337.
Bifidobacterium longum NRRL B-41409
l-arabinose isomerase (
l-AI) was cloned and overexpressed in
Lactococcus lactis using a phosphate-depletion-inducible expression system. The purified
B. longum l-AI was characterized using
d-galactose and
l-arabinose as the substrates. The enzyme was active and stable at acidic pH with an optimum at pH 6.0?C6.5. The enzyme showed the highest activity at 55?°C during a 20-min incubation at pH 6.5. The
K m value was 120?mM for
l-arabinose and 590?mM for
d-galactose. The
V max was 42?U mg
?1 with
l-arabinose and 7.7?U mg
?1 with
d-galactose as the substrates. The enzyme had very low requirement for metal ions for catalytic activity, but it was stabilized by divalent metal ions (Mg
2+, Mn
2+). The enzyme bound the metal ions so tightly that they could not be fully removed from the active site by EDTA treatment. Using purified
B. longum l-AI as the catalyst at 35?°C, equilibrium yields of 36?%
d-tagatose and 11?%
l-ribulose with 1.67?M
d-galactose and
l-arabinose, respectively, as the substrates were reached.
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