STIMULATION OF MOUSE-BRAIN GAMMA-HYDROXYBUTYRIC ACID TRANSPORT BY PYRIDOXAL 5'-PHOSPHATE

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.