An F-1-ATPase-defective mutant of Escherichia coil K-12, strain TBLA-1, showing an enhanced pyruvic acid productivity compared with its parental strain W1485lip2, was characterized physiologically to elucidate the mechanisms of the enhancement in productivity. Cells of strain TBLA-1 producing pyruvic acid showed a higher rate of the oxygen consumption and a higher b-type cytochromes content than cells of strain W1485lip2. The activities of the phosphotransferase system for glucose uptake measured in terms of the level of phosphoenolpyruvate-dependent phosphorylation of methyl alpha-D-glucopyranoside and 2-deoxy-D-glucose using toluenized cells were higher in strain TBLA-1 than in strain W1485lip2. Among the activities of all the glycolytic enzymes, those of phosphoglycerate kinase and pyruvate kinase-I were found to be higher in strain TBLA-1 than in strain W1485lip2 during the logarithmic growth phase. These characteristics of strain TBLA-1 are discussed in relation to its enhanced pyruvic acid productivity.