Abstract
An endo‐xylanase. 1,4‐β‐D‐xylan xylanohydrolase (EC 3.2.1.8) from immature cucumber L. cv. Heinz 3534) seeds was partially purified using ammonium sulfate fractionation and chromatography on SP‐Sephadex and Sephadex G‐100 in order to determine its role in xylan metabolism during development. Attempts to further purify the enzyme using chromatography on DEAE‐Sephadex, Bio‐Gel HTP hydroxylapatite, Sephadex G‐200 and con A‐Sepharose 4B and native polyacrylamide gel electrophoresis resulted in a significant decrease or complete loss of enzyme activity. Endo‐xylanase had a native molecular weight of 96 kDa as determined by gel filtration, exhibited optimal activity at pH 5.0 and 48°C, and was most stable from pH 4.0 to 5.0. Using beechwood 4‐o‐methyl‐d‐glucurono‐d‐xylan dyed with Remazol Brilliant Blue R as substrate, the Km was estimated to be 0.70 mg ml−1. HgCl2 at 1 mM inhibited endo‐xylanase completely. Other metal ions inhibited the enzyme in the order Cu2+ > Fe3+ > Zn2+ > Ca2+ > Mn2+. The ethanol‐soluble products of endo‐xylanase action on beechwood xylan were isolated and characterized by consecutive chromatography on Bio‐Gel P‐10 and P‐2. The major reaction products were xylo‐oligosaccharides [degree of polymerization (dp) > 10] but traces of xylobiose and free xylose were also isolated. The formation of xylo‐oligosaccharides indicated that the reaction was catalyzed primarily by an endoxylanase. The partially pure enzyme had no activity towards other cell wall polysaccharides such as cellulose, carboxymethyl cellulose, sodium carboxyl cellulose, potato starch, orange pectin, polygalacturonic acid, arabinogalactan and β‐giucan. However, it was able to hydrolyze larchwood and oat spelts xylan and a polysaccharide component from purified cucumber cell walls. The ability to utilize a substrate from cucumber cell walls supports the hypothesis that endo‐xylanase is involved in the development of cucumber seeds.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
