Affiliation:
1. Stazione Sperimentale per La Cellulosa, Carta e Fibre Tessili Vegetali ed Artificiali, Milan 20133, Italy
2. University of Technical Sciences, Budapest Institute of Agricultural Chemical Technology, Budapest, Hungary
3. Institute for Microbial and Biochemical Technology, Forest Products Laboratory, Forest Service, U.S. Department of Agriculture, Madison, Wisconsin 53705
Abstract
The endoxylanase complex from
Streptomyces
sp. strain B-12-2 was purified and characterized. The organism forms five distinct xylanases in the absence of significant cellulase activity when grown on oat spelt xylan. This is the largest number of endoxylanases yet reported for a streptomycete. On the basis of their physiochemical characteristics, they can be divided into two groups: the first group (xyl 1a and xyl 1b) consists of low-molecular-mass (26.4 and 23.8 kDa, respectively) neutral- to high-pI (6.5 and 8.3, respectively) endoxylanases. Group 1 endoxylanases are unable to hydrolyze aryl-β-
d
-cellobioside, have low levels of activity against xylotetraose (X
4
) and limited activity against xylopentaose, produce little or no xylose, and form products having a higher degree of polymerization with complex substrates. These enzymes apparently carry out transglycosylation. The second group (xyl 2, xyl 3, and xyl 4) consists of high-molecular-mass (36.2, 36.2, and 40.5 kDa, respectively), low-pI (5.4, 5.0, and 4.8, respectively) xylanases. Group 2 endoxylanases are able to hydrolyze aryl-β-
d
-cellobioside, show higher levels of activity against X
4
, and hydrolyze xylopentaose completely with the formation of xylobiose and xylotriose plus limited amounts of X
4
and xylose. The enzymes display intergroup synergism when acting on kraft pulp. Despite intragroup similarities, each enzyme exhibited a unique action pattern and physiochemical characteristic. xyl 2 was highly glycosylated, and xyl 1b (but no other enzyme) was completely inhibited by
p
-hydroxymercuribenzoate.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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