T-2 was grown in salts medium containing intermediates of the established, inducible degradative pathway(s) for 4-toluenesulphonate/4-toluenecarboxylate. The specific activity or, if appropriate, the specific expression of pathway enzymes or their components was constant throughout growth and decreased only slowly in the stationary phase. It was found that the 4-toluenesulphonate methyl-monooxygenase system and 4-sulphobenzyl alcohol dehydrogenase (with 4-sulphobenzaldehyde dehydrogenase) were always co-induced, with similar ratios of their activities during growth with 4-toluenesulphonate, 4-toluenecarboxylate and 4-sulphobenzoate. We presume these enzymes to be co-expressed from one regulatory unit. The ratio of activities of the terephthalate 1,2-dioxygenase system to those of (1,2)-dihydroxy-1,4-dicarboxy-3,5-cyclohexadiene dehydrogenase was also constant, and present only during growth with 4-toluenecarboxylate or terephthalate. We presume these two enzymes to be co-expressed from a different regulatory unit. The oxygenase component of 4-sulphobenzoate 3,4-dioxygenase (PSBDOS) was expressed at high levels in most growth conditions examined, the exception being with 4-toluenecarboxylate as carbon source. However, no expression of a specific reductase activity linked to synthesis of the oxygenase of PSBDOS could be detected. The PSBDOS was thus active solely under conditions where the 4-toluenesulphonate methyl-monooxygenase system was also present, whose reductase is active with the oxygenase of the 4-sulphobenzoate 3,4-dioxygenase system in vitro, and, apparently, . The synthesis of PSBDOS is thus under the control of a third regulatory unit.


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