Effects of site-directed mutagenesis of protolytic residues in subunit I of Bacillus subtilis aa3-600 quinol oxidase. Role of lysine 304 in proton translocation.

Various protolytic residues in subunit I of aa3-600 quinol oxidase of the aerobic Gram-positive Bacillus subtilis were mutagenized to nonpolar residues. Two of the mutations, Y284F and K304L, impaired the bioenergetic function of the microorganism. The Y284F mutation suppressed the electron-transfer activity of quinol oxidase and altered its interaction with CO and H2O2, thus showing destruction of the binuclear domain as observed for the bo3 quinol oxidase of Escherichia coli. The K304L mutation did not alter significantly the redox activity of the oxidase and its interaction with CO and H2O2 but suppressed the proton pumping activity of the enzyme. These results show that the K304 residue, which is invariantly conserved (as K or R) in practically all the sequences of the heme-copper oxidases so far available (around 100), is essential for the proton pumping activity of the oxidase.