[Cloning and expression of catA gene from Pseudomonas putida ND6 and study on the catechol cleavage pathway]

Catechol 1,2-dioxygenase gene, calA, from naphthalene-degrading plasmid pND6-1 of Pseudomonas putida ND6, was cloned and expressed in Escherichia coli. Enzymic properties of the expressed product were investigated. The results indicated that the Km and Vmax of the enzyme are 0.019 mol/L and 1.434 mol/(min x mg), respectively. The enzyme possessed a thermal stability and 93.7% activity was retained after incubating at 50 degrees C for 45 min. Fe2+ could enhance the enzyme activity by 292%. The enzyme displayed a lower activity against 4-chlorocatechol and belongs to group I of catechol 1,2-dioxygenases. When naphthalene was used as a substrate for growth of strain ND6, catechol 1, 2-dioxygenase and catechol 2,3-dioxygenase activities were both detected in their crude extract. However, when strain ND6 was grown on benzoate, rho-hydroxybenzoic acid or phenylacetic acid as a sole source of carbon the activity of catechol 1,2-dioxygenase was much higher than that of catechol 2,3-dioxygenase. These indicated that strain ND6 is able to metabolize naphthalene by catechol meta- and ortho-cleavage pathways. When benzoate, rho-hydroxybenzoic acid and phenylacetic acid were used as growth substrates, strain ND6 degrades these compounds only by catechol ortho-cleavage pathway.