Non-enzymatic reactions are widespread and integral part of metabolism.
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Non-enzymatic metabolic reactions occur either spontaneously or small molecule catalyzed.
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They subdivide between broad/unspecific, and specific reactions that contribute to metabolism.
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Specific reactions occur both, exclusively non-enzymatically or parallel to enzymes.
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Non-enzymatic reactions affect drug design and network reconstruction.
Enzymes shape cellular metabolism, are regulated, fast, and for most cases specific. Enzymes do not however prevent the parallel occurrence of non-enzymatic reactions. Non-enzymatic reactions were important for the evolution of metabolic pathways, but are retained as part of the modern metabolic network. They divide into unspecific chemical reactivity and specific reactions that occur either exclusively non-enzymatically as part of the metabolic network, or in parallel to existing enzyme functions. Non-enzymatic reactions resemble catalytic mechanisms as found in all major enzyme classes and occur spontaneously, small molecule (e.g. metal-) catalyzed or light-induced. The frequent occurrence of non-enzymatic reactions impacts on stability and metabolic network structure, and has thus to be considered in the context of metabolic disease, network modeling, biotechnology and drug design.
