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

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Abstract
The ability of pyridoxal 5''-phosphate to inhibit DNA-cellulose binding of activated glucocorticoid-receptor complexes [rat liver] is pH and protein concentration dependent. At the tested pH, 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 DEAE-cellulose or 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 and an inhibitory effect on the binding of activated complexes to DNA-cellulose.

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