The Xenoreactome: Where Foreign Chemistry Becomes Biological Organization

Abstract Biological systems can perform chemistry beyond their evolved reaction networks, but a reaction that is chemically possible does not necessarily occur in an intact system. I define the xenoreactome as the state- and reference-dependent network through which foreign chemistry enters a biological or cell-like system, is transformed and propagated, and is ultimately cleared or retained. The concept focuses on the factors that determine whether foreign chemistry is realized, including transport, localization, physiological state, downstream transfer, and clearance. Xenoreactomes may remain entirely molecular, carry non-native chemical or elemental features through existing biological machinery, or support reaction sequences with no direct biological counterpart, such as sustained free-radical vinyl polymerization. In some cases, xenochemical products can also accumulate sufficiently to form polymers, condensed phases, or other material states. For these systems, I introduce a simple quantitative criterion that relates xenochemical production and persistence to the threshold required for material formation. The xenoreactome provides a framework for asking which foreign chemistry biological systems can actually support, how far it propagates, and what ultimately happens to its products.