Louis, USA) in 10 ml of 0.1 M sodium maleate buffer (pH 6.9) in a shaking water bath at 37 C. Aliquots of 200 ll were withdrawn during the incubation period and mixed with 200 ll of ethanol (96%, w/w) to stop the enzymatic reaction and the sample was centrifuged at 10,000g for 5 min at 4 C.