Type I 11-beta-hydroxysteroid dehydrogenase 1 (11beta-HSD1, HSD11B1 or HSD1) is a microsomal glycoprotein enzyme, with an apparent mass of 36 kDa. HSD-1 catalyzes the conversion of the stress hormone cortisol to the inactive metabolite cortisone. 11beta-HSD1 can also catalyze the reverse reaction, the conversion of cortisone to cortisol. 11beta-HSD1 has been detected in a wide range of rat and human tissues, including lung and testis, but highest amounts are expressed in the liver.
Human 11beta-HSD1 shares 79 and 77% sequence identity with mouse and rat 11beta-HSD1, respectively. There are at least 2 isoforms of 11beta-HSD. The other isoform, type II, is expressed predominantly in the kidney and placenta and catalyzes only the 11-beta-dehydrogenation reaction. High levels of cortisol can lead to visceral obesity and particular defects in the expression or function of 11beta-HSD1 have also been associated with insulin resistance and cognitive function.