Isolation and partial characterization of alkaline feruloyl esterases from Aspergillus niger CFR 1105 grown on wheat bran

Feruloyl esterases (FAEs) of a strain of
Aspergillus niger (CFR 1105) grown in solid state (ssf) and
submerged fermentations (smf) using wheat bran both as
carbon source and inducer of the enzyme were studied. The
feruloyl esterase activity was maximum after 4 days in
solid state as well as in submerged fermentations (32.5 and
31.5 U/g dry weight of wheat bran respectively) and the
enzyme titers were comparable. The specific activity was
maximum on day 2 in ssf (12.8 U/mg protein) and it
decreased thereafter, whereas specific activity was maximum
on day 3 (11.7 U/mg protein) in smf and it remained
constant up to 5 days. Two isoenzymes of feruloyl esterases
were isolated and purified to homogeneity by conventional
protein purification methods from the day 5
culture filtrate of A. niger grown in smf. On a DEAEcellulose
column, two enzyme activity peaks designated as
FAE-1 and FAE-2 were eluted with 0.3 and 0.35 M NaCl,
respectively. They were monomeric glycoproteins with
approximate molecular weights of 50 kDa (FAE-1) and
55 kDa (FAE-2), respectively. FAE-1 showed a temperature
optimum of 40�C whereas FAE-2 showed a wider
temperature optimum of 40–50�C. FAE-1 and FAE-2
exhibited pH optima of 9 and 6, respectively, and both
were stable over a pH range of 6–9. The ability of the
enzyme to be active in alkaline pH may be advantageous in
biotechnological applications.