Characterization of a cellulase from the haemolymph of the giant African snail (Archachatina marginata)

Abstract

The giant African snails (Archachatina marginata) are herbivorous tropical gastropods. They are  commonly  located in areas littered with decaying vegetable matters which they feed on. When the haemolyph of this  organism was passed through Sephadex G-200, the resin was digested. The ability of snails to digest vegetable matters and the digestion of Sephadex G-200 resin by the haemolyph led to the suspicion of the presence of  cellulase in snail haemolyph. Cellulase from haemolyph of the giant African snail was purified to homogeneity by a combination of gel filtration on BioGel P-300 and ion-exchange chromatography on DEAE-Sephadex. The homogeneity of the pure enzyme was adjudged by polyacrylamide gel electrophoresis in the absence and  presence of sodium dodecyl sulphate. The subunit molecular weight was 16,875±1,556 daltons and the  apparent molecular weight as determined by gel filtration was 52,000 daltons. Thus, the enzyme is at least a dimer. The enzyme had a specific activity of 1359.09 units/mg of protein. The Michaelis-Menten constant (K_max) for carboxymethyl (CM)-cellulose was 5.17± 0.74 mg/ml and the maximum velocity (V_max) was 1067±195 units/ml. The enzyme did not degrade salicin, cellobiose and o-nitrophenyl-β-D-glucopyranoside. In addition,  its activities towards filter paper and cotton wool were insignificant compared with its activity towards  CM-Cellulose. Linamarin was found to inhibit the action of the enzyme to about 18%. The high specificity for CM-cellulose and the rapid decrease in the viscosity of CM-cellulose suggests that the enzyme is likely an endoglucanase.

Key words: Snail, cellulase, endoglucanase, heamolymph, gastropod.