We previously identified
vitamin B6 deficiency in a child presenting with
seizures whose primary diagnosis was the inherited disorder
hyperprolinemia type II. This is an unrecognized association, which was not explained by diet or medication. We hypothesized that
pyridoxal phosphate (
vitamin B6 coenzyme) was de-activated by L-Delta(1)-pyrroline-5-carboxylic
acid, the major intermediate that accumulates endogenously in
hyperprolinemia type II. The proposed interaction has now been investigated in vitro with high resolution 1H nuclear magnetic resonance spectroscopy and mass spectrometry at a pH of 7.4 and temperature of 310 K. Three novel adducts were identified. These were the result of a Claisen condensation (or Knoevenagel type of reaction) of the activated C-4
carbon of the
pyrroline ring with the
aldehyde carbon of
pyridoxal phosphate. The structures of the adducts were confirmed by a combination of high performance liquid chromatography, nuclear magnetic resonance, and mass spectrometry. This interaction has not been reported before. From preliminary observations, pyrroline-5-carboxylic
acid also condenses with other aromatic and aliphatic
aldehydes and
ketones, and this may be a previously unsuspected generic addition reaction. Pyrroline-5-carboxylic
acid is thus found to be a unique endogenous
vitamin antagonist.
Vitamin B6 de-activation may contribute to
seizures in
hyperprolinemia type II, which are so far unexplained, but they may be preventable with long term
vitamin B6 supplementation.