Activity of Na+/K+-activated Mg2+-dependent ATP-hydrolase in the cell-free extracts of the sulfate-reducing bacteria Desulfovibrio piger Vib-7 and Desulfomicrobium sp. Rod-9

The aim of our work was to study Na + /K + -activated Mg 2+ -dependent ATPase activity in cellfree extracts of the sulfate-reducing bacteria Desulfovibrio piger Vib-7 and Desulfomicrobium sp. Rod-9 isolated from the human large intestine, and to carry out the kinetic analysis of the enzyme reaction. The maximum ATPase activity for both bacterial strains at +35 oC was determined. The highest activities of the studied enzyme in the cell-free extracts of D. piger Vib-7 at pH 7.0 and Desulfomicrobium sp. Rod-9 at pH 6.5 were measured. Based on experimental data, the analysis of kinetic properties of the ATP-hydrolase reaction by the studied bacteria was carried out. The enzyme activity, initial (instantaneous) reaction rate (V 0 ) and maximum rate of the ATPase reaction (Vmax) was significantly higher in D. piger Vib-7 cells than in Desulfomicrobium sp. Rod9. Michaelis constants (K m ) of the enzyme reaction for both bacterial strains were determined. ATPase activity, hydrogen sulfide, intestinal microbiocenosis, bowel diseases, ulcerative colitis Sulfate-reducing bacteria carry out the dissimilatory sulfate reduction during anaerobic respiration (Barton and Hamilton 2007). The final product of the sulfate reduction in the human intestine is hydrogen sulfide which is carcinogenic to its cells, and can cause inhibition of cytochrome oxidase, colonocytes oxidation of butyrate, destruction of epithelial cells, development of ulcers, and inflammation with subsequent development of colon cancer (Pitcher and Cummings 1996; Gibson et al. 1991; Cummings et al. 2003). The transport of sulfate ions and organic compounds in the cytoplasm of the bacterial cells occurs through active transport using ATP energy (Barton and Hamilton 2007). In this regard, it is very important to study the mechanisms of sulfate ions transport, enzymatic activity and kinetic properties of other ATP-dependent enzymes of sulfatereducing bacteria from human intestine. Plentiful data are available on the functions of biological membranes including the integral membrane protein ATP-dependent systems of transport ions (Lodish et al. 2000; Yuan et al. 2005; Tian et al. 2006). However, the ATPase activity of the sulfate-reducing bacteria Desulfovibrio piger and Desulfomicrobium sp. isolated from the human large intestine has not been studied yet. A comprehensive study of the functioning and role of Na + /K + -pump as a system of energy-dependent transport of different ions in the regulation of the dissimilatory sulfate reduction and accumulation of hydrogen sulfide will enable to form a holistic view on the participation of these systems in maintaining ion homeostasis of the sulfate-reducing bacteria cells.