A synaptosomal preparation from mouse brain transported gamma-hydroxyb
utyric acid in a manner displaying saturation kinetics. A K-t of 48 +/
- 11 mu M was calculated. In the presence of pyridoxal 5'-phosphate, u
ptake was markedly enhanced. Stimulation of uptake was observed with i
ncreasing concentrations of pyridoxal 5'-phosphate, up to a maximum of
about 3.5 mM. Increasing concentrations above this value led to a ste
ady decrease in the stimulation of uptake, till at 7 mM pyridoxal 5'-p
hosphate and above there was a noticeable inhibition of uptake. The pr
esence of increasing concentrations of gamma-hydroxybutyric acid gradu
ally reduced the amount of stimulation, thus pyridoxal 5'-phosphate ap
peared to be producing its effect by reducing the K-t of the transport
system rather than increasing its V-max.