Enzyme purification procedures
Banana pulps from seven different stages of ripening were cut into small pieces which were then frozen by liquid nitrogen.
The frozen pieces were blended into powder and 20 mM sodium acetate buffer, pH 5.5 was added at the ratio of 1:1 (v/v).
The final volume was 450 ml.
The suspension of each sample was centrifuged at 12,096´g for 30 min and the supernatant was used for determination of enzyme activity and protein content.
The supernatant showing the highest specific activity of xylanase was used as a crude enzyme solution.
The enzyme was then fractionated by precipitating
with ammonium sulfate at 80% saturation.
After centrifugation, the pellet was suspended in a small
volume of 20 mM acetate buffer, pH 5.5, and dialyzed against the same buffer.
The dialyzed solution was loaded onto a column (1.5 cm ´ 15 cm)
of CM-cellulose (Sigma, U.S.A.) previously equilibrated with the same buffer.
The unbound proteins were eluted with the same buffer and the
bound proteins were then eluted with a linear gradient of NaCl (0 to 500 mM) in the same buffer.
Both unbound and bound fractions were determined for xylanase and cellulase activities including protein content.
Fractions containing xylanase were pooled and concentrated by Aquasorb and dialyzed against the same buffer.
The dialyzed solution was loaded onto a column (1.5 cm ´ 90 cm) of Sephadex G-50 (Pharmacia, U.S.A.), and eluted with the same
buffer, the fractions containing xylanase activity
were pooled and concentrated by Aquasorb.
The resulting solution was used as a source of purified
xylanase.