title: Inhibition of mammalian DNA polymerases by hematoporphyrin derivative and photoradiation.
abstract: Hematoporphyrin derivative (HPD) plus photoradiation caused the inactivation of DNA polymerases from calf thymus and R3230AC rat mammary tumor. Photosensitization of purified DNA polymerase-alpha as well as two forms of DNA polymerase-delta (I and II) from calf thymus were evaluated. Although all polymerase enzyme forms were inactivated at 70 micrograms HPD/ml, DNA polymerase-delta II was the most sensitive, displaying a 90% inactivation under conditions that did not cause significant inactivation of the other polymerase forms. Unlike DNA polymerase-alpha, the delta-forms have an associated 3'- to 5'-exonuclease activity. The exonuclease associated with DNA polymerase-delta II was uniquely sensitive to a low level of HPD and light exposure. DNA polymerase-delta II can be distinguished from other polymerase forms in cell extracts by its relative insensitivity to the polymerase inhibitor N2-(p-n-butylphenyl)deoxyadenosine 5'-triphosphate. In cytosols prepared from calf thymus and R3230AC rat mammary tumors, DNA polymerase-delta II was preferentially inhibited by HPD plus light. Furthermore, in experiments in which tumor-bearing rats were administered HPD prior to preparation of tumor cytosols, DNA polymerase-delta II was specifically inactivated by exposure to light. These results are discussed in view of their possible role in cancer therapy, and the potential use of HPD as a specific inhibitory agent of DNA polymerase-delta II is suggested.
mesh_terms: D000818:Animals; D002417:Cattle; D003600:Cytosol / Q000201:enzymology; D004258:DNA Polymerase III; D004259:DNA-Directed DNA Polymerase / Q000528:radiation effects; D006414:Hematoporphyrin Photoradiation; D008325:Mammary Neoplasms, Experimental / Q000201:enzymology; D019384:Nucleic Acid Synthesis Inhibitors; D010778:Photochemotherapy; D051381:Rats; D013950:Thymus Gland / Q000201:enzymology
chemical_list: D019384:Nucleic Acid Synthesis Inhibitors; D004258:DNA Polymerase III; D004259:DNA-Directed DNA Polymerase