TIME-RESOLVED INTRINSIC FLUORESCENCE OF ENZYME-I - THE MONOMER DIMER TRANSITION

Enzyme I of the bacterial phosphotransferase system can exist in a monomer/dimer equilibrium which may have functional significance. Each monomer contains two tryptophan residues. It is demonstrated that the decay of both the monomer and the dimer can be described by a biexponential. The decay times depend on the temperature and at 6-degrees-C the decay times are tau1 = 0.4 ns and tau2 = 3.2 ns for the monomer and tau3 = 3.2 ns and tau4 = 7.2 ns for the dimer form of the enzyme. The changes in the fluorescence decay parameters can be utilized to measure the equilibrium constant for the monomer/dimer transition.