The synthesis of melatonin in Xenopus retinas, chick and quail retinal cell cultures, and Y79 human retinoblastoma cells is stimulated by cAMP through a protein synthesis-dependent mechanism. In Y79 retinoblastoma cells, combined treatment with the RNA synthesis inhibitor camptothecin and agents that elevate cAMP, such as forskolin, causes a synergistic elevation of melatonin. Using two-dimensional gel analysis we have identified a 30 kDa cytosolic protein (p30) whose radiolabeling was consistently increased in parallel with increases in arylalkylamine N-acetyltransferase activity and melatonin production that were induced by forskolin and/or camptothecin. Pulse-chase experiments suggest that the elevation in radiolabeling of p30 is due to increased synthesis. Three candidate proteins found in the mammalian pineal, protein 14-3-3, malate dehydrogenase, and recoverin, do not comigrate with p30.
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Janavs et al. (1995) studied this question.