General esterases of silkmoth moulting fluid: Preliminary characterization

The moulting fluid of silkmoths contains not only proteolytic enzymes with amino acid esterase activity, but also two naphthyl esterases (general esterases). These enzymes have been partially purified and separated by sucrose density-gradient centrifugation and DEAE-cellulose column chromatography. One is weakly anionic at pH 8 and has a molecular weight of 64,000; the other is cationic and has a molecular weight of 57,000. Both enzymes are most stable under the mildly alkaline pH conditions characteristic of moulting fluid but are irreversibly inactivated at acid pH. Both are inhibited by diisopropyl fluorophosphate, although at different rates. The enzymes hydrolyse low molecular weight esters of aromatic alcohols, but lack proteolytic activity; inhibition and specificity studies suggest that they are carboxyl esterases. They are found throughout development, in both moulting gel and moulting fluid; their rôle in the moulting process is as yet unclear.