Smith B A, Gutmann H R, Springfield J R
Research Service, VA Medical Center, Minneapolis, MN 55417.
Biochem Pharmacol. 1989 Nov 15;38(22):3987-94. doi: 10.1016/0006-2952(89)90678-3.
Bovine serum albumin (BSA) catalyzes the o-rearrangement of the reactive electrophile, N-sulfooxy-2-acetylaminofluorene (NSF), a potential ultimate hepatocarcinogen in the rat, to the nonmutagenic sulfuric acid esters of 1- and 3-hydroxy-2-acetylaminofluorene. Conversion of NSF was proportional to BSA concentrations ranging from 0.25 to approximately 4 mg BSA/ml incubation mixture. At concentrations greater than or equal to 5 mg BSA/ml, approximately 90% of NSF was converted to the sulfuric acid esters of the o-amidofluorenols. Human serum albumin (HSA) likewise catalyzed the o-rearrangement of NSF. However, the catalytic activity of HSA was only approximately 50% of the activity of BSA. The catalytic effect of BSA was abolished by heat denaturation. However, it was not changed by dialysis or by anion exchange chromatography. These observations indicated that the catalytic effect requires intactness of the tertiary structure of BSA and is not due to a contaminant(s) of low or high molecular weight. There were no differences in the catalytic activity of three separate fractions of chromatographed BSA, suggesting that the catalytic activity is associated with the entire BSA molecule. In contrast to serum albumin, gamma-globulin (bovine or human) did not catalyze the o-rearrangement of NSF. The solvolytic degradation of NSF to 4-hydroxy-2-acetylaminofluorene, a major reaction in the absence of BSA, occurred only to a minor extent in the presence of BSA. These data indicated that the BSA-catalyzed o-rearrangement determines the rates of concurrent reactions involved in the degradation of NSF. BSA and HSA did not catalyze the o-rearrangement of N-acetoxy-2-acetylaminofluorene (N-OAC-2-AAF), the acetate ester of N-hydroxy-2-acetylaminofluorene (N-OH-2-AAF), to the acetic acid esters of the o-amidofluorenols. These findings suggest that the albumin-catalyzed o-rearrangement occurs preferentially with esters of fluorenylhydroxamic acids that readily ionize in aqueous media.
牛血清白蛋白（BSA）催化活性亲电试剂N-磺氧基-2-乙酰氨基芴（NSF，大鼠体内一种潜在的最终致癌物）发生邻位重排，生成1-和3-羟基-2-乙酰氨基芴的无致突变性硫酸酯。NSF的转化与BSA浓度成正比，孵育混合物中BSA浓度范围为0.25至约4mg/ml。当浓度大于或等于5mg BSA/ml时，约90%的NSF转化为邻氨基芴醇的硫酸酯。人血清白蛋白（HSA）同样催化NSF的邻位重排。然而，HSA的催化活性仅约为BSA活性的50%。BSA的催化作用通过热变性被消除。然而，透析或阴离子交换色谱并未改变其催化作用。这些观察结果表明，催化作用需要BSA三级结构的完整性，并非由于低分子量或高分子量的污染物所致。色谱分离得到的三个不同BSA组分的催化活性没有差异，这表明催化活性与整个BSA分子相关。与血清白蛋白不同，γ-球蛋白（牛或人）不催化NSF的邻位重排。在没有BSA的情况下，NSF向4-羟基-2-乙酰氨基芴的溶剂解降解是主要反应，但在有BSA存在时仅发生较小程度的降解。这些数据表明，BSA催化的邻位重排决定了NSF降解过程中并发反应的速率。BSA和HSA不催化N-乙酰氧基-2-乙酰氨基芴（N-OAC-2-AAF，N-羟基-2-乙酰氨基芴（N-OH-2-AAF）的乙酸酯）重排为邻氨基芴醇的乙酸酯。这些发现表明，白蛋白催化的邻位重排优先发生在芴基异羟肟酸酯上，这些酯在水性介质中容易电离。
