Investigations of the esterase, phosphatase, and sulfatase activities of the cytosolic mammalian carbonic anhydrase isoforms I, II, and XIII with 4-nitrophenyl esters as substrates

The esterase, phosphatase, and sulfatase activities of carbonic anhydrase (CA, EC 4.2.1.1) isozymes, CA I, II, and XIII with 4-nitrophenyl esters as substrates was investigated. These enzymes show esterase activity with 4-nitrophenyl acetate as substrate, with second order rate constants in the range of 753-7706 M(-1) s(-1), being less effective as phosphatases (k(cat)/K(M) in the range of 14.89-1374.40 M(-1) s(-1)) and totally ineffective sulfatases. The esterase/phosphatase activities were inhibited by sulfonamide CA inhibitors, proving that the zinc-hydroxide mechanism responsible for the CO(2) hydrase activities of CAs is also responsible for their esterase/phosphatase activity. CA XIII was the most effective esterase and phosphatase. CA XIII might catalyze other physiological reactions than CO(2) hydration, based on its relevant phosphatase activity. (C) 2008 Elsevier Ltd. All rights reserved.