Cadaverine and putrescine are organic compounds widely recognized for their strong, unpleasant odors. These molecules are diamines, characterized by having two amino functional groups. They are infamous for being major components of the volatile compounds that create the characteristic smell of decaying flesh. Despite this association with spoilage, their presence is not limited to putrefying matter. Understanding these molecules requires exploring their biochemical origins and varied roles in living biological systems.
The Biochemical Origin of Cadaverine and Putrescine
The primary mechanism for the formation of cadaverine and putrescine in decaying organic matter is microbial activity, known as putrefaction. Bacteria and other microorganisms break down proteins in animal and plant tissues after death. This breakdown involves decarboxylation, a specific chemical reaction catalyzed by bacterial enzymes.
Cadaverine is synthesized from the decarboxylation of the amino acid lysine. This conversion removes a carboxyl group, resulting in the five-carbon diamine. Putrescine is generated through the decarboxylation of the amino acid ornithine, and sometimes arginine. Putrescine is a four-carbon diamine, chemically distinct from cadaverine but sharing a similar foul odor.
Bacteria utilize decarboxylation to buffer the pH of their environment. By removing the acidic carboxyl group from the amino acid, they produce the more basic amine, neutralizing an increasingly acidic environment. The resulting accumulation of these volatile diamines produces the odor that indicates advanced biological breakdown.
Essential Roles in Living Organisms
Despite their association with decay, both cadaverine and putrescine are naturally present in small amounts within healthy living cells, including those of humans, animals, and plants. In living systems, putrescine acts as the starting point for the biosynthesis of polyamines, such as spermidine and spermine. These polyamines are small, positively charged molecules necessary for fundamental cellular processes.
Polyamines play a structural part in stabilizing the genetic material by interacting with the negatively charged backbone of DNA and RNA. This interaction helps regulate gene expression, enables accurate DNA replication, and is necessary for normal cell proliferation and growth. Putrescine is synthesized endogenously in healthy cells through pathways involving ornithine decarboxylase.
Cadaverine is also found in trace amounts in living organisms and is considered a polyamine, though its functional role is less pronounced than putrescine. In some plants, cadaverine is synthesized from lysine and contributes to growth, development, and stress responses. The presence of these diamines in human urine or breath is a normal byproduct of metabolism and the activity of the gut microbiome.
Indicators of Decay and Food Spoilage
The buildup of cadaverine and putrescine makes them effective markers for the freshness and safety of perishable goods. These compounds are classified as biogenic amines, and their concentrations are directly proportional to bacterial contamination and spoilage in protein-rich foods. This measurement is frequently used in commercial quality control, especially for fish and meat products, where high levels signal spoilage.
Measuring the total concentration of these biogenic amines provides a more objective assessment of food quality than traditional sensory methods. For instance, cadaverine levels can become particularly high in fish during storage because fish proteins are rich in the precursor amino acid lysine. The detection of these amines at high concentrations indicates that microbial activity has progressed to a point that often precedes the presence of harmful pathogens.
Beyond food safety, the predictable increase of these diamines after death has established their role in forensic science. Forensic investigators analyze the concentration of cadaverine and putrescine in tissues to help estimate the Post-Mortem Interval (PMI). Studies have shown a linear correlation between the increasing levels of these compounds and the progression of the PMI. Putrescine, in particular, has been found to be a slightly more accurate biomarker than cadaverine for estimating the time since death in brain tissue.