An extremely thermostable cellulase from the thermophilic eubacterium Rhodothermus marinus

An extracellular endo-β-1,4-glucanase purified from Rhodothermus marinus was active on carboxymethyl cellulose but not on Avicel, Sigmacell 10 cellulose, granular cellulose, p-nitrophenyl-β-D-cellobioside, or 4- methylumbelliferyl-β-D-cellobioside. The hydrolysis products of carboxymethyl cellulose were glucose, cellobiose, and cellotriose, as well as a mixture of cellopentaose and larger oligosaccharides. The main degradation product of cellotriose, cellotetraose, and cellopentaose was cellobiose. The apparent monomeric molecular weight was about 49,000, and the pH optimum was at 7.0. The enzyme is the most thermostable endocellulase reported to date, retaining 50% of its activity after 3.5 h at 100°C and 80% after 16 h at 90°C.