The purification and characterisation of 4-chlorobenzoate:CoA ligase and 4-chlorobenzoyl CoA dehalogenase from Arthrobacter sp. strain TM-1

Abstract

4-Chlorobenzoate:CoA ligase, the first enzyme in the pathwayfor 4-chlorobenzoate dissimilation, has been partially purifiedfrom Arthrobacter sp. strain TM-1, by sequential ammoniumsulphate precipitation and chromatography on DEAE-Sepharoseand Sephacryl S-200. The enzyme, a homodimer of subunitmolecular mass approximately 56 kD, is dependent onMg²⁺-ATP and coenzyme A, and produces 4-chlorobenzoyl CoA and AMP. Besides Mg²⁺, Mn²⁺, Co²⁺, Fe²⁺ and Zn²⁺ are also stimulatory, but not Ca²⁺. Maximal activity is exhibited at pH 7.0 and 25 °C. The ligase demonstrates broad specificity towards otherhalobenzoates, with 4-chlorobenzoate as best substrate.The apparent Michaelis constants (K_m) of the enzymefor 4-chlorobenzoate, CoA and ATP were determined as3.5, 30 and 238 μM respectively. 4-ChlorobenzoylCoA dehalogenase, the second enzyme, has been purified tohomogeneity by sequential column chromatography onhydroxyapatite, DEAE-Sepharose and Sephacryl S-200. It isa homotetramer of 33 kD subunits with an isoelectric pointof 6.4. At pH 7.5 and 30 °C, K_m andk_cat for 4-CBCoA are 9 μM and1 s^-1 respectively. The optimum pH is 7.5, andmaximal enzymic activity occurs at 45 °C. Theproperties of this enzyme are compared with those ofthe 4-chlorobenzoyl CoA dehalogenases from Arthrobactersp. strain 4-CB1 and Pseudomonas sp. strain CBS-3, whichdiffer variously in their N-terminal amino acid sequences, optimalpH values, pI values and/or temperatures of maximal activity.