* To whom correspondence should be addressed.
Received May 21, 2009; Revision received June 23, 2009
In this work, high ΔµH+-dependent succinate oxidase activity has been demonstrated for the first time with membrane vesicles isolated from Bacillus subtilis. The maximal specific rate of succinate oxidation by coupled inside-out membrane vesicles isolated from a B. subtilis strain overproducing succinate:menaquinone oxidoreductase approaches the specific rate observed with the intact cells. Deenergization of the membrane vesicles with ionophores or alamethicin brings about an almost complete inhibition of succinate oxidation. An apparent Km for succinate during the energy-dependent succinate oxidase activity of the vesicles (2.2 mM) is higher by an order of magnitude than the Km value measured for the energy-independent reduction of 2,6-dichlorophenol indophenol. The data reveal critical importance of ΔµH+ for maintaining active electron transfer by succinate:menaquinone oxidoreductase. The role of ΔµH+ might consist in providing energy for thermodynamically unfavorable menaquinone reduction by succinate by virtue of transmembrane electron transport within the enzyme down the electric field; alternatively, ΔµH+ could play a regulatory role by maintaining the electroneutrally operating enzyme in a catalytically active conformation.
KEY WORDS: succinate:menaquinone oxidoreductase, ΔµH+, Bacillus subtilis, electrogenesis, menaquinone, fumarate