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Medium-chain acyl-CoA dehydrogenase (MCAD; acyl-CoA: (acceptor) 2,3-oxidoreductase, EC 1.3.99.3) is one of three similar enzymes that catalyze the initial step of fatty acid beta-oxidation. Definition of the primary structure of MCAD and the tissue distribution of its mRNA is of biochemical and clinical importance because of the recent recognition of inherited MCAD deficiency in humans. The MCAD mRNA nucleotide sequence was determined from two overlapping cDNA clones isolated from human liver and placental cDNA libraries, respectively. The MCAD mRNA includes a 1263-base-pair coding region and a 738-base-pair 3'-nontranslated region. A partial amino acid sequence (137 residues) determined on peptides derived from MCAD purified from porcine liver confirmed the identity of the cDNA clone. Comparison of the amino acid sequence predicted from the human MCAD cDNA with the partial protein sequence of the porcine MCAD revealed a high degree (88%) of interspecies sequence identity. RNA blot analysis shows that MCAD mRNA is expressed in a variety of rat (2.2 kilobases) and human (2.4 kilobases) tissues. Blot hybridization of RNA prepared from cultured skin fibroblasts from a patient with MCAD deficiency disclosed that mRNA was present and of similar size to MCAD mRNA derived from control fibroblasts. The isolation and characterization of MCAD cDNA is an important step in the definition of the defect underlying MCAD deficiency and in understanding its metabolic consequences.
Kelly et al. (Mon,) studied this question.