the effect of pressure on the molecular complex of isoalloxazine and adenine the effect of pressure to 10 kilobars on the fluorescence characteristics of flavin mononucleotide fmn flavinadenine dinucleotide fad and on complexes of fmn with adenylic acid amp and with i has been studied the properties measured include peak location fluorescence yield and lifetime from these results the equilibrium constant k and the rate constant k for complex formation were evaluated as a function of pressure the pressure dependence of these coefficients shows that the volume of the system decreases upon complex formation and that there is an expansion upon formation of the activated complex deltavdouble dagger is positive the implications of these results for protein denaturation are mentioned