Stabilization of xylanase by random mutagenesis.

Four heat-resistant mutants of xylanase (N56, N102, N104 and F1) were obtained by random mutagenesis. The mutant genes had the following amino acid changes: N56, Ser-26 to Trp, Gly-38 to Asp and Thr-126 to Ser; N102, Gly-38 to Asp; N104, Gly-38 to Ser and Arg-48 to Lys; F1, Ser-12 to Cys. Kinetic studies showed that N104 is stabilized by an increase in the activation enthalpy, while the other mutants are stabilized by a decrease in the activation entropy.