Succinate:quinone oxidoreductase (complex II) containing a single heme b in facultative alkaliphilic Bacillus sp strain YN-2000

Succinate:quinone oxidoreductase (EC 1.3.5.1) was first purified from the facultative alkaliphilic Bacillus sp, strain YN-2000 in the presence of Triton X-100. The isolated enzyme showed high succinate-ubiquinone oxidoreductase activity at pH 8.5, The K-m for ubiquinone 1 and the V-max of the enzyme were determined to be about 5 mu M and 48 mu mol of ubiquinone 1 per min per mg, respectively. The catalytic activity of the enzyme was 50% inhibited by 9 mu M 2-thenoyltrifluoroacetone or 0.8 mu M 2-n-heptyl-4-hydroxyquinoline-N-oxide. The enzyme consisted of three kinds of subunits,vith molecular masses of 66, 26, and 15 kDa, respectively, and contained 1.28 mol of covalently bound flavin adenine dinucleotide, 0.9 mol of heme b, 135 mol of menaquinone, 83 mol of nonheme iron, and 7.5 mol of inorganic sulfide per mol of enzyme. The enzyme showed symmetrical alpha absorption peaks at 556.5 and 554 nm in the reduced state at room temperature and 77 K, respectively, The potentiometric analysis of the enzyme yielded an E(m,7) of heme b of about -64 mV (n = 1), Furthermore, the content of the enzyme was increased up to fivefold when the bacterium was grown at pH 10 compared with pH 7. These results indicate that the succinate:quinone oxidoreductase with a single heme b is involved in the respiratory chain of the alkaliphile at a very alkaline pH.