QBP3: Quantum tunnelling in enzyme action

Unlocking the Quantum Edge in Enzyme Catalysis: Navigating Energy Obstacles through Tunnelling:

Enzymes, essential catalysts driving countless vital chemical reactions within organisms, rely on the formation of an "enzyme-substrate complex" as a cornerstone of their exceptional efficiency. This complex serves as an impeccably engineered reaction chamber, bringing substrates into close proximity and ideal orientation for chemical transformations. Despite these optimal conditions, certain reactions encounter a challenge: an energy barrier separating reactants from products. Traditionally, particles must possess adequate kinetic energy to surmount this obstacle and progress the reaction. Enter the captivating realm of quantum mechanics.

Quantum mechanics introduces the concept of wave-particle duality, wherein particles can exhibit characteristics of both waves and particles. This has profound implications for enzyme catalysis, as it permits the phenomenon of quantum tunneling. The application of quantum biology principles to enzyme catalysis has opened up new avenues for exploring the fundamental mechanisms underlying these processes (Srivastava, 2019).

Figure source: https://pubs.rsc.org/en/journals/journalissues/cs#!recentarticles&adv

Tunneling Through the Wall: Quantum Trickery in Action

Imagine a symbolic barrier, representing the energy hurdle a reaction must overcome. According to classical mechanics, particles require ample energy to surmount this obstacle and reach the other side (products). However, quantum mechanics offers an alternative pathway - tunneling. Similar to a wave seemingly traversing a solid barrier, under specific conditions, a particle can probabilistically "tunnel" through the energy barrier during an enzyme-catalyzed reaction. Quantum tunneling allows particles to pass through energy barriers, enabling reactions to proceed more efficiently (Ball, 2011).

This quantum tunneling phenomenon is particularly significant for reactions involving lightweight particles like hydrogen atoms, prevalent in biological processes. Through harnessing tunneling, enzymes can markedly accelerate reaction rates, even for those considered sluggish by classical mechanics. By tunneling through these energy barriers, reactants can sidestep the conventional pathway and transition to the product state more efficiently. In enzyme-catalyzed reactions, such as hydrogen transfer, quantum tunneling has been observed to contribute significantly (Bahnson et al., 1997). Studies have shown that hydrogen tunneling in enzyme reactions can lead to complex kinetic isotope effects with temperature dependencies that challenge traditional rate theories (Glowacki et al., 2012). Experimental studies have emphasized the significance of quantum mechanical tunneling effects in enzyme kinetics, shedding light on the importance of understanding quantum phenomena in biological systems (Alhambra et al., 2000). In essence, enzymes have evolved to cultivate an environment that not only brings substrates together but also facilitates quantum tunneling. This remarkable harmony between molecular structure and quantum mechanics enables life to operate at an optimal pace, ensuring the seamless execution of myriad biochemical processes within our cells.

References:

Srivastava, R. (2019). The role of proton transfer on mutations. Frontiers in Chemistry, 7. https://doi.org/10.3389/fchem.2019.00536

Ball, P. (2011). Physics of life: the dawn of quantum biology. Nature, 474(7351), 272-274. https://doi.org/10.1038/474272a

Bahnson, B., Colby, T., Chin, J., Goldstein, B., & Klinman, J. (1997). A link between protein structure and enzyme catalyzed hydrogen tunneling. Proceedings of the National Academy of Sciences, 94(24), 12797-12802. https://doi.org/10.1073/pnas.94.24.12797

Glowacki, D., Harvey, J., & Mulholland, A. (2012). Taking ockham's razor to enzyme dynamics and catalysis. Nature Chemistry, 4(3), 169-176. https://doi.org/10.1038/nchem.1244

Alhambra, C., Corchado, J., Sánchez, M., Gao, J., & Truhlar, D. (2000). Quantum dynamics of hydride transfer in enzyme catalysis. Journal of the American Chemical Society, 122(34), 8197-8203. https://doi.org/10.1021/ja001476l