Hexose‐6‐phosphate dehydrogenase determines the reaction direction of 11β‐hydroxysteroid dehydrogenase type 1 as an oxoreductase

The impact of hexose‐6‐phosphate dehydrogenase (H6PDH) on 11β‐hydroxysteroid dehydrogenase (11β‐HSD) type 1 activity was investigated upon coexpression in HEK‐293 cells. Confocal microscopy analysis indicated colocalisation of both enzymes at the lumenal side of the endoplasmic reticulum (ER) membrane. Functional analysis in intact cells revealed fivefold stimulation of 11β‐HSD1 oxoreductase activity and sixfold decrease of dehydrogenase activity upon coexpression with H6PDH, without changing kinetic parameters in cell lysates. Thus, H6PDH directly determines the reaction direction of 11β‐HSD1 in intact cells as an oxoreductase without changing intrinsic catalytic properties of 11β‐HSD1 by regenerating NADPH in the ER‐lumen.