Jensen D E, Lotlikar P D, Magee P N
Carcinogenesis. 1981;2(4):349-54. doi: 10.1093/carcin/2.4.349.
Utilizing the microsomal fraction isolated from hamster liver we have identified and quantitated some of the alkylation lesions introduced into exogenous DNA as a consequence of the microsomally-mediated decomposition of 14C-labeled dimethylnitrosamine and have established correlations between this DNA alkylation and formaldehyde formation. The yield of radiolabeled formaldehyde was assessed by the formaldemethone-precipitation method and the yields of the major methylated purines present in a mild acid hydrolysate of modified DNA determined using cation exchange high pressure liquid chromatography techniques. We found 7-methylguanine, 3-methyladenine and O(6)-methylguanine in our DNA hydrolysates in the same relative proportions as observed in DNA isolated from similar incubation mixtures containing methylnitrosourea as the methylating compound. The rate of DNA methylation was observed to correlate well with the rate of formaldehyde formation and, even thought the absolute formaldehyde and DNA methylation yields varied in experiments done on different days, the relative yields were found to be consistent. Both processes were NADPH dependent, both were inhibited by carbon monoxide, and both were equally sensitive to chemical agents which appear to interfere with dimethylnitrosamine metabolism in vivo.
利用从仓鼠肝脏分离得到的微粒体部分，我们已经鉴定并定量了由于微粒体介导的14C标记的二甲基亚硝胺分解而引入到外源DNA中的一些烷基化损伤，并建立了这种DNA烷基化与甲醛形成之间的相关性。通过甲醛肟沉淀法评估放射性标记甲醛的产量，并使用阳离子交换高压液相色谱技术测定修饰DNA的温和酸水解产物中主要甲基化嘌呤的产量。我们在DNA水解产物中发现了7-甲基鸟嘌呤、3-甲基腺嘌呤和O(6)-甲基鸟嘌呤，其相对比例与从含有甲基亚硝基脲作为甲基化化合物的类似孵育混合物中分离得到的DNA中观察到的比例相同。观察到DNA甲基化速率与甲醛形成速率密切相关，并且，即使在不同日期进行的实验中绝对甲醛和DNA甲基化产量有所不同，但相对产量是一致的。这两个过程都依赖于NADPH，都受到一氧化碳的抑制，并且对似乎在体内干扰二甲基亚硝胺代谢的化学试剂同样敏感。
