Changes in the intracellular levels of pyridoxal 5'-phosphate affect the induction of tyrosine aminotransferase by glucocorticoids

In the present study a cell culture system was used to correlate the intracellular levels of pyridoxal 5′-phosphate with the induction of the hepatic enzyme, tyrosine aminotransferase, by glucocorticoids. Increased intracellular levels of pyridoxal 5′-phosphate produced antiglucocorticoid effects whereas a reduction in pyridoxal 5′-phosphate content increased the sensitivity of cells to glucocorticoids. The data strongly implicate pyridoxal 5′-phosphate as an $\text{in}\text{vivo}$ modulator of the glucocorticoid receptor. The mechanism by which pyridoxal 5′-phosphate modulates the receptor is presumably through its binding to the DNA-binding site of the “activated” form of the receptor complex.