Subcellular Distribution of B6 Vitamers in Cerebral Cortex

The distribution of B6 vitamers in subcellular fractions of cerebral cortex was examined. No pyridoxine and only traces of pyridoxamine could be detected in cerebral cortex. Significant quantities of pyridoxal were found in the cytoplasmic fraction. No vitamin B6 was detected in the subcellular fractions carrying microsomes, myelin, vesicles, and small membranes settling above the 1‐0 M‐sucrose gradient. Pyridoxamine phosphate was the predominant form of vitamin B6 in cerebral cortex of mature rats and guinea pigs, being present in almost twice the concentration of pyridoxal phosphate. More of the latter compound was present in the cytoplasm than in the mitochondria. In contrast, pyridoxamine phosphate was compartmentalized in extraterminal and intraterminal mitochondria. Of especial interest was the finding that there was a significant amount of pyridoxamine phosphate attached to the presynaptic membrane and a small but detectable amount in the fraction containing postsynaptic membranes.