Monday, August 2, 2010
Pacific Concourse (Hyatt Regency San Francisco)
Acremonium zeae, one of the most prevalent fungal colonists of preharvest maize, produces a full complement of hemicellulolytic enzymes including xylanase, xylosidase, and arabinofuranosidase activities. In the present study, two arabinofuranosidases were purified to electrophoretic homogeneity from cell-free culture supernatants of A. zeae grown on oat spelt xylan. The 47 kDa arabinofuranosidase (AF47) is optimally active at 37°C and pH 6.0, and has a specific activity for 4-nitrophenyl-α-L-arabinofuranoside (4NPA) of 6.3 U/mg. The 30 kDa enzyme (AF30) is optimally active at 50°C and pH 4.5, and has a specific activity for 4NPA of 16 U/mg. The two enzymes have distinct substrate specificities. AF47 acted on a broad range of substrates, capable of hydrolyzing 4-nitrophenyl-β-D-xylopyranoside, 4-nitrophenyl-β-D-glucopyranoside, and 4-nitrophenyl-β-D-cellobioside, as well as producing reducing sugar from xylans from oat spelts, birch wood, wheat, and corn fiber. In contrast, AF30 preferred the xylan substrates and did not display any detectable activity on the 4-nitrophenyl substrates (except for 4NPA). AF30 activity on xylans from corn fiber, oat spelts, and birch wood was approximately 10-fold higher than AF47, and on wheat arabinoxylan, was 40-fold higher with a specific activity of 1200 U/mg. On corn fiber xylan, AF30 and AF47 acted synergistically to produce greater than 60% more reducing sugar than the sum of the individual enzymes. The arabinofuranosidases produced by A. zeae may have industrial application for the hydrolysis of recalcitrant lignocellulosic feedstocks such as corn fiber and wheat straw.