Spermidine is a naturally occurring polyamine compound found widely across various organisms. It is a triamine, meaning it possesses three amino groups, which contribute to its diverse roles within living systems. Spermidine is present in ribosomes and living tissues, where it participates in metabolic functions. It is fundamental for cellular well-being and balance.
The Biological Synthesis of Spermidine
The creation of spermidine within living organisms follows a specific biochemical pathway, primarily starting from the amino acid ornithine. Ornithine is converted into putrescine through the action of the enzyme ornithine decarboxylase (ODC). This step is a key regulatory point in the production of polyamines. Once putrescine is formed, it serves as a direct precursor for spermidine.
Spermidine synthase then catalyzes the transfer of an aminopropyl group to putrescine. This aminopropyl group is donated by a modified form of S-adenosylmethionine (SAM), decarboxylated S-adenosylmethionine (dcSAM). SAM is first decarboxylated by S-adenosylmethionine decarboxylase (SAMDC) to produce dcSAM. Spermidine synthase then uses putrescine and dcSAM to form spermidine.
The reaction facilitated by spermidine synthase is highly specific, preferring putrescine as the amine acceptor. This ordered enzymatic process ensures the precise production of spermidine, which is important for cellular activities. The regulation of enzymes like ornithine decarboxylase can influence intracellular spermidine levels.
Spermidine’s Presence in Nature and Diet
Spermidine is found throughout the natural world, present in a wide array of living organisms, including plants, animals, and microorganisms. Its ubiquitous presence highlights its importance across biological kingdoms. Many common foods serve as dietary sources of spermidine, allowing humans to acquire this compound through their diet.
Significant dietary sources of spermidine include wheat germ, a rich source, containing approximately 243 mg per kilogram. Aged cheeses, such as Parmesan and blue cheese, also contain notable amounts (1.5-3 mg per 100g). Soybeans and their fermented products like natto are rich plant-based sources, with natto containing high levels (65-340 mg per kilogram).
Mushrooms, particularly varieties like Black Shimeji and shiitake, provide over 120 mg per kilogram and about 67 mg per kilogram, respectively. Other vegetables and legumes, such as green peas (around 50 mg/kg), broccoli (about 32.4 mg/kg), and lentils, are also contributors to dietary spermidine intake. Beyond direct dietary intake, the human gut microbiota also contributes to the body’s spermidine levels by synthesizing it from precursors like putrescine or arginine. This internal production, alongside dietary consumption, influences spermidine availability.