Leptospira interrogans, a Gram-negative pathogen, could cause infections in a wide variety of mammalian hosts, but due to their fastidious cultivation requirements and the lack of genetic systems, the pathogenic factor is still not clear. Isocitrate dehydrogenase (IDH) is a key enzyme in the tricarboxylation (TCA) cycle, which could have an important impact on the growth and pathogenesis of the bacteria. In the present study, we first report the cloning, heterologous expression, and detailed characterization of the IDH gene from L. interrogans serovar Lai strain 56601(LiIDH). The molecular weight of LiIDH was determined to be 87 kDa by filtration chromatography, suggesting LiIDH is a typical homodimer. The optimum activity of LiIDH was found at 60 A degrees C, and its optimum pH was 7.0 (Mn2+) and 8.0 (Mg2+). Heat inactivation studies showed that heat treatment for 20 min at 50 A degrees C caused a 50 % loss of enzyme activity. LiIDH was completely divalent cation dependent as other typical dimeric IDHs and Mg2+ was its best activator. The recombinant LiIDH specificities (k (cat)/K (m) values for NADP(+) and NAD(+)) in the presence of Mg2+ and Mn2+ were 6,269-fold and 1,000-fold greater for NADP(+) than NAD(+), respectively. This current work is expected to shed light on the functions of metabolic enzymes in L. interrogans and provide useful information for LiIDH to be considered as a possible candidate for serological diagnostics and detection of L. interrogans infection.