Pyridoxine-derived B sub(6) vitamers and pyridoxal 5'-phosphate-binding proteins in cytosolic and nuclear fractions of HTC cells

The nuclear fraction of rat hepatoma-derived HTC cells contained approximately 8% of the total cellular pyridoxal 5'-phosphate. HTC cells were able to metabolize ( super(3)H)pyridoxine to coenzymatically active pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate. With the aid of a monoclonal antibody specific for the 5'-phosphopyridoxyl group, it was shown that there was one major pyridoxal 5'-phosphate-binding protein in a sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)-resolved nucleoplasmic extract of HTC cells. Isoelectric focusing followed by SDS-PAGE also indicated the presence of one major pyridoxal 5'-phosphate-binding protein in the nucleoplasmic extract of HTC cells having a relatively high isoelectric point (approximately 7). Data were obtained indicating that the protein might exist in a higher molecular weight form, probably a dimer. Currently, these findings constitute virtually all of the available information on vitamin B sub(6) and the cell nucleus.