Researchers from the Universities of Pennsylvania and Maine have discovered that, contrary to Newton’s third law of motion, not every action has an equal and opposite reaction. This finding, published in the journal Chem, could help understand how certain molecular interactions evolved in a pre-life world.

The team, led by Ayusman Sen, a professor of Chemistry at Penn State University, and R. Dean Astumian, a theoretical physicist at the University of Maine, has provided the first demonstration of the mechanism behind these interactions at the molecular level. Sen explains, We all have heard the phrase ‘every action has an equal and opposite reaction’ to describe Newton’s third law of motion, but every day we see examples that seem to violate it, especially in the behavior of large and small complex living systems where there is a constant input of energy.

The researchers studied two enzymes, kinases and phosphatases, which catalyze biochemical reactions. Kinases add a chemical modification to other molecules, while phosphatases remove these modifications. When the phosphatase was artificially immobilized, the kinase was attracted to it. However, when the kinase was immobilized, the phosphatase was repelled by it, demonstrating that an action does not always have an equal and opposite reaction.

Niladri Sekhar Mandal, a graduate student in chemical engineering at Penn State and one of the authors of the study, explains, Immobilizing one of the enzymes allows us to see how the other moves in relation to the first. The non-reciprocity we observe is not due to any external force but results from a combination of diffusion and kinetic asymmetries, which are properties of the enzymes.

Kinetic asymmetry describes the relative heights of the energy barriers that control the direction of a reaction in relation to a concentration gradient of the enzymes as they move in a molecular system. Sen states, The non-reciprocal interactions enabled by kinetic asymmetry also play a crucial role in allowing molecules to interact with each other. This may have played a critical role in the processes by which simple matter becomes complex, interacting in ways that ultimately led to life.

The researchers believe that understanding kinetic asymmetry could help elucidate the movement of molecules within cells and serve as a basis for designing synthetic molecular motors and pumps. Astumian adds, We are in the early stages of this work, but I see understanding kinetic asymmetry as a potential opportunity to understand how life evolved from simple molecules. Not only can it provide insights into the complexification of matter, but kinetic asymmetry can also be used in the design of molecular machines and associated technologies.


Pennsylvania State University | Niladri Sekhar Mandal, Ayusman Sen, et al., A molecular origin of non-reciprocal interactions between interacting active catalysts. Chem

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