Epoxides and ketones are widely used in industry and have been shown to have potential mutagenic, carcinogenic, and toxic effects. Therefore, there is considerable interest in microbial based bioconversions of these compounds into less environmentally detrimental compounds. Epoxides are utilized in a variety of industrial processes as intermediates in organic synthesis. Due to the strained three-membered ring structure of these compounds, epoxides react readily with a number of nucleophiles {Swaving, 1998 #1315}. Optically pure epoxides are intermediates in the synthesis of a number of bioactive compounds including leukotrienes, pheromones, antibiotics, and an HIV protease inhibitor. Due to the reactive nature of these compounds and their ability to react with cellular components including DNA and proteins, they are of considerable concern as potential human health hazards. The ability of epoxides to form covalent adducts to DNA can result in mutagenic and carcinogenic effects. Acetone is a toxic molecule that is synthesized industrially and formed biologically during bacterial fermentation and mammalian starvation. A number of bacteria are able to grow with acetone as a source of carbon and energy. In addition, acetone is formed as an intermediate in the metabolism of propane and isopropanol by some bacteria. Bacterial pathways of acetone metabolism and the biochemical properties of acetone-metabolizing enzymes are poorly understood. The widespread use of epoxides and ketones has resulted in an increased interest in the mechanisms by which various microorganisms transform these compounds into less environmentally detrimental compounds. From a basic science standpoint the bioconversions we propose to study represent novel microbial based CO2 fixation / carboxylation mechanisms that have only recently been identified. The results obtained in the study will reveal new insights into these novel carboxylation reactions and will provide the basis for the comparison of the mechanism of these interesting enzymes to other more well characterized CO2 fixing and carboxylating enzymes.