Studies on the Pyridoxal Phosphate Site in Glycogen Phosphorylase b

Abstract
The adduct formed by reaction of pyridoxal phosphate with amines in aprotic solvents is considered a good model to simulate some properties of the pyridoxal phosphate site in [rabbit muscle] glycogen phosphorylase [.alpha.-1,4-glucan:orthophosphate glucosyltransferase EC 2.4.1.1]. The chemical structure of this adduct was not well established. An aldimine structure is supported by the infrared, electronic absorption and NMR spectra reported. Therefore, at neutral pH, the pyridoxal phosphate is bound to the glycogen phosphorylase through a Schiff base structure and embedded in a hydrophobic environment. The polarographic measurements reported could explain the inability of the pyridoxal phosphate to be reduced onto phosphorylase by NaBH4 at neutral pH.