Sunday, August 12, 2012
Columbia Hall, Terrace Level (Washington Hilton)
Enzymes have been used for industrial purposes in different areas like food production, biofuels, paper, etc. One of these enzymes are xylanases which are glycosyl hydrolases that hydrolyze β(1-4) glycoside bonds, degrading xylan fibers, second most abundant polymers on vegetal cell wall. Filamentous fungi are the main source of hydrolases. Lichtheimia ramosa is a thermotolerant mucoral fungi that presents lignocellulolytic activity. The aim of this study was to purify and characterize a xylanase from the thermotolerant fungi L. ramosa strain H71D, isolated from sugar cane bagasse. Fermentations were carried at 37 °C, 160 r.p.m. using a mineral medium with carboximetylcellulose (CMC) as substrate. Xylanase activity was determinated quantifying reducing sugars with DNS method. A 64 kDa xylanase was purified from the culture supernatant of L. ramosa strain H71D, after precipitation with 70% (NH4)2SO4 and one step of ion exchange chromatography. The xylanase was purified to 6.4-fold apparent homogeneity with a recovery yield of 38.5% yielding a specific activity of 126.43 U/mg of protein. The enzyme displayed optimal activity at pH 6.0 and 65 °C with kinetic parameters Km of 2.87 mg/ml and Vmáx of 6.97 mg/ml. Xylanase activity was stimulated by Ca2+, Mn2+ and Fe3+, up to 300% with Fe3+ 5mM; while Hg2+ decreased the activity almost completely. Thermostability of 25 min at 65 °C.