PORCINE 80-KDA PROTEIN REVEALS INTRINSIC 17-BETA-HYDROXYSTEROID DEHYDROGENASE, FATTY ACYL-COA-HYDRATASE DEHYDROGENASE, AND STEROL TRANSFER ACTIVITIES/

Four types of 17 beta-hydroxysteroid dehydrogenases have been identifi ed so far. The porcine peroxisomal 17 beta-hydroxysteroid dehydrogenas e type IV catalyzes the oxidation of estradiol with high preference ov er the reduction of estrone, A 2.9-kilobase mRNA codes for an 80-kDa ( 737 amino acids) protein featuring domains which are not present in th e other 17 beta-hydroxysteroid dehydrogenases. The 80-kDa protein is N terminally cleaved to a 32-kDa fragment with 17 beta-hydroxysteroid d ehydrogenase activity, Here we show for the first time that both the 8 0-kDa and the N-terminal 32 kDa (amino acids 1-323) peptides are able to perform the dehydrogenase reaction not only with steroids at the C1 7 position but also with 3-hydroxyacyl-CoA. The central part of the 80 -kDa protein (amino acids 324-596) catalyzes the 2-enoyl-acyl-CoA hydr atase reaction with high efficiency, The C-terminal part of the 80-kDa protein (amino acids 597-737) is similar to sterol carrier protein 2 and facilitates the transfer of 7-dehydrocholesterol and phosphatidylc holine between membranes in vitro. The unique multidomain structure of the 80-kDa protein allows for the catalysis of several reactions so f ar thought to be performed by complexes of different enzymes.