Enantioselective N-Acetylation of N-Desisopropylpropranolol by Rat Liver Acetyltransferase.
作者:Xiuzhong WU、Yoko ONO、Atsuko NODA、Hiroshi NODA
DOI:10.1248/bpb.21.1361
日期:——
The enantioselective N-acetylation of N-desisopropylpropranolol (NDP), one of the main metabolites of propranolol (PL), by rat liver acetyltransferase (AT), was investigated. R(+)-NDP or S(-)-NDP was used as a substrate at concentrations ranging from 10 to 200 μM. The cytosol fraction of a rat liver containing 3.93 mg protein/ml served as the source of AT. For 1-amino-3-(1-naphthyloxy)-2-propanol (AcNDP) formation from R(+)-NDP or S(-)-NDP in the presence of infinite AcCoA (250 μM), the Km value was calculated to be 67.5 or 62.4 μM, and the Vmax value was 0.462 or 0.205 nmol/min/mg protein. Based on these findings, the enantioselective N-acetylation of NDP was proved, i.e., AcNDP formation from R(+)-NDP was found to take place more easily than that from S(-)-NDP. Furthermore, AcNDP formation from NDP was competitively inhibited by the exogenous arylamine, p-aminobenzoic acid (PABA), which is well-known to be a typical substrate of AT. The presence of enantioselective inhibition for AcNDP formation was thus confirmed based on the Ki values, 440 μM in the case of R(+)-NDP and 250 μM in the case of S(-)-NDP, respectively, i.e. two-fold enantioselective inhibition was demonstrated based on the Ki values in S(-)-enantiomer incomparison with R(+)-enantiomer.
研究了大鼠肝脏乙酰转移酶(AT)对普萘洛尔(PL)的主要代谢产物之一 N-异丙基普萘洛尔(NDP)的对映选择性 N-乙酰化。以 R(+)-NDP 或 S(-)-NDP 为底物,浓度为 10 至 200 μM。含有 3.93 毫克蛋白质/毫升的大鼠肝脏细胞质部分是 AT 的来源。在无限量 AcCoA(250 μM)存在下,由 R(+)-NDP 或 S(-)-NDP 生成 1-氨基-3-(1-萘氧基)-2-丙醇(AcNDP)时,Km 值分别为 67.5 或 62.4 μM,Vmax 值分别为 0.462 或 0.205 nmol/min/mg。基于这些发现,证明了 NDP 的对映选择性 N-乙酰化,即 R(+)-NDP 比 S(-)-NDP 更容易形成 AcNDP。此外,由 NDP 生成 AcNDP 会受到外源芳基胺对氨基苯甲酸(PABA)的竞争性抑制,而 PABA 是众所周知的 AT 的典型底物。R(+)-NDP 的 Ki 值为 440 μM,S(-)-NDP 的 Ki 值为 250 μM,即与 R(+)-enantiomer 相比,S(-)-enantiomer 的 Ki 值为对映体选择性抑制的两倍。