Complementary DNAs encoding the precursor of human placental short chain
acyl-coenzyme A (
CoA)
dehydrogenase (SCAD) (EC 1.3.99.2) 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.