Acyl-CoA dehydrogenases [1,2,3] are enzymes that catalyze the α,β-dehydrogenation of acyl-CoA esters and transfer electrons to ETF, the electron transfer protein. Acyl-CoA dehydrogenases are FAD flavoproteins. This family currently includes:

• Five eukaryotic isozymes that catalyze the first step of the β-oxidation cycles for fatty acids with various chain lengths. These are short (SCAD) (EC 1.3.99.2), medium (MCAD) (EC 1.3.99.3), long (LCAD) (EC 1.3.99.13), very-long (VLCAD) and short/branched (SBCAD) chain acyl-CoA dehydrogenases. These enzymes are located in the mitochondrion. They are all homotetrameric proteins of about 400 amino acid residues except VLCAD which is a dimer and which contains, in its mature form, about 600 residues.
• Glutaryl-CoA dehydrogenase (EC 1.3.99.7) (GCDH), which is involved in the catabolism of lysine, hydroxylysine and tryptophan.
• Isovaleryl-CoA dehydrogenase (EC 1.3.99.10) (IVD), involved in the catabolism of leucine.
• Acyl-coA dehydrogenases acdA and mmgC from Bacillus subtilis.
• Butyryl-CoA dehydrogenase (EC 1.3.99.2) from Clostridium acetobutylicum.
• Escherichia coli protein caiA [4].
• Escherichia coli protein aidB.

We have selected two conserved regions as signature patterns. The first is located in the center of these enzymes, the second in the C-terminal section.