CHARACTERISTICS OF CHEMICAL-BINDING TO ALPHA-2U-GLOBULIN INVITRO - EVALUATING STRUCTURE-ACTIVITY-RELATIONSHIPS

α2u-Globulin (α2u) has been shown to accumulate in the kidneys of male rats treated with 2,2,4-trimethylpentane (TMP). 2,4,4-Trimethyl-2-pentanol (TMP-2-OH), a metabolite of TMP, is found reversibly bound to α2u isolated from the kidneys of these treated rats. The objectives of the following study were to characterize the ability of [3H]TMP-2-OH to bind to α2u in vitro and to determine whether other compounds that cause this protein to accumulate have the same binding characteristics. Although compounds that have been shown to cause the accumulation of α2u in male rat kidneys compete in vitro with [3H]TMP-2-OH for binding to α2u, they do so to varying degrees. The binding affinity (Kd of the [3H]TMP-2-OH-α2u complex was calculated to be on the order of 10-7, m. The inhibition constant values (Ki) determined for d-limonene, 1,4-dichlorobenzene, and 2,5-dichlorophenol were all in the range 10-4, m, whereas the Ki values for isophorone, 2,4,4- or 2,2,4-trimethyl-1-pentanol, and d-limonene oxide were determined to be in the range 10-6 and 10-7, m, respectively. TMP and 2,4,4-and 2,2,4-trimethylpentanoic acid did not compete for binding. This suggests that other factors, besides binding, are involved in the accumulation of α2u. In this study the ability of a chemical to bind to α2u was used as a measure of biological activity to assess structure-activity relationships among the chemicals tested and known to cause the accumulation of α2u. The results so far suggest that binding is dependent on both hydrophobic interactions and hydrogen bonding. © 1991.