4-Deoxypyridoxine 5'-phosphate is a Pyridoxal 5'-phosphate analogue and a sphingosine 1-phosphate (S1P) inhibitor. 4-Deoxypyridoxine 5'-phosphate inhibits ornithine decarboxylase activity with a Ki of 60 μM. 4-Deoxypyridoxine 5'-phosphate is a competitive inhibitor of the activation of glutamate apodecarboxylase by Pyridoxal 5'-phosphate (Ki of 0.27 μM) and strongly inhibits glutamate-dependent labeling of glutamate decarboxylase.