The gene encoding sucrose isomerase ( palI NK33) was cloned from Klebsiella pneumoniae strain NK33-98-8. The gene was over-expressed in Escherichia coli BL21 (DE3) pLysS and its enzyme product (PalI NK33) was purified and characterized. PalI NK33 converts sucrose to 76.8% palatinose, 21.2% trehalulose and 1% each of glucose and fructose. The purified PalI NK33 showed the very high specific activity at 2362 U/mg and K m for sucrose was 42.7 ± 0.75 mM (at pH 6.0 and 30 °C). The enzyme activity was completely inhibited by 1 mM concentration of either Hg 2+ or SDS. Ca 2+, Li 2+ and Mg 2+ at 1 mM slightly enhanced enzyme activity. Mutations on Asp140, located within the conserved sequence region I to either glutamic acid, glycine or asparagine had drastically reduced enzyme activity. The change of amino acid residues in the sequence 325RLDRD 329 to 325RYDRA 329 reduced enzyme activity 24-fold and did not affect ratio of palatinose and trehalulose formation.
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