Subcellular distribution of carbonic anhydrase in the enterocyte of the rabbit ileum and the Caco-2 cell. Evidence for the presence of two isozymes bound to brush-border membranes.

The activity of CA has been determined in the membranes of enterocytes from rabbit ileum and of Caco-2 cells. No CA activity was detected in the BLM, but the activity in the BBM (43 and 7 WAU/mg protein for rabbit and Caco-2, respectively) was doubled by the addition of Triton. These two types of activity could be distinguished in rabbit ileum by their different IC50 in the presence of acetazolamide (10(-5) and 5 x 10(-7) M) and their different sensitivities to heat. They were not modified by inhibitors of cytoplasmic isozymes and seem to correspond to two forms of CA, one situated in the extracellular leaflet of the BBM and the other one in the intracellular leaflet.