Ionization state of pyridoxal 5′-phosphate in d-serine dehydratase, dialkylglycine decarboxylase and tyrosine phenol-lyase and the influence of monovalent cations as inferred by 31P NMR spectroscopy

Abstract

The 31P NMR spectroscopy of three pyridoxal 5′-phosphate-dependent enzymes, monomeric d-serine dehydratase, tetrameric dialkylglycine decarboxylase and tetrameric tyrosine phenol-lyase, whose enzymatic activities are dependent on alkali metal ions, was studied. 31P NMR spectra of the latter two enzymes have never been reported, their 3D-structures, however, are available. The cofactor phosphate chemical shift of all three enzymes changes by ∼3 ppm as a function of pH, indicating that the phosphate group changes from being monoanionic at low pH to dianionic at high pH. The 31P NMR signal of the phosphate group of pyridoxal 5′-phosphate provides a measure of the active site changes that occur when various alkali metal ions are bound. Structural information is used to assist in the interpretation of the chemical shift changes observed. For d-serine dehydratase, no structural data are available but nevertheless the metal ion arrangement in the PLP binding site can be predicted from 31P NMR data.