The analysis of individual gene product should enable to clarify the role of a particular enzyme in a
complex xylanase system of A. niger. The two genes encoding precursors of co-produced endo-1,4--Dxylanases,
xynA1 and xynB, were isolated from Aspergillus niger SCTCC 400264 (SCTCC, China) by
using RT-PCR technique and then successfully expressed in Escherichia coli BL21. The nucleotide
sequences of the xynA1 and xynB genes revealed that they were only 52.5% homology to each other.
Characterization of the recombinant enzymes revealed the different properties: the specific activity of
recombinant XYNA1 was 16.58 U/mg compared to 1201.7 U/mg for recombinant XYNB; The optimum
temperature and pH of the recombinant XYNA1 were 35 ºC and 3.0, respectively, whereas the
corresponding values for the recombinant XYNB were 55 ºC and 5.0, respectively; The recombinant
XYNB showed much more thermostability than recombinant XYNA1; The recombinant XYNB showed
94% of maximal activity after incubating in water for 60 min at 60 ºC compared to no activity for
recombinant XYNA1. Various metal ions had different effects on activity between the two recombinant
xylanases.
