The assay for phenol hydroxylase (EC 1.14.13.7) was
conducted spectrophotometrically by monitoring absorbance
decrease at 340 nm, as described by Jones et al. [5]. Spectrophotometric
measurements were recorded every 15 s for
2 min at room temperature. Catechol 1,2-dioxygenase (EC
1.14.13.1) and catechol 2,3-dioxygenase (EC 1.13.11.2) activities
were measured spectrophotometrically by following
formation of ciscis-muconic acid at 260 nm [8] and of
2-hydroxymuconic semi-aldehyde at 375 nm [9], respectively.
Readings were taken at 30 s intervals for 5 min at
room temperature. Controls without substrate or extract were
prepared for each assay. One enzyme unit was defined as
the amount of enzyme that catalyzes the consumption of 1
mol co-substrate or formation of 1 mol product per min.
Protein concentration in the cell extract was determined by
the method of Bradford [10] using bovine serum albumin as
the standard. Specific activity was defined as Units mg per
protein.