Maltseva E L, Palmina N P, Burlakova E B
Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow.
Membr Cell Biol. 1998;12(2):251-68.
The effects of natural lipid-soluble antioxidant, alpha-tocopherol (alpha-TP), and the synthetic water-soluble antioxidant, phenosan potassium salt (Ph-K), in a broad range of concentrations down to ultralow doses (10(-4)-10(-20) M) on the activity of protein kinase C (PKC) have been studied. It was shown that alpha-TP is a potent inhibitor of the rabbit heart enzyme: the maximum extent of inhibition is 80%. The effects of alpha-TP on the main kinetic parameters of the PKC activity differ at the alpha-TP physiological (10(-4) M) and ultralow (10(-14) M) concentrations: at 10(-14) M, alpha-TP acts as an allosteric inhibitor with Hill's coefficient about 2 and doubles the PKC affinity to the substrate (histone H-1). It was concluded that alpha-TP is more efficient inhibitor at ultralow concentration. Ph-K added to normal (A7r5 rat vascular smooth muscle cells, VSMC) and tumor cells (Saos-2 human osteosarcoma) growing in a culture has been found to be a PKC superactivator. The maximum activation is 400-500%, which is more than two times as high as the effect of the best activator of this enzyme, phorbol ester (TPA). It was demonstrated that irrespective of the effector action (activation or inhibition), the dose-effect curves are of the bimodal type with two maxima at the high (or physiological) (10(-4)-10(-7) M) and ultralow (10(-14)-10(-19) M) concentrations of the antioxidants and the so-called "silence zones" between them, in which the effect of antioxidants is significantly reduced or absent (tumor cells). For the first time, these bimodal curves were observed at the enzyme level. The results obtained are discussed considering various hypotheses of the effect of ultralow doses of biologically active compounds and the PKC activity regulation in normal and tumor cells by the antioxidants.
研究了天然脂溶性抗氧化剂α-生育酚（α-TP）和合成水溶性抗氧化剂吩噻嗪钾盐（Ph-K）在低至超低剂量（10⁻⁴ - 10⁻²⁰ M）的广泛浓度范围内对蛋白激酶C（PKC）活性的影响。结果表明，α-TP是兔心脏酶的有效抑制剂：最大抑制程度为80%。α-TP对PKC活性的主要动力学参数的影响在α-TP的生理浓度（10⁻⁴ M）和超低浓度（10⁻¹⁴ M）下有所不同：在10⁻¹⁴ M时，α-TP作为变构抑制剂，希尔系数约为2，并使PKC对底物（组蛋白H-1）的亲和力增加一倍。得出结论，α-TP在超低浓度下是更有效的抑制剂。已发现添加到培养中的正常（A7r5大鼠血管平滑肌细胞，VSMC）和肿瘤细胞（Saos-2人骨肉瘤）中的Ph-K是PKC的超激活剂。最大激活率为400 - 500%，比该酶最佳激活剂佛波酯（TPA）的效果高出两倍多。结果表明，无论效应器作用是激活还是抑制，剂量-效应曲线均为双峰型，在抗氧化剂的高（或生理）浓度（10⁻⁴ - 10⁻⁷ M）和超低浓度（10⁻¹⁴ - 10⁻¹⁹ M）处有两个最大值，且在它们之间存在所谓的“沉默区”，其中抗氧化剂的作用显著降低或不存在（肿瘤细胞）。首次在酶水平上观察到这些双峰曲线。结合超低剂量生物活性化合物的作用以及抗氧化剂对正常和肿瘤细胞中PKC活性调节的各种假设，对所得结果进行了讨论。
