CHARACTERIZATION OF THE MALEYLACETATE REDUCTASE MACA OF RHODOCOCCUS-OPACUS 1CP AND EVIDENCE FOR THE PRESENCE OF AN ISOFUNCTIONAL ENZYME

Maleylacetate reductases (EC 1.3.1.32) have been shown to contribute n ot only to the bacterial catabolism of some usual aromatic compounds l ike quinol or resorcinol but also to the degradation of aromatic compo unds carrying unusual substituents, such as halogen atoms or nitro gro ups. Genes coding for maleylacetate reductases so far have been analyz ed mainly in chloroaromatic compound-utilizing proteobacteria, in whic h they were found to belong to specialized gene clusters for the turno ver of chlorocatechols or 5-chlorohpdroxyquinol. We have now cloned th e gene macA, which codes for one of apparently (at least) two maleylac etate reductases in the gram-positive, chlorophenol-degrading strain R hodococcus opacus 1CP. Sequencing of macA showed the gene product to b e relatively distantly related to its proteobacterial counterparts (ca , 42 to 44% identical positions). Nevertheless, like the known enzymes from proteobacteria, the cloned Rhodococcus maleylacetate reductase w as able to convert 2-chloromaleylacetate, an intermediate in the degra dation of dichloroaromatic compounds, relatively fast and with reducti ve dehalogenation to maleylacetate. Among the genes ca, 3 kb up and do wnstream of macA, none was found to code for an intradiol dioxygenase, a cycloisomerase, or a dienelactone hydrolase. Instead, the only gene which is likely to be cotranscribed with macA encodes a protein of th e short-chain dehydrogenase/reductase family. Thus, the R. opacus male ylacetate reductase gene macA clearly is not part of a specialized chl orocatechol gene cluster.