血卟啉衍生物（HPD）加光照对无细胞体系DNA合成的抑制作用

EFFECT OF HEMATOPORPHYRIN DERIVATlVE(HPD)PLUS LIGHT ON DNA SYNTHESIS IN VITRO

本文从腹水型肝癌细胞部分纯化了依赖于ＤＮＡ的ＤＮＡ聚合酶。，以热变性的小牛胸腺ＤＮＡ为模板，观察了ＨＰＤ的光敏效应对这－ＤＮＡ合成体系的影响。结果表明，单独的ＨＰＤ或光照对无细胞体系ＤＮＡ合成无影响；而既用ＨＰＤ处理，又经光照后的ＤＮＡ合成系统表现出明显的抑制作用。此抑制作用呈显著的剂量和时间的依赖效应关系．ＨＰＤ的光敏反应与ＤＮＡ模板非竞争性地作用于酶。增加模板量不能使抑制作用逆转：而增加酶量可使抑制作用部分逆转。四种脱氧核苷三磷酸与ＨＰＤ预保温未见抑制作用；酶与ＨＰＤ预保温后抑制率比对照组增加两倍；而酶和ＤＮＡ一起与之预保温后抑制率则增加近４倍。捉示ＨＰＡ的光敏效应是既抑制了酶活性又破坏了ＤＮＡ模板的结构和功能，从而发挥最大的抑制作用。

The effect of HPD plus light on cell-free DNA synthesis catalyzed bypartially purified DNA-dependent DNA polymeras ea from hepatoma ceIls was studied by us-ing calf thymus DNA of thermal denaturation as template。 The results showed that the DNAsynthesis system w as markedly inhibited by toth HPD and light treatment, and the degree ofinhibition was dependent on the HPD concentration and exposure time。 No changes could beobserved when either HPD or light irradiation was used alone .This inhibition could not bereversed by in creasing DNA concentration but could be abolished by increasing enzyme con-centmtion.Preincube tion of HPD with the enzyme preduced stronger inhibition than that withdNTPs when exposed to lighl However, the strongest inhibition would be caused after prei-ncubetion of HPD with the enzyme and DNA treether under light activation。 These resultssuggest that the enzyme may be the major target for photosensitizing effect and HPD phot-osensitization not only suppre ased the enzyme activity but also destroved the structure andfunction of DNA template, which led to the strongest inhibition of DNA synthesis