MOLECULAR MECHANISMS OF BIOCATALYTIC DESULFURIZATION OF FOSSIL-FUELS

The development of biocatalytic desulfurization of petroleum fractions may allow its use in place of conventional hydrodesulfurization (HDS) . Dibenzothiophene (DBT) is representative of a broad range of sulfur heterocycles found in petroleum that are recalcitrant to desulfurizati on via HDS. Rhodococcus sp. strain IGTS8 has the ability to convert DB T to 2-hydroxybiphenyl (HBP) with the release of inorganic sulfur. The conversion of DBT to HBP is catalyzed by a multienzyme pathway consis ting of two monooxygenases and a desulfinase. The final reaction catal yzed by the desulfinase appears to be the rate limiting step in the pa thway. Each of the enzymes has been purified to homogeneity and their kinetic and physical properties studied. Neither monooxygenase has a t ightly bound cofactor and each requires an NADH-FMN oxidoreductase for activity. An NADH-FMN oxidoreductase has been purified from Rhodococc os and is a protein of approximately 25,000 molecular weight with no a pparent sequence homology to any other protein in the databases. We de scribe a unique sulfur acquisition system that Rhodococcus uses to obt ain sulfur from very stable heterocyclic molecules.