Lu 9405690 One of the major reduced inorganic sulfur compounds present in nature, thiosulfate is used by thiobacilli and other chemolithotrophic sulfur-oxidizing bacteria as energy source for growth and for CO2 incorporation into cell material. The activities of these bacteria have long been recognized to play a vital role in the oxidative phase of the global sulfur cycle and for this reason have also been used in industry to breakdown sulfide minerals. Thiosulfate utilization occurs via a thiosulfate-oxidizing multienzyme complex (TOMC) which catalyzes complete oxidation of thiosulfate to sulfate with a c-type cytochrome and water. TOMC consists of four essential components: components A and B, cyt c551, and cyt c552.5. TOMC is the first purified enzyme system involved in the oxidation of reduced inorganic sulfur (other than sulfite) to sulfate. The objectives of the present research are to: 1) determine the reaction pathway and putative intermediate(s) formed in the oxidation reaction; 2) determine the role(s) of components A and B; 3) characterize the multiple hemes in the c-type components, and understand how electrons derived from thiosulfate oxidation are transferred through these hemes; and 4) determine the structure and function of the manganese cluster in component B. A major outcome of the research will be to determine the metabolic pathway for the conversion of thiosulfate to sulfate. The work is valuable to our understanding of this unique mode of life in nature, and it will contribute substantially to our knowledge about sulfur biochemistry, microbial metabolism and evolution, and enzymology. %%% Bacteria such as thiobacilli utilize reduced inorganic sulfur compounds, such as sulfur, sulfide and thiosulfate, as their energy source for growth. These cells play an essential role in the global sulfur cycle. For practical purposes, the bacteria have been used in industry to breakdown sulphide minerals in microbioleaching processes to recover cop per, uranium, gold and nickel. Significant progress has recently been made in our understanding of the physiology and bioenergetics of sulfur oxidation. The thiosulfate-oxidizing multienzyme complex from Thiobacillus versutus is the only purified and characterized enzyme system to date, which catalyzes the complete oxidation of thiosulfate to sulfate. It provides a unique system to reveal the enzymology of thiosulfate (sulfur) oxidation This work is valuable to our understanding about this unusual mode of life. It will contribute to knowledge about sulfur biochemistry, microbial metabolism and evolution, and enzymology. The studies may help to develop improved industrial methods for using sulfur-oxidizing bacteria in large-scale bioleaching and desulfurization processes. ***
