The genes encoding omega-laurolactam hydrolases from Cupriavidus sp. T7, Acidovorax sp. T31, Cupriavidus sp. U124, and Sphingomonas sp. U238 were cloned and sequenced. Nucleotide and amino acid sequence analysis of the four genes indicated that the primary structures of these omega-laurolactam hydrolases are significantly similar to the 6-aminohexanoate-cyclic-dimer hydrolase (EC 3.5.2.12). These genes were expressed in Escherichia coli, and the omega-laurolactam hydrolysing activity of the recombinant enzymes was compared with that of 6-aminohexanoate-cyclic-dimer hydrolase from Arthrobacter sp. KI72. The enzyme from Acidovorax sp. T31 was most successfully expressed in E. coli. Cell-free extract of the recombinant strain was used for the synthesis of 12-aminolauric acid from omega-laurolactam by "enzymatic transcrystallization," because crystalline omega-laurolactam added into the enzyme solution was converted to crystalline 12-aminolauric acid (> or =97.3% yield). Under the optimum conditions, 208 g/l of 12-aminolauric acid was produced in 17 h. The resulting pure product was identical to authentic 12-aminolauric acid.