Abstract:
The present work reported D-glucose isomerase production by Streptomyces PC22 and CH7, efficient xylanase- and β-xylosidase-producing strains, respectively. The enzyme production required xylose as an inducer and the maximum activities of 1.2 and 1.8 U/mg were obtained from PC22 and CH7, respectively when grown on 2% xylose. With 1% xylan as a carbon source, higher glucose isomerase activities of 3.5 and 5.0 U/mg were produced from PC22 and CH7, respectively. When hemicellulosic agricultural residues were used to replace an expensive xylan, 2% wheat bran was the best carbon source for PC22 whereas 2.5% corn husk was for CH7 giving considerably good levels of the enzyme productions of about 2.2 and 3.1 U/mg, respectively. The enzymes from PC22 and CH7 were then purified by consecutive column chromatography on Macro-prep DEAE and Sephacryl-300 to approximately 20 and 16 folds with recovery yields of 38.6% and 46.6 %, respectively. The apparent molecular weights of the pure enzymes from both strains were similar of 170 kDa estimated by gel filtration and revealed four identical subunits of 43.6 kDa estimated by SDS-PAGE. The enzymes from PC22 and CH7 had temperature optima of 80oC and 85oC, respectively but they had the same pH optimum of 7.0. The enzymes were stable to temperature up to 50oC for PC22 and 60oC for CH7 and to broad ranges of pH from 6.0-8.0 for PC22 and 6.0-7.0 for CH7. The Km values of the enzymes for glucose and xylose were 435.9 and 177.3 mM for PC22 and 258.96 and 82.77 for CH7, respectively. The enzymes required both Mg2+ and Co2+ for their activities in which Co2+at 0.1mM for both enzymes and Mg2+ at 5mM for PC22 and 10 mM for CH7 gave the maximum enzyme activities. Furthermore, the present work also determined inulinase-producing abilities of PC22 and CH7 when grown on inulin extract from Jerusalem artichoke. Both PC22 and CH7 could produce inulinases of about 0.12 and 0.16 U/ml, respectively. Temperature optima of 60o C and 65o and pH optima of 6.0 and 6.5 were for inulinases from PC22 and CH7, respectively.