Purification and characterization of a cold-adapted isocitrate lyase and expression analysis of the cold-inducible isocitrate lyase gene from the psychrophilic bacterium Colwellia psychrerythraea

Isocitrate lyase (ICL) from Colwellia psychrerythraea, a psychrophilic bacterium, was purified and characterized. The subunit molecular mass was 64 kDa, which is larger than that of other bacterial ICLs. The optimal temperature for its activity was 25degreesC, the value of K-m for the substrate (DL-isocitrate) was minimum at 15degreesC, and the catalytic efficiency (k(cat)/K-m) value was maximum at 20degreesC. Furthermore, the enzyme was remarkably thermolabile and completely inactivated by incubation for 2 min at 30degreesC. These features indicate that ICL from this bacterium is a typical cold-adapted enzyme. A partial amino acid sequence of the C. psychrerythraea ICL was very similar to that of the closely related psychrophile Colwellia maris. Expression of the gene encoding the C. psychrerythraea ICL was found to be induced by low temperatures and by acetate in the medium. The cold adaptation of the catalytic properties of ICL and the stimulated expression of its gene at low temperatures strongly suggest that this enzyme is important for the growth of this bacterium in a cold environment.