Purification and characterization of a major esterase BesB from hemolymph of the silkworm Bombyx mori

Abstract

Total esterase activity in the hemolymph of Bombyx mori was measured using a-naphthyl acetate as a substrate. It was low during the early fifth instar, then sharply increased at the spinning stage and stayed high throughout the pupal stage. One of the major hemolymph esterases of B. mori, previously named BesB (blood esterase B type), was purified from day 1 pupae to homogeneity using procedures such as procainamide hydrochloride affinity chromatography. BesB had an apparent molecular weight of 58,000 and an isoelectric point of 4.6. It was most active at pH 6-7, and was stable around pH 7 to 9. The sequence of N-terminal 28 amino acid residues was partially homologous to previously reported esterases isolated from the peach-potato aphid Myzus persicae. In kinetic parameters, there were no differences in Km values from four tested substrates, but there were differences in Vmax values. BesB had the highest sensitivity to paraoxon and diisopropyl f luorophosphate (DFP), and was moderately affected by eserin sulfate, phenylmethylsulf onyl fluoride (PMSF) and chloromercuribenzoic acid (pCMB). These results indicate that BesB is a carboxylesterase in hemolymph.