PLP to monitor phosphorylase turnover

Beynon, R.J., Leyland, D.M., Evershed, R.P., Edwards, R.H.T. & Coburn, S.P. (1996) Measurement of the turnover of glycogen phosphorylase by gas chromatography/mass spectrometry using stable isotope derivatives of pyridoxine (Vitamin B6) Biochem J 317, 613-619 [PUBMED] [PDF]

The majority of vitamin B6 in the body is in skeletal muscle, bound as the cofactor pyridoxal 5'-phosphate to one abundant protein, glycogen phosphorylase. Previous work has established that radiolabelled vitamin B6 can be used as a turnover label for glycogen phosphorylase. In this study, a stable isotope derivative of pyridoxine {dideuterated pyridoxine; 3-hydroxy-4-(hydroxymethyl) -5-[hydroxymethyl-2H2]-2-methylpyridine} ([2H2]PN) has been used as a metabolic tracer to study the kinetics of labelling of the body pools of vitamin B6 in mice. A non-invasive method was developed in which the isotope abundance of the urinary excretory product of vitamin B6 metabolism, 4-pyridoxic acid, was analysed by GC/MS. The change in isotope abundance of urinary 4-pyridoxic acid following administration of [2H2]PN reflects the kinetics of labelling of the body pools of vitamin B6, and yields, non-invasively, the rate of degradation of glycogen phosphorylase.