title: Enzymatic characteristics of crude feruloyl and acetyl esterases of rumen fungus Neocallimastix sp. YAK11 isolated from yak (Bos grunniens).
abstract: Rumen fungus Neocallimastix sp. YAK11 was isolated from yak (Bos grunniens), and three consecutive 10-day pure cultures were anaerobically performed at 39 °C in 20-ml Hungate's tubes to explore ferulic acid esterase (FAE) and acetyl esterase (AE) activity profiles of the fungus grown on whole hay fraction of Chinese wildrye grass (Leymus chinensis) (WHOcw , n = 4) and its neutral detergent fibre fraction (NDFcw , n = 4), respectively. An aliquot of 0.7-ml culture was sampled daily using a sterile syringe, and 0.7-ml fresh medium was immediately added to the tubes to compensate for the withdrawn samples. Peak esterase activity occurred for FAE on day 5 (p < 0.001) and for AE on day 6 (p < 0.001). The mean activities of FAE and AE in WHOcw were 2.07 and 1.29 times of those in NDFcw (p < 0.001). Both FAE and AE activities were positively correlated with xylanase (r > 0.65, p < 0.001) and carboxymethyl cellulase (r > 0.57, p < 0.001) activities. Total volatile fatty acid concentration was positively correlated with enzyme activities of AE (r > 0.87, p < 0.001), FAE (r > 0.82, p < 0.001) and xylanase (r > 0.56, p < 0.001). Crude enzyme solution was harvested for the fungus grown on WHOcw , and the pH optimum of FAE activity was 8.0 while the optimum for AE was 9.0. Both FAE and AE had a broad pH stability range. The optimal temperatures for FAE and AE activity were 40 and 50 °C. The Michaelis constant (Km ) and maximum velocity (Vmax ) for FAE against methyl ferulate at pH 6.0 and 39 °C were 0.078 mm and 2.93 mU, respectively. The Km and Vmax for AE against p-nitrophenyl acetate at pH 7.0 and 39 °C were 2.73 mm and 666.67 mU, respectively. Both FAE and AE may have prospective advantages for the enzymatic degradation of roughages in ruminant animals.
authors.affiliation: State Key Laboratory of Animal Nutrition, College of Animal Science and Technology, China Agricultural University (CAU), Beijing, China.
authors.forename: Y C
authors.initials: YC
authors.lastname: Cao
authors.forename: H J
authors.initials: HJ
authors.lastname: Yang
authors.forename: D F
authors.initials: DF
authors.lastname: Zhang
mesh_terms: D000115:Acetylesterase / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002265:Carboxylic Ester Hydrolases / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D002417:Cattle / Q000382:microbiology*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D015966:Gene Expression Regulation, Fungal / Q000502:physiology; D020088:Neocallimastix / Q000201:enzymology* / Q000302:isolation & purification; D012417:Rumen / Q000382:microbiology*
chemical_list: D002265:Carboxylic Ester Hydrolases; D000115:Acetylesterase; C070196:feruloyl esterase