PURIFICATION AND CHARACTERIZATION OF A NOVEL ESTERASE INDUCED BY GROWTH OF ASPERGILLUS-NIGER ON SUGAR-BEET PULP

An inducible esterase has been isolated from a liquid culture of Asper gillus niger grown on sugar-beet pulp, The enzyme was active on methyl esters of cinnamic acids, caffeic>p-coumaric>ferulic, and is therefor e termed a cinnamoyl esterase, The enzyme was not active on methyl sin apinate, a good substrate for ferulic acid esterase III, which was pur ified previously from A. niger [Faulds and Williamson (1994) Microbiol ogy 140, 779-787]. With methyl caffeate as substrate the enzyme had te mperature and pH optima of 50 degrees C and 6.0 respectively, and a sp ecific activity of 96.9 units per mg of protein, The purified protein (native molecular mass 145000 Dal gave a single heavily stained band o n SDS/PAGE, suggesting the protein was a dimer, and seemed to be heavi ly glycosylated, Isoelectric focusing gave a single band corresponding to a pi of 4.80, The pure enzyme was free of other carbohydrase activ ities, The activity of the pure enzyme was inhibited by more than 99% after treatment with the serine-specific protease inhibitor aminoethyl benrenesulphonylfluoride (1 mM) for 12 h, The enzyme was capable of re leasing ferulic acid from sugar beet pulp.