Δ3,5-Δ2,4-dienoyl-CoA isomerase from rat liver -: Molecular characterization

rECH1, a recently identified rat cDNA (FitzPatrick, D. R., Germain-Lee, E., and Valle, D. (1995) Genomics 27, 457-466) encodes a polypeptide belonging to the hydratase/isomerase superfamily, We modeled the structure of rECH1 based on rat mitochondrial 2-enoyl-CoA hydratase 1, The model predicts that rECH1p has the hydratase fold in the core domain and two domains for interaction with other subunits. When we incubated 3,5,8,11,14-eicosapentaenoyl-CoA with purified rECH1p, the spectral data suggested a switching of the double bonds from the Delta(3)-Delta(5) to the Delta(2)-Delta(4) positions. This was confirmed by demonstrating that the product was a valid substrate for 2,4-dienoyl-CoA reductase, These results indicate that rECH1p is Delta(3,5)-Delta(2,4)-dienoyl-CoA isomerase, Subcellular fractionation and immunoelectron microscopy using antibodies to a synthetic polypeptide derived from the C terminus of rECH1p showed that rECH1p is located in the matrix of both mitochondria and peroxisomes in rat liver, Consistent with these observations, the 36,000-Da rECH1p has a potential N-terminal mitochondrial targeting signal as well as a C-terminal peroxisomal targeting signal type 1, Transport of the protein into the mitochondria with cleavage of the targeting signal results in a mature mitochondrial form with a molecular mass of 32,000 Da; transport to peroxisomes yields a protein of 36,000 Da.