An intracellular carboxylesterase (EC 3.1.1.1) was isolated from Arthrobacter viscosus NRRL B-1973 and purified to homogeneity. Purification of extracted enzyme was achieved by ammonium sulfate precipitation followed by separation with Phenyl-Sepharose, DEAE-Sepharose, and Sepharose CL-6B. This carboxylesterase exhibits a specific activity of 55.4 mu mol min(-1) mg(-1) based an the hydrolysis of p-nitrophenyl acetate at pH 7.4 and 30 degrees C. The apparent molecular mass was 16.7 +/- 0.4 kDa as determined by SDS-PAGE. The isoelectric point was estimated to be 5.6 and optimum activity for the Enzyme was found at pH 7.4 and 40 degrees C. The enzyme removed acetyl residues from xanthan, alginate, glucose pentaacetate, cellobiose octaacetate, and the native exopolysaccharide produced by A. viscosus and also deacetylated p-nitrophenyl propionate, naphthyl acetate, isopropenyl acetate, and triacetin. This enzyme demonstrates a restricted chain-length specificity for deacetylation of a wide variety of low and high molecular weight esters. Preliminary investigations indicate that it can also catalyze transesterifications from selected acyl donors to polymeric accepters, notably cellulose.