Putrescine

Putrescine (chemical formula (CH₂)₄(NH₂)₂) is a colorless solid that melts at roughly room temperature. Classified as a diamine, it shares with cadaverine the blame for the stench of rotting flesh, though it also turns up in other foul smells.

On an industrial scale, putrescine is made by hydrogenating succinonitrile. Researchers have also looked into biotechnological production from renewable feedstocks, describing a genetically engineered strain of *Escherichia coli* that churns out high concentrations of putrescine in a glucose mineral salts medium.

Biochemically, spermidine synthase combines putrescine with decarboxylated S-adenosyl methionine to form spermidine. Spermidine then teams up with another molecule of that same compound to become spermine. Healthy living cells produce small amounts of putrescine via ornithine decarboxylase. Two separate biological pathways, both starting from arginine, synthesize putrescine. In one, arginine becomes agmatine (catalyzed by arginine decarboxylase), then agmatine is turned into N-carbamoylputrescine by agmatine imino hydroxylase, and finally N-carbamoylputrescine is hydrolyzed to putrescine. In the other, arginine is converted to ornithine, and ornithine decarboxylase then transforms ornithine into putrescine. Through a series of metabolic intermediates—including N-acetylputrescine, γ-aminobutyraldehyde, N-acetyl-γ-aminobutyric acid, and others—and enzymes such as diamine oxidase, monoamine oxidase B, and aminobutyraldehyde dehydrogenase, putrescine can act as a minor biological precursor to GABA in the brain and elsewhere. In 2021, it was discovered that in the rodent striatum, MAO-B does not break down dopamine but instead participates in GABA synthesis, and that this GABA then inhibits dopaminergic neurons. MAO-B, via the putrescine pathway, importantly mediates GABA production in astrocytes across several brain regions, including the hippocampus, cerebellum, striatum, cerebral cortex, and substantia nigra pars compacta.

Putrescine occurs in every living organism. In plants, it is often the most abundant polyamine, with a well-documented role in development. Recent studies indicate it also helps plants respond to both biotic and abiotic stress; plants lacking putrescine see increased parasite and fungal populations. It functions as a cation substitute, an osmolyte, or a transport protein, and it regulates various surface proteins on cell membranes, mitochondria, and chloroplasts. Higher putrescine levels in mitochondria and chloroplasts boost ATP production, yet in some plants—like *Arabidopsis*—it can act as a developmental inhibitor, causing dwarfism and late flowering.

Soil fungi can also boost putrescine production in plants. *Piriformospora indica*, for example, promotes putrescine in *Arabidopsis* and tomato. A 2022 study found that this fungus enhanced root growth, and gas chromatography revealed higher putrescine levels in those roots. Inoculated plants showed excess arginine decarboxylase, an enzyme used in putrescine synthesis. One downstream effect of putrescine in root cells is auxin production. Adding putrescine as a fertilizer produced the same results as fungal inoculation in *Arabidopsis* and barley, though the evolutionary basis of this connection remains unclear.

In animals, putrescine contributes to bad breath and bacterial vaginosis. It also appears in semen and some microalgae, alongside spermine and spermidine.

Industrially, putrescine reacts with adipic acid to form nylon 46, sold by Envalior (formerly DSM) as Stanyl. Because of its role in putrefaction, it has been proposed as a biochemical marker for estimating time since death.

In agriculture, applying putrescine to plants lowers ethylene production. Pre-harvest treatment boosts resistance to high heat and drought. Post-harvest application to fruits—such as peaches, plums, cherries, tomatoes, and pears, as well as broccoli—delays ripening and extends shelf life. It slows deterioration in appearance (weight loss, rot, firmness), taste (soluble solids, acidity, organic acids), and nutrition (phenol and antioxidant content). A nanoparticle of putrescine coated with chitosan has been used as an edible coating on strawberries, yielding higher antioxidant capacity, enzyme activities, firmness, and total soluble solids, and extending post-harvest life.