Abstract
17 beta-Hydroxysteroid dehydrogenase (17 beta-HSD) is an enzyme crucial to the regulation of intracellular levels of biologically active steroid hormones in a variety of tissues. Here, we report the isolation, structure, and characterization of a cDNA encoding the human 17 beta-HSD type 2. A 1.4-kilobase cDNA was identified, and DNA sequence analysis indicated that 17 beta-HSD type 2 was a protein of 387 amino acids with a predicted molecular weight of 42,782. The protein contained an amino-terminal type II signal-anchor motif and a carboxyl-terminal endoplasmic reticulum retention motif, which suggested that 17 beta-HSD type 2 was associated with the membranes of the endoplasmic reticulum. 17 beta-HSD type 2 was capable of catalyzing the interconversion of testosterone and androstenedione as well as estradiol and estrone. The enzyme also demonstrated 20 alpha-HSD activity toward 20 alpha-dihydroprogesterone. The amount of 17 beta-HSD type 2 mRNA in placenta was found to be high. The data suggest that the 17 beta-HSD type 2 cDNA encodes the microsomal 17 beta-HSD of human placenta, described by several laboratories.
Highlights
178-Hydroxysteroid dehydrogenas(e178-HSD)is an unknown; a considerable body of evidence suggests that 178 enzyme crucial to the regulation of intracellulleavrels reduction and oxidation of androgens and estrogens are catof biologicallyactive steroid hormones in avariety of alyzed by different isozymes with distinct substrate specificitissues
178-HSD type 2 was capable of catalyzing the inter- human placental microsomes: one that is highly specific for conversion of testosterone and androstenedaisowneell estrogens, and a second isozyme that utilizes both androgens as estradiolandestrone.Theenzyme demon- and estrogens as substrates (7)
This paper describes the isolation and characterization of a full-length cDNA for the human 17P-HSD type 2, a membrane-bound enzyme that possesses both 17P-HSD and 20aHSD activities against androgense,strogens, and progestins
Summary
63 1993 by The American Society for Biochemistryand Molecular Biology, Inc. Vol 268, No 17, Iseue of June 15, pp. 12964-12969 1993 Printed in $ S A. Steroids were added in 2-5 p1 of ethanol, and the reaction was initiated by the addition of NAD+ (testosterone, dihydrotestosterone, estradiol, an2d0dihydroprogesterone) or is the extended hydrophobic amino terminus of the type 2 enzyme. This region corresponds to the putative transmembrane signal anchor. To characterize the biochemical properties of the human 17&HSD type 2 enzyme, the high levels of expression in transiently transfected[293] cells made it possible to assay 17PHSD activity in vitro in homogenates from transfected cells. 27.5 isolated from human placental mRNA using a reverse-transcriptase-PCR cloningstrategy Taken together, these results suggested that the 17P-HSD type[2] gene is highly expressed in placenta
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