Kinetic Study of the Sulfite Dehydrogenase-catalyzed Reaction in the Subcellular State of Thiobacillus thiooxidans

Abstract

Based on kinetic studies of the sulfite dehydrogenase-catalyzed reaction investigated using the subcellular fraction instead of the microbe Thiobacillus thiooxidans, it was confirmed that the initial velocity is very proportional on the concentration of the subcellular fraction and the optimal pH is 7.5, which is the same as that obtained in the microbe. The kinetic parameters, Michaelis constant (Km) and maximum velocity (V), were evaluated to be 1.7±0.2 mM and 0.083±0.035 mM/min/mg protein, respectively. The ferricyanide concentration examined was found to be proportional to the initial velocity within 1.5 mM. It was also found that cytochrome c can be absorbed as a second substrate in place of ferricyanide. Thus, a new device should be very possible using the subcellular fraction of T. thiooxidans as a highly sensitive and automatic sensor apparatus for sulfite etermination.