Abstract
Pyridoxal 5'-phosphate inhibited the binding to DNA-cellulose of the 1,25-dihydroxyvitamin D_3 receptor extracted from hen intestinal chromatin. Pyridoxal and pyridoxamine 5'-phosphate did not show this potency. The inhibition by pyridoxal 5'-phosphate of the binding of the receptor to DNA-cellulose was reversibly restored by isonicotinic acid hydrazide, which can function as a pyridoxal 5'-phosphate scavenger through formation of pyridoxal hydrazone. The inhibitory action of pyridoxal 5'-phosphate, however, changed into an irreversible fashion after reduction of the pyridoxal 5'-phosphate-treated chromatin extract. These results suggest that the pyridoxal 5'-phosphate action on the 1,25-dihydroxyvitamin D_3 receptor involves formation of Schiff base between this active vitamin B_6 and ε-amino group of lysine. Also participation of the lysyl residue to the DNA-binding of the receptor is discussed.
