EPA), a long-chain ω-3 PUFA. This bacterium has the ability to convert exogenous docosahexaenoic acid (DHA) into EPA and incorporate both DHA and EPA into membrane phospholipids. Our previous studies revealed the importance of 2,4-dienoyl-CoA reductase in the conversion, suggesting that DHA is metabolized through a general β-oxidation pathway. Herein, to gain further insight into the conversion mechanism, we analyzed the role of acyl-CoA dehydrogenase (FadE), the first committed enzyme of the β-oxidation pathway, in DHA conversion. S. livingstonensis Ac10 has two putative FadE proteins (FadE1 and FadE2) that are highly homologous to Escherichia coli FadE. We found that FadE1 expression was induced by addition of DHA to the medium and fadE1 deletion reduced DHA conversion into EPA. Consistently, purified FadE1 exhibited dehydrogenase activity towards DHA-CoA. Moreover, its activity towards DHA- and EPA-CoAs was higher than that towards palmitoleoyl- and palmitoyl-CoAs. In contrast, fadE2 deletion did not impair DHA conversion, and purified FadE2 had higher activity towards palmitoleoyl- and palmitoyl-CoAs than towards DHA- and EPA-CoAs. These results suggest that FadE1 is the first enzyme of the β-oxidation pathway that catalyzes DHA conversion.

Breeding experiments were conducted to combine the X-linked sparse-fur (spf) mutation with ornithine transcarbamylase deficiency and the autosomal recessive deficiency of short-chain acyl CoA dehydrogenase (SCAD) in BALB/cByJ mice. We obtained spf/Y (scad/scad), spf/+ (scad/scad) and spf/spf (scad/scad) double mutants amongst the F2 progeny, which were tested and separated on the basis of urinary orotate and the GC/MS analysis of urinary butyrylglycine, methylsuccinate and ethylmalonate. The testing of the biochemical type was feasible both on the basis of a 24-h urine collection form adult mice kept in metabolic cages and on the basis of urine spots collected on filter paper from younger progeny. It is postulated that the spf/Y (scad/scad) double-mutant may serve as a useful animal model to study the ammonia: fatty acyl CoA synergism.

Acyl-CoA dehydrogenases (ACADs) are a family of mitochondrial enzymes catalyzing the initial rate-limiting step in the β-oxidation of fatty acyl-CoA. The reaction provides main source of energy for human heart and skeletal muscle. Eight human ACADs have been described. Deficiency of these enzymes, especially very long-chain acyl-CoA dehydrogenase (VLCAD), usually leads to severe human organic diseases, such as sudden death in infancy, infantile cardiomyopathy (CM), hypoketotic hypoglycemia, or hepatic dysfunction. By large-scale random sequencing, we identified a novel homolog of ACADs from human dendritic cell (DC) cDNA library. It contains an open reading frame (ORF) of 1866 bp, which encodes a 621 amino acid protein. It shares approximately 47% amino acid identity and 65% similarity with human VLCAD. So, the novel molecule is named as acyl-CoA dehydrogenase-9 (ACAD-9), the nineth member of ACADs. The new gene consists of 18 exons and 17 introns, and is mapped to chromosome 3q26. It contains the two signatures shared by all members of the ACADs. ACAD-9 mRNA is ubiquitously expressed in most normal human tissues and cancer cell lines with high level of expression in heart, skeletal muscles, brain, kidney, and liver. Enzymatic assay proved that the recombinant ACAD-9 protein has the dehydrogenase activity on palmitoyl-coenzyme A (C16:0) and stearoyl-coenzyme A (C18:0). Our results indicate that ACAD-9 is a novel member of ACADs.

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is one of the most common recessively inherited metabolic diseases in man. We have studied fibroblast cultures obtained from three patients with MCAD deficiency by sequencing the entire coding region of MCAD mRNA. A single A to G nucleotide replacement which resulted in lysine329-to-glutamic acid329 substitution of the MCAD protein was identified in all cultures. Furthermore, this point mutation was present in 91% (31 of 34) of mutant MCAD alleles, indicating that the majority of cases with MCAD deficiency are caused by this type of mutation.

[2- 14 C]- trans -2-hexadecenoyl CoA (16:1) and [2- 14 C]- trans -2-cis-8,11,14-eicosatetraenoyl CoA (20:4) were chemically synthesized and employed as competitive substrates for the liver microsomal trans -2-enoyl CoA reductase component of the fatty acid chain elongation system. Both 7.5 μM and 15 μM 20:4 competitively inhibited the reduction of 16:1 CoA to palmitoyl CoA. In addition, the reduction of both substrates was identically inhibited to the same extent by the acetylenic derivative, dec-2-ynoyl CoA. Furthermore, trypsin, chymotrypsin and subtilisin inhibited trans -2-enoyl CoA reductase activity when three different substrates were employed—16:1, 20:4 and trans -2-cis-11-octadecadienoyl CoA (18:2). These results are consistent with the hypothesis of multiple condensing enzymes connected to a single elongation pathway.

Kinetics of inactivation of general acyl-CoA dehydrogenase from pig kidney by methylenecyclopropaneacetyl-CoA have been analyzed using the theoretical treatment and exact steady-state kinetic solutions reported by Tatsunami (Tatsunami, S., Yago, N., and Hosoe, M. (1981) Biochim. Biophys. Acta 662 , 226–235). Thus practical application of these analytical solutions for an important class of enzyme: substrate reactions has been demonstrated for the first time.

Summary The kinetics of reduction of the electron transfer flavoprotein were investigated by fluorimetric analysis of kinetic single progress curves. The steady state reaction was catalyzed by the general acyl CoA dehydrogenase and-butyryl CoA under anaerobic conditions. The results of these experiments show that the semiquinone form of the electron transfer flavoprotein is a product inhibitor of the dehydrogenase. It is suggested that such product inhibition may modulate flux through the electron transfer flavoprotein-linked flavoprotein dehydrogenases.

In vitro synthesis of general acyl CoA dehydrogenase [EC 1.3.99.3], one of the mitochondrial flavoenzymes, was carried out to elucidate its biosynthetic mechanism. Poly(A)+ RNA isolated from pig kidney was translated in vitro using wheat germ lysate system and the synthesized enzyme was immunoprecipitated by the antibody against purified pig kidney general acyl CoA dehydrogenase. The apparent molecular weight of the synthesized protein was estimated to be approximately 1,000 daltons larger than that of the mature enzyme, indicating that general acyl CoA dehydrogenase in pig kidney is synthesized as a precursor with a larger molecular weight.