Oxidation of butyrate with TTC in cell suspensions of butyrate-grown, Percoll-separated S. wolfei cells. Shown are the concentrations of acetate and formazan. Open symbols, formazan concentration; filled symbols, acetate concentration. Circles, no inhibitor added; triangles, cell suspensions containing 0.1 mM TPZ; squares, negative control without butyrate (n = 3, mean values ± the standard deviation are indicated).