Van Berkel W J, Müller F
Department of Biochemistry, Agricultural University, Wageningen, The Netherlands.
Eur J Biochem. 1989 Feb 1;179(2):307-14. doi: 10.1111/j.1432-1033.1989.tb14556.x.
The free and complexed flavoprotein, p-hydroxybenzoate hydroxylase, was studied by light-absorption, circular-dichroism and fluorescence techniques as a function of the pH. The following compounds served as ligands for the enzyme: p-hydroxybenzoate, p-fluorobenzoate, benzoate, p-aminobenzoate and tetrafluoro-p-hydroxybenzoate. Depending on the technique used, the various ligands exhibit pH-dependent physical properties and dissociation constants. The data can be fitted with pKa values in the range 7.7-7.9. It is suggested that this pKa value belongs to a tyrosine residue in the active center of the enzyme. This assignment is supported by published data and additional experiments.
