High sensitivity of scotopic vision (vision in dim light conditions) is achieved by the rods’ low background noise, which is attributed to a much lower thermal activation rate () of rhodopsin compared with cone pigments. Frogs and nocturnal geckos uniquely possess atypical rods containing noncanonical cone pigments that exhibit low , mimicking rhodopsin. Here, we investigated the convergent mechanism underlying the low of rhodopsins and noncanonical cone pigments. Our biochemical analysis revealed that the of canonical cone pigments depends on their absorption maximum (λ). However, rhodopsin and noncanonical cone pigments showed a substantially lower than predicted from the λ dependency. Given that the λ is inversely proportional to the activation energy of the pigments in the Hinshelwood distribution-based model, our findings suggest that rhodopsin and noncanonical cone pigments have convergently acquired low frequency of spontaneous-activation attempts, including thermal fluctuations of the protein moiety, in the molecular evolutionary processes from canonical cone pigments, which contributes to highly sensitive scotopic vision.

中文翻译：

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脊椎动物暗视觉获得的收敛机制

视杆细胞的低背景噪声实现了高灵敏度的暗视觉（弱光条件下的视力），这归因于与视锥细胞色素相比，视紫红质的热激活率 () 低得多。青蛙和夜间活动的壁虎拥有独特的非典型视杆细胞，其中含有非典型视锥细胞色素，表现出低水平、模仿视紫红质。在这里，我们研究了视紫红质和非典型视锥色素低水平背后的收敛机制。我们的生化分析表明，标准锥体色素的吸收最大值 (λ) 取决于它们。然而，视紫红质和非标准视锥细胞色素的表现明显低于根据 λ 依赖性预测的值。鉴于基于 Hinshelwood 分布的模型中 λ 与色素的活化能成反比，我们的研究结果表明，视紫红质和非规范视锥色素已经收敛地获得了低频的自发激活尝试，包括蛋白质部分的热波动，典型视锥色素的分子进化过程，有助于高度敏感的暗视视觉。