FIGURE 1.

Schematic representation of ATP synthesis in the SMP and SBP systems. A, the NADH:O₂ reaction drives proton translocation by complexes I, III, and IV ((n + 6) H⁺ per NADH). B, the NADH:Q₁ reaction drives proton translocation by complex I (n H⁺ per NADH); complexes III and IV are inhibited. C, the succinate:O₂ reaction drives proton translocation by complexes II, III, and IV (6 H⁺ per succinate). The number of protons required to synthesize 1 ATP is 2.7 in B. taurus and 4 in P. denitrificans.