An high-affinity, nad-dependent 11-beta-hydroxysteroid dehydrogenase that acts unidirectionally to catalyze the dehydrogenation of CORTISOL to cortisone. It is found predominantly in mineralocorticoid target tissues such as the kidney; colon; sweat glands; and the placenta. Absence of the enzyme leads to a fatal form of childhood hypertension termed, APPARENT MINERALOCORTICOID EXCESS syndrome.