Matsuki H, Suzuki A, Kamaya H, Ueda I
Department of Anesthesia, Anesthesia Service 112A, DVA Medical Center, and University of Utah School of Medicine, 500 Foothill Blvd. , Salt Lake City, UT 84148, USA.
Biochim Biophys Acta. 1999 Jan 4;1426(1):143-50. doi: 10.1016/s0304-4165(98)00148-2.
Firefly luciferase emits a burst of light when the substrates luciferin and ATP are mixed in the presence of oxygen. We (I. Ueda, A. Suzuki, Biophys. J. 75 (1998) 1052-1057) reported that long-chain fatty acids are specific inhibitors of firefly luciferase in competition with luciferin in microM ranges. They increased the thermal transition temperature. In contrast, 1-alkanols of the same carbon chain length inhibited the enzyme non-competitively in mM ranges and decreased the transition temperature. The present study showed that the action of fatty acids switched from specific to non-specific when the carbon chain length was reduced below C8 (octanoate). The fatty acids longer than C10 inhibited the enzyme in microM ranges whereas those shorter than C8 required mM ranges to inhibit it. The longer fatty acids increased whereas shorter fatty acids decreased the transition temperature. The Hill coefficients of longer chain bindings were less than one whereas those of shorter chain were more than one. The shorter fatty acids interacted with the enzyme cooperatively at multiple sites. Binding of the longer fatty acids is limited. Fatty acids longer than C10 are high-affinity specific binders and followed Koshland's induced-fit model. Those shorter than C8 are low-affinity non-specific denaturants and followed Eyring's rate process model. These results contradict the general consensus that the size of the receptor cavity discriminates specific binders.
当底物荧光素和ATP在氧气存在的情况下混合时，萤火虫荧光素酶会发出一阵光。我们（上田一、铃木明，《生物物理杂志》75 (1998) 1052 - 1057）报道，长链脂肪酸是萤火虫荧光素酶的特异性抑制剂，在微摩尔范围内与荧光素竞争。它们提高了热转变温度。相比之下，相同碳链长度的1 - 链烷醇在毫摩尔范围内非竞争性地抑制该酶，并降低转变温度。本研究表明，当碳链长度缩短至C8（辛酸）以下时，脂肪酸的作用从特异性转变为非特异性。碳链长度大于C10的脂肪酸在微摩尔范围内抑制该酶，而碳链长度小于C8的脂肪酸则需要毫摩尔范围才能抑制它。较长的脂肪酸会提高而较短的脂肪酸会降低转变温度。较长链结合的希尔系数小于1，而较短链的希尔系数大于1。较短的脂肪酸在多个位点与酶协同相互作用。较长脂肪酸的结合是有限的。碳链长度大于C10的脂肪酸是高亲和力特异性结合剂，遵循科什兰德的诱导契合模型。那些碳链长度小于C8的脂肪酸是低亲和力非特异性变性剂，遵循艾林的速率过程模型。这些结果与受体腔大小区分特异性结合剂的普遍共识相矛盾。
