Dual effects f pyridoxal 5'-phosphate on glucocorticoid-receptor complexes

The ability of pyridoxal 5'-phosphate to inhibit DNA-cellulose binding of activated glucocorticoid-receptor complexes is pH and protein concentration dependent. At the tested pHs, all of the inhibitory activity of pyridoxal 5'- phosphate appears to be due to its ability to form a Schiff base. 2-Amino-2-(hydroxymethyl)-1,3-propanediol (100 mM) is unable to prevent or reverse the pyridoxal 5'-phosphate mediated inhibition of DNA-cellulose binding, while the same concentration of lysine is partially effective. Pyridoxal 5'-phosphate does not alter the elution profile of glucocorticoid-receptor complexes as ascertained by diethylaminoethyl (DEAE)-cellulose of DEAE-Sephadex chromatography. This observation permitted the use of these resins in detecting the previously unreported stimulation of glucocorticoid-receptor complex activation by pyridoxal 5'-phosphate. This stimulation is specific for pyridoxal 5'-phosphate and appears to be mediated via a Schiff base formation. Additionally, glucocorticoid-receptor complexes activated by pyridoxal 5'-phosphate treatment at low temperatures do not differ in size from thermally activated complexes. Thus, in vitro, pyridoxal 5'-phosphate can exert both a stimulatory effect on activation as well as an inhibitory effect on the binding of activated complexes to DNA-cellulose.