Thermal events associated with active membrane transport in Escherichia coli

Active transport of non-metabolizable compounds by $\text{Escherichia coli}$ resulted in thermogenesis. With substrates of the lactose permease (thiomethyl galactoside, lactose) and of the glucose transport system (α-methylglucoside) the rate of heat production was largest on initial addition, but then decreased. The kinetics of heat production varied with the transport system. For the lactose transport system, more than turnover of the permease was required since heat was not produced in azide treated cells, where facilitated diffusion is known to take place. The lactose permease thermal effects are suggested to reflect operation of the energy coupling system. The thermal effects are considered to represent a useful approach in studying transport energetics and mechanisms.