Light-induced stimulation of carbonic anhydrase activity in pea thylakoids

Stimulation of the bicarbonate dehydration reaction in thylakoid suspension under conditions of saturating light at pH 7.6-8.0 was discovered. This ef fect was inhibited by nigericin or the lipophilic carbonic anhydrase (CA) i nhibitor ethoxyzolamide (EZ), but not by the hydrophilic CA inhibitor, acet azolamide, It was shown that the action of EZ is not caused by an uncouplin g effect. It was concluded that thylakoid CA is the enzyme utilizing the li ght-generated proton gradient across the thylakoid membrane thus facilitati ng the production of CO2 from HCO3- and that this enzyme is covered from th e stroma side of thylakoids by a lipid barrier. (C) 2000 Federation of Euro pean Biochemical Societies.