Characterization of a β-Glucosidase Produced by a High-Specific Growth-Rate Mutant of Cellulomonas flavigena

Abstract

The mutant strain PN-120 of Cellulomonas flavigena produces a ß-glucosidase that is 10-fold more active than the corresponding enzyme isolated from the parental strain. These enzymes were partially purified through Q Sepharose and Bio-Gel filtration. A single protein band was detected on polyacrylamide–gel electrophoresis/zymogram using 4-methylumbelliferyl-β-D-glucoside. On sodium dodecyl sulfate–PAGE, the enzyme displayed three protein bands, suggesting that in C. flavigena the enzyme is oligomeric with a molecular mass of 210 kDa. On purification, the specific activity of ß-glucosidase isolated from PN-120 was increased 16-fold and showed three times more affinity for cellobiose than the enzyme of the parental strain; nevertheless, the optimum pH and temperature were similar for both enzymes. The kinetic parameters suggested that the increase in the activity of the enzyme, from the mutant strain, was caused by a mutation that affects the catalytic site of the enzyme. The partial amino-acid sequence of the isolated enzyme confirmed that it is a β-glucosidase because of its homology with other β-glucosidases produced by cellulolytic bacteria and fungi.