CLONING AND EXPRESSION OF CDNA FOR A NEWLY IDENTIFIED ISOZYME OF BOVINE LIVER 3-HYDROXYACYL-COA DEHYDROGENASE AND ITS IMPORT INTO MITOCHONDRIA

cDNA for a heretofore undescribed mitochondrial 3-hydroxyacyl-CoA dehy drogenase, designated the type II enzyme with different molecular and catalytic properties, compared to those of the classical mitochondrial beta-oxidation enzyme (type I enzyme), was cloned from a bovine liver cDNA library. Nucleotide sequence of the cDNA encoded 261 amino acids with a subunit molecular weight of 27 140. The deduced primary struct ure of the type II enzyme showed no significant homology to the report ed amino acid sequence of the classical 3-hydroxyacyl-CoA dehydrogenas es. On SDS-PAGE, no differences in subunit molecular weights were obse rved among the in vitro translation products, the recombinant type II enzyme produced in Escherichia coli and the purified enzyme. NH2-termi nal and COOH-terminal amino acid Sequence analysis of the purified typ e II enzyme revealed that the mature enzyme had not been proteolytical ly processed: The in vitro translation products of the type II enzyme were efficiently incorporated into isolated rat liver mitochondria, wi thout change in size, thereby suggesting that unlike other mitochondri al enzymes of fatty acid beta-oxidation, the type II enzyme had no cle avable signal peptide upon import into mitochondria.