, Volume 144, Issue 5, pp 947-953
Date: 10 Dec 2003

Purification and characterization of an endo-1, 4-β-D glucanase from the cellulolytic system of the wood-boring marine mollusk Lyrodus pedicellatus (Bivalvia: Teredinidae)

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Abstract

The soluble fraction of crude tissue homogenates prepared from intact specimens of the shipworm Lyrodus pedicellatus Quatrefages was observed to increase the reducing sugar content of solutions of carboxymethylcellulose (CMC). The predominant CMCase activity detected in these lysates by zymography corresponds to a polypeptide of approximately 40 kDa. This protein, designated Lp-egl-1, was purified and characterized. Experiments described in this study were performed in 1997 using L. pedicellatus from a culture maintained at the Woods Hole Oceanographic Institution. Purified Lp-egl-1 increases reducing sugar content of solutions of CMC and suspensions of phosphoric acid–swollen cellulose, decreases viscosity of CMC solutions, and cleaves the oligosaccharides cellopentaose and cellotetraose internally to release cellotriose and cellobiose. It has no detectable activity against microcrystalline cellulose, cellotriose, cellobiose, or p-nitrophenyl β-D-glucopyranoside and does not release glucose from any tested substrate. These results are consistent with the conclusion that Lp-egl-1 is an endo-1, 4-β-D glucanase (E.C. 3.2.1.4). The K m value of Lp-egl-1 for CMC is 20 mg ml−1. The enzymatic activity is inhibited by cellobiose and cellotriose, but not by glucose. Lp-egl-1 differs in molecular mass as well as kinetic and immunological properties from a previously described endoglucanase secreted by a cultivable endosymbiont of shipworms, Teredinibacter turnerae Distel et al., 2002. It has not been determined whether Lp-egl-1 is a product of the L. pedicellatus nuclear genome or of an associated symbiotic microbe.

Communicated by J.P. Grassle, New Brunswick