Purification and partial characterization of rat intestinal cefuroxime axetil esterase

An esterase which hydrolyses the cephalosporin antibiotic, cefuroxime axetil has been isolated from rat intestinal washings and purified. Closely related cefuroxime esters were extremely poor substrates, but p-nitrophenyl acetate and alpha-naphthyl acetate were slowly hydrolysed by the purified enzyme. Analysis by gel filtration gave an Mr = 51,000 and on SDS-polyacrylamide gel electrophoresis the esterase resolved into two main bands of Mr = 31,500 and 26,800. Analytical isoelectric focusing resolved purified esterase into multiple forms active toward alpha-naphthyl acetate, the isoelectric points of which ranged from pH 4.5 to 6.3. The esterase bound specifically to Con A-Sepharose suggesting it could be a glycoprotein. Esterase activity was unaffected by the presence of dihydroxy bile salts (1-8 mM) and inhibition studies using organophosphates and eserine salicylate have classified the enzyme as a carboxylesterase.