A ruthenium(II) complex-based carbonic anhydrase (CA) inhibitor, (Ru(bpy)2(bpybs)](2+) {bpy = 2,2'-bipyridine and bpybs = 4'-methy1-2,2,2'-bipyridiny1-4-carboxylic acid (2-{2-[(4-sulphamoylbenzoylamino)ethoxy]ethoxy}ethyl)amide}, tethering a benzenesulfonamide group and a [Ru(bpy)(3)](2+) moiety has been prepared. The CA activity was effectively suppressed by a synthetic [Ru(bpy)(2)(bpybs)](2+) inhibitor, and the dissociation constant at pH 7.2 and at 25 degrees C was determined to be K-1 = 1.9 +/- 0.2 mu M. Next, in the presence of CA and a sacrificial electron acceptor, such as pentaamminechlorocobalt(III) complex, the photoexcited triplet state of (3)([Ru(bpy)(2)(bpybs)](2+))(*) was quenched through an intermolecular photoinduced ET mechanism to form the oxidized [Ru(bpy)(2)(bpybs)](3+), followed by the intramolecular electron abstraction from an amino-acid residue near the active site of CA. The resulting oxidized CA was catalytically inactive. Kinetic experiments also revealed that the second-order rate constant for the initial step and the first-order rate constant for the second step under our experimental conditions were k(q) = 4.8 X 10(7) M-1 s(-1) and k(iET) = 6.6 X 10(4) s(-1), respectively. Thus, the intramolecular ET between CA and [Ru(bpy)(2)(bpybs)](3+) is a crucial event to regulate CA activity by the visible light irradiation of a synthetic [Ru(bpy)(3)](2+)-type inhibitor.