Measurement of thermal contribution to photoreceptor sensitivity
Measurement of thermal contribution to photoreceptor sensitivity
复制标题
测量热对感光器敏感性的贡献
作者：
A. Koskelainen;P. Ala;N. Fyhrquist;K. Donner
激活视色素分子以启动光转导需要最低能量 Ea，该能量不必完全来自光子，但可以通过热量补充。理论预测，极长波长下的吸光度随着具有足够热能补充的分子分数而下降，并且 Ea 与颜料的最大吸光度 (λmax) 的波长成反比。与第一个预测一致，变暖增加了对长波长的相对视觉敏感性。在这里，我们测量了具有不同色素的两栖动物感光器中的这种效应，以估计 Ea（参考文献 2、5、6、7），并通过实验测试 Ea 和 λmax 之间反比关系的预测。对于成年青蛙视网膜中的视杆细胞和“红色”视锥细胞，我们发现所涉及的两种色素之间的 Ea 没有显着差异，尽管它们的 λmax 值非常不同。我们还测定了蟾蜍视网膜视杆中视紫红质的 Ea（光谱与青蛙视紫红质相似，但氨基酸序列不同），并发现它明显更高。此外，我们还估计了两种色素的 Ea，其 λmax 差异仅归因于发色团差异（A1 和 A2 色素，在成年和幼虫青蛙锥体中）。这里 A2 的 Ea 低于 A1。我们的结果反驳了 λmax 和 Ea 之间存在必然关系的观点，但表明 A1 → A2 发色团取代会降低 Ea。
Activation of a visual pigment molecule to initiate phototransduction requires a minimum energy, Ea, that need not be wholly derived from a photon, but may be supplemented by heat. Theory predicts that absorbance at very long wavelengths declines with the fraction of molecules that have a sufficient complement of thermal energy, and that Ea is inversely related to the wavelength of maximum absorbance (λmax) of the pigment. Consistent with the first of these predictions, warming increases relative visual sensitivity to long wavelengths. Here we measure this effect in amphibian photoreceptors with different pigments to estimate Ea (refs 2, 5,6,7) and test experimentally the predictions of an inverse relation between Ea and λmax. For rods and ‘red’ cones in the adult frog retina, we find no significant difference in Ea between the two pigments involved, although their λmax values are very different. We also determined Ea for the rhodopsin in toad retinal rods—spectrally similar to frog rhodopsin but differing in amino-acid sequence—and found that it was significantly higher. In addition, we estimated Ea for two pigments whose λmax difference was due only to a chromophore difference (A1 and A2 pigment, in adult and larval frog cones). Here Ea for A2 was lower than for A1. Our results refute the idea of a necessary relation between λmax and Ea, but show that the A1 → A2 chromophore substitution decreases Ea.
来自三种青蛙和蟾蜍物种的视紫红质：序列和功能比较。
DOI：
10.1006/exer.1997.0430
发表时间：
1998
期刊：
Experimental eye research.
影响因子：
--
作者：
Fyhrquist,N;Donner,K;Hargrave,PA;McDowell,JH;Popp,MP;Smith,WC
通讯作者：
Smith,WC
影响因子：
5.5
作者：
SCHNAPF, JL;NUNN, BJ;BAYLOR, DA
通讯作者：
BAYLOR, DA