Abstract
l-Arabinose isomerases catalyze the bioconversion of
d-galactose into
d-tagatose. With the aim of producing an enzyme optimized for
d-tagatose production, three
Bacillus stearothermophilus US100
l-arabinose isomerase mutants were constructed, purified and characterized. Our results indicate that mutant Q268K was significantly more acidotolerant and more stable at acidic pH than the wild-type enzyme. The N175H mutant has a broad optimal temperature range from 50 to 65
°C. With the aim of constructing an acidotolerant mutant working at relatively low temperatures we generated the Q268K/N175H construct. This double mutant displays an optimal pH in the range 6.0–7.0 and an optimal activity around 50–65
°C, temperatures at which the enzyme was stable without addition of metal ions.