Defense of Cutaneous Cells Against Uv Irradiation. I. Photomediated Binding of Trimethyl Psoralen to Dna of Melanoma Cells in Culture

Pigmented and nonpigmented murine melanoma cells in culture were irradiated with ultraviolet light (365 nm) in the presence of tritiated trimethyl psoralen (3H TMP) and cellular DNA was extracted. For each cell type, regardless of the presence of pigment, the rates of covalent binding of 3H TMP to DNA and the saturation points reached were the same. The formation by irradiation of both monofunctional and bifunctional (cross-linking) adducts of TMP with cellular DNA was demonstrated by the resistance to enzymic and chemical hydrolysis of the DNA-3H TMP complex and by the pattern of elution of extracted DNA from hydroxyapatite columns. These studies suggest that packaged intracellular melanin pigment has limited ability to protect cellular DNA from this type of photomediated injury