lin-Benzo-ATP and-ADP: Versatile fluorescent probes for spectroscopic and biochemical studies.

lin-Benzo-adenine nucleotides can act not only as probes for fluorescence studies but also as structural active site probes for enzymes. To understand the basic properties oflin-benzo-ATP and-ADP, protolysis and Mg(2+) and Ca(2+), binding are investigated between pH 6.2 and pH 8.5 by spectrophotometric and spectrofluorometric titrations. Based on a reaction model, a set of equilibrium constants is determined which is consistent with all available experimental results. The pK values of the Mg(2+) and Ca(2+) complex oflin-benzo-ATP in the chosen medium are 4.6 and 4.1, respectively, and those for the corresponding diphosphate are 3.1 and 2.8, respectively. Fluorescence and absorption spectra are reported.