The effect of changes in cellular energy state on 6[C-14]glucose uptake and activity of the phosphoenolpyruvate:glucose phosphotransferase system (PTS) in Brevibacterium flavum RC 115 cells was investigated. Energy generation in cells was varied by adding an inhibitor of cellular respiration (potassium cyanide) and an uncoupler of oxidative phosphorylation (pentachlorophenol) to the cell culture as well as by changing thiamine concentration in the bacterial growth medium. The results showed that glucose uptake in ＇respiring＇ cells was inversely correlated with bacterial respiration activity: uptake declined with excess ATP generation and increased with lower ATP synthesis caused by electron transport inhibitors and uncouplers. Glucose PTS activity was also inversely correlated with cellular pyruvate kinase activity and the intracellular concentration of pyruvate. It was concluded that glucose PTS activity in B. flavum RC 115 cells was controlled by ATP generation in cells and, probably, by the intracellular concentration of pyruvate. (C) 2000 Elsevier Science Ltd. All rights reserved.