Studies on the pyridoxal phosphate site in glycogen phosphorylase b.

It is usually accepted that the adduct formed by reaction of pyridoxal phosphate with amines in aprotic solvents is a good model to stimulate some properties of the pyridoxal phosphate site in glycogen phosphorylase. The chemical structure of this adduct was not very well established. An aldimine structure is supported by the infrared, electronic absorption and nuclear magnetic resonance spectra given in this work. Therefore, we conclude that, 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 in this paper could explain the fact that, at neutral pH, the pyridoxal phosphate can not be reduced onto phosphorylase by NaBH4.