Simultaneous analysis of single-photon timing data for the one-step determination of activation energies, frequency factors and quenching rate constants. Application to tryptophan photophysics

A general global analysis of single-photon timing data is presented in which each fluorescence decay curve can be described by a different decay law. The model parameters can be held in common within one curve and/or between related curves. Any or all parameters can be kept fixed, or they may be variable to seek optimum values. This general analysis allows the determination of activation energies, frequency factors and quenching rate constants in one step. The construction of the global mapping table which relates parameters in one experiment to those in another is explained in detail. The use and performance of this general simultaneous analysis are examined using tryptophan fluorescence decays at pH 6.0 obtained at various emission wavelengths as a function of temperature and added solute quencher. The results show that tryptophan at pH 6.0 decays as a biexponential with decay times which are independent of the analysis wavelength. The decay component with the short lifetime has a deactivation rate constant of 1.4 x 10(9) s-1 independent of temperature. The decay component with the long lifetime has an activation energy of 28 kJ/mol and a frequency factor of 3 x 10(13) s-1; its temperature-independent decay rate constant equals 1 x 10(8) s-1. Recursion formulas for a computer program to estimate activation energies, frequency factors, and decay rate constants are provided.     

Effects of phorbol 12-myristate 13-acetate and cortisol interaction on steroid-binding capacity in the rat.

The specificity of the cortisol-receptor protein is examined in plasma and liver cytosol of rats. Phorbol 12-myristate 13-acetate does not inhibit the binding of cortisol to transcortin, nor does it affect the binding capacity of dexamethasone to the intracellular glucocorticoid receptor, but, by interacting with the cortisol molecule, it interferes with hormone-mediated processes in the cell.