CHARACTERISATION OF A CHROMOSOMALLY ENCODED CATECHOL 1,2-DIOXYGENASE (EC 1.13.11.1) FROM ALCALIGENES EUTROPHUS CH34

摘要

Alcaligenes eutrophus CH34 used benzoate as a sole source of carbon and energy, degrading it through the 3-oxoadipate pathway. All the enzymes required for this degradation were shown to be encoded by chromosomal genes. Catechol 1,2-dioxygenase activity was induced by benzoate, catechol, 4-chlorocatechol, and muconate. The enzyme is most likely a homodimer, with an apparent molecular weight of 76,000 +/- 500. According to several criteria, its properties are intermediate between those of catechol 1,2-dioxygenases (CatA) and chlorocatechol 1,2-dioxygenases (ClcA). The determined K-m for catechol is the lowest among known catechol and chlorocatechol dioxygenases. Similar K-m values were found for para-substituted catechols, although tile catalytic constants were much lower. The catechol 1,2-dioxygenase from strain CH34 is unique in its property to transform tetrachlorocatechol; however, excess substrate led to a marked reversible inhibition. Some meta- and multi-substituted catechols behaved similarly. The determined K-m (Or K-i) values for para- or meta-substituted catechols suggest that the presence of an electron-withdrawing substituent at one of these positions results in a higher affinity of the enzyme for the Ligand. Results of studies of recognition by the enzyme of various nonmetabolised aromatic compounds are also discussed. [References: 37]