Probable nitrate/nitrite antiporter that may be involved in nitrate import and nitrite export during anaerobic growth. nitrate(in) + nitrite(out) = nitrate(out) + nitrite(in) Mutation has minor effects on the ability to grow anaerobically. In contrast, narK1/narK2 double mutant is unable to grow anaerobically. Belongs to the major facilitator superfamily. Nitrate/nitrite porter (TC 2.A.1.8) family.