REGULATION OF TRYPTOPHAN-HYDROXYLASE BY CYCLIC-AMP, CALCIUM, NOREPINEPHRINE, AND LIGHT IN CULTURED CHICK PINEAL CELLS

The level of S-35 incorporation into tryptophan hydroxylase (TPH) show s a circadian rhythm in cultured chick pineal cells, The TPH oscillati on peaks in the early subjective night, persists in constant darkness, and can be phase shifted by light, in parallel to the effect of those treatments on melatonin synthesis, Using quantitative two-dimensional polyacrylamide gel electrophoresis, we have examined the regulation o f TPH by agents known to affect melatonin synthesis in the chick pinea l, We report here that S-35 incorporation into TPH is induced by cycli c AMP and calcium, and partially inhibited by acute exposure to light, Cyclic AMP also causes a proportional increase in the radiolabeling o f one of the TPH isoforms and a concomitant decrease in another isofor m, possibly reflecting a change in the phosphorylation state of TPH. T his effect is reversed by treatments known to reduce intracellular cyc lic AMP levels in the chick pineal, Cyclic AMP thus appears to be invo lved in both translational and posttranslational process regulating th e expression of TPH in chick pineal cells.