examined three strains of Actinomadura by cultivating them on xylan and
wheat bran. The optimal pH and temperature ranges were from 6.0 to 7.0 and
between 70 and 80 °C. The half lives at 75 °C were between 6.5 and 17 h. The
record for thermostable xylanases appears to be taken by enzyme from the
primitive eubacterium Thermotoga. This organism grows optimally at 80 °C.
The half life of the enzyme at its optimum pH (5.5) is 90 min at 95 °C.
Thermostability can, however, be further improved by immobilization on glass
beads and by suspension in 90% sorbitol. Under these conditions, the half life
of the enzyme was 60 min at 130 °C (Simpson et al. 1991). Analysis of the
molecular basis for thermostable xylanases began with in vitro mutagenesis of
the xylanase from Caldocellum saccharolyticum (Luthi et al. 1992). The
enzyme shows strong sequence homology with other mesophilic xylanases, but
the presence of several charged amino acids that could form salt bridges could
account for thermostability.