PURIFICATION, CHARACTERIZATION AND PROPERTIES OF CARBOXYLESTERASE FROM THE MIDGUT OF THE SILKWORM, BOMBYX-MORI L

A carboxylesterase has been purified from the midgut of the silkworm B ombyx mori L. by a combination of ammonium sulphate fractionation, DEA E-cellulose ion-exchange chromatography, Sephacryl S-200 gel-filtratio n and preparative polyacrylamide gel electrophoresis (PAGE). The homog eneity of the enzyme was established by PAGE, isoelectricfocusing (IEF ) and SDS-PAGE. The enzyme consists of two identical subunits with a s ubunit molecular weight of 72,000. The two subunits are held by non-co valent bonds, Amino acid amalysis of the purified enzyme revealed a hi gh content of hydrophobic amino acid residues. It lacks proline and tr yptophan residues and free thiol groups. The data from substrate speci ficity study in conjunction with kinetic parameters indicate the hydro phobic nature of the active site.