Complementary DNAs encoding the precursor of human placental short chain acyl-coenzyme A (CoA) dehydrogenase (SCAD) (EC 188.8.131.52) were cloned and sequenced. The cDNA inserts in these clones were 1,852 bases in length combined, and encoded the entire 412-amino acid precursor SCAD (mol wt 44,303). This sequence included the 24-amino acid leader peptide moiety (mol wt 2,576) and 388 amino acids corresponding to the mature protein (mol wt 41,727). The comparison of SCAD and medium chain acyl-CoA dehydrogenase sequences revealed a high degree of homology, suggesting that these enzymes evolved from a common ancestral gene and belong to a gene family. We also studied mutant human SCAD in cultured skin fibroblasts from three patients with hereditary SCAD deficiency. Labeling fibroblast cultures with [35S]-methionine followed by immunoprecipitation with anti-SCAD antibody revealed that a normal size variant SCAD protein was synthesized. In all of the three SCAD-deficient cell lines, the size of variant SCAD mRNA as determined by Northern blotting using one of the normal SCAD cDNA as a probe was also normal, and no difference was observed on Southern blots in the restriction patterns of mutant genomic DNA using EcoRI, TaqI, HincII, and BamHI. These results suggest that the defects in SCAD in these cell lines are caused by a point mutation.
E Naito, H Ozasa, Y Ikeda, K Tanaka