[Effect of pH on tryptophan fluorescence of phosphorylase kinase].

The influence of pH on tryptophane residues in phosphorylase kinase was determined by iodide quenching of tryptophan fluorescence. The experiments were carried out in the pH range of 6 to 10 and the results were presented in a modified Stern--Volmer plot. It was found that the fraction accessible to the quencher was smaller at pH 6 and increased at basic pH of the solution. The results correlated with the enzymatic activity and were interpreted as a structural change in the enzyme molecule. The polarized fluorescence measurements indicated that some aggregate processes proceeded together with the decrease of pH under 7.