Mainigi K D, Sorof S
Proc Natl Acad Sci U S A. 1977 Jun;74(6):2293-6. doi: 10.1073/pnas.74.6.2293.
During carcinogenesis in rat liver by 3'-methyl-4-dimethylaminoazobenzene, the two moieties of the principal liver carcinogen-protein complex have considerably different turnover rates. With continued ingestion of the azocarcinogen by rats, the bound azo dye in the complex has a half-life of 2.5 +/- 0.25 (SD) days, while the protein moiety has a half-life of 8.7 +/- 1.6 days (probability of identity <0.001). In addition, the interaction of the azocarcinogen with the principal target protein in vivo appears to extend the half-life of the protein itself from 3.3 +/- 0.2 days in normal liver to 8.7 +/- 1.6 days (P < 0.001). The slowing of the turnover of the protein by the carcinogen appears to be readily reversible, since soon after the cessation of azocarcinogen feeding, the half-life of the protein returns to that of the target protein in normal liver. The considerable difference in turnover rates of the two moieties of the complex and the reversible effects of the carcinogen in slowing the turnover of the protein moiety suggest that the two moieties of the native azoprotein are noncovalently linked and that they have different biological activities. The native complex appears to contain azo dye in an activated state that is capable of yielding a reactive electrophile, because after protein denaturation the bound azo dye was previously found to have properties that are indicative of covalent linkage to the protein. The retardation in the biological turnover rate of the protein moiety, apparently resulting from interaction with azocarcinogen, is in agreement with the known ligand-induced stabilization in vitro and reduced rate of proteolytic degradation in vivo of other proteins that result from conformational change to a more compact configuration. Our evidence is consistent with the hypothesis that the principal liver carcinogen-protein complex contains hydrophobically bound activated azocarcinogen, whose specificity of reaction with critical macromolecule(s) in nuclei may be directed by the conformationally altered protein of an activated carcinogen-protein complex, i.e., a specific receptor protein containing activated azocarcinogen.
在大鼠肝脏由3'-甲基-4-二甲基氨基偶氮苯诱发癌变的过程中，主要的肝脏致癌物-蛋白质复合物的两个部分具有显著不同的周转率。随着大鼠持续摄入偶氮致癌物，复合物中结合的偶氮染料的半衰期为2.5±0.25（标准差）天，而蛋白质部分的半衰期为8.7±1.6天（同一性概率<0.001）。此外，偶氮致癌物在体内与主要靶蛋白的相互作用似乎将蛋白质本身的半衰期从正常肝脏中的3.3±0.2天延长至8.7±1.6天（P<0.001）。致癌物使蛋白质周转减慢的现象似乎很容易逆转，因为在停止喂食偶氮致癌物后不久，蛋白质的半衰期就恢复到正常肝脏中靶蛋白的半衰期。复合物两个部分周转率的显著差异以及致癌物对蛋白质部分周转减慢的可逆作用表明，天然偶氮蛋白的两个部分是非共价连接的，且它们具有不同的生物学活性。天然复合物似乎含有处于活化状态的偶氮染料，这种染料能够产生反应性亲电试剂，因为之前发现蛋白质变性后，结合的偶氮染料具有表明其与蛋白质共价连接的特性。蛋白质部分生物周转率的减慢显然是与偶氮致癌物相互作用的结果，这与已知的配体诱导体外稳定以及体内其他蛋白质因构象改变为更紧密构型而导致的蛋白水解降解速率降低相一致。我们的证据与以下假设一致：主要的肝脏致癌物-蛋白质复合物含有疏水结合的活化偶氮致癌物，其与细胞核中关键大分子的反应特异性可能由活化的致癌物-蛋白质复合物（即含有活化偶氮致癌物的特异性受体蛋白）的构象改变的蛋白质所引导。
