Through the fluorescence and ultraviolet-visible spectrophotometry the action of HSA was studied with the four medicines of levofloxacin hydrochloride, fleroxacin, gatifoxacin and worfloxacin, and the reasonableness of the theories and equations of fluorescence enhancement and quenching at different temperatures was compared. The result shows: at different temperatures the outcomings obtained in determining dissociation constants with such two theories can be seen effective, but the doubly reciprocal curves of quenching equation are not conformed to quenching curves based on dynamic and static quenching mechanism as those of fluorescence enhancement. For the first time energy transfer efficiency E was defined as the fluorescence intensity ratio F/F_0, where F₀ is the fluorescence intensity of free HSA and F is the fluorescence intensity after addition of medicine till no change of its intensity. It shows the maximum limit when energy transfer occurs in every system, namely no more quenching takes place while addition of more medicine to the solution. The introduction of the new definition makes the energy transfer efficiency E extend to evaluate the limit of the ability of transferring medicine by the albumin possibly.

Key words: fluorescence quenching and enhancement, human serum albumin (HSA), energy transfer efficiency, quinolone-class medicine