The discovery of naturally occurring B₁₂-depedent photoreceptors has allowed for applications of cobalamins (Cbls) in optogenetics and synthetic biology to emerge. However, theoretical investigations of the complex mechanisms of these systems have been lacking. Adenosylcobalamin (AdoCbl)-dependent photoreceptor, CarH, is one example and it relies on daylight to perform its catalytic function. Typically, in enzymes employing AdoCbl as their cofactor, the Co-C_5′ bond activation and cleavage is triggered by substrate binding. The cleavage of the Co-C_5′ bond is homolytic resulting in radical pair formation. However, in CarH, this bond is instead activated by light. To explore this peculiarity, the ground and first excited state potential energy surfaces (PESs) were constructed using the quantum mechanics/molecular mechanics (QM/MM) framework and compared with other AdoCbl-dependent enzymes. QM/MM results indicate that CarH is photolytically active as a result of the AdoCbl dual role, acting as a radical generator and as a substrate. Photo-cleavage of the Co-C_5′ bond and subsequent H-atom abstraction is possible because of the specific orientation of the H-C_4′ bond with respect to the Co(II) center. Comparison with other AdoCbl-dependent enzymes indicate that the protein environment in the CarH active center alters the photochemistry of AdoCbl by controlling the stereochemistry of the ribose moiety.

天然存在的依赖B _12的感光器的发现使得钴胺素（Cbls）在光遗传学和合成生物学中的应用得以出现。但是，缺乏对这些系统的复杂机制的理论研究。依赖于腺苷钴胺素（AdoCbl）的感光体CarH就是一个例子，它依靠日光来完成其催化功能。通常，在采用AdoCbl作为其辅因子的酶中，Co-C _5'键的活化和裂解是通过底物结合来触发的。Co-C _5'的裂解键是均溶的，导致自由基对的形成。但是，在CarH中，该键被光激活。为了探索这种特殊性，使用量子力学/分子力学（QM / MM）框架构造了基态和第一激发态势能面（PES），并将其与其他依赖AdoCbl的酶进行了比较。QM / MM结果表明，由于AdoCbl双重作用，CarH具有光解活性，可充当自由基产生剂和底物。由于HC _4'的特定方向，可能发生Co-C _5'键的光裂解和随后的H原子抽象相对于Co（II）中心的键。与其他依赖AdoCbl的酶的比较表明，CarH活性中心中的蛋白质环境通过控制核糖部分的立体化学来改变AdoCbl的光化学。