2.5. Enzyme assays
Cell-free extractswerepreparedfromwashedcellssuspended
in threevolumeof50mMphosphatebufferpH7.0bysonication
(Ultrasonicprocessor,modelXL2010)for5minandcentrifugation
at 12,000g for 45minat4 1C. Theclearsupernatantwasusedfor
further enzymaticstudies.2-Chlorobenzoate-1,2-dioxygenase
activitywasassayedspectrophotometricallyforthedetermination
of theproductcatecholat275nm.Catechol1,2-dioxygenase
activitywasassayedspectrophotometricallybymeasuringthe
increaseinabsorbanceat260nmduetotheformationof cis,cismuconic
acidaccordingto Hayaishietal.(1957). Catechol2,3-
dioxygenaseactivitywasassayedspectrophotometricallybymea-
suring theincreaseinabsorbanceat375nmduetotheformation
2-hydroxymuconicsemialdehydeaccordingto Kim etal.(1992).
Proteinwasdeterminedbythemethodof Lowry etal.(1951) using
bovineserumalbumin(BSA)asastandard.Oneunitofenzyme
activitywasdefined astheamountrequiredtocatalyzethe
formation orconsumptionof1 mmol ofproductorsubstrateper
minute.