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|Section2= |Section3= |Section4= }} Spermidine is a polyamine compound () found in ribosomes and living tissues, and having various metabolic functions within organisms. It was originally isolated from semen.〔(American Heritage Dictionary ) Retrieved 2014-11-18.〕 ==Function== Polyamines, such as spermidine, are polycationic aliphatic amines and are multifunctional. They serve vital roles in cell survival. Spermidine synthase (SPDS) catalyzes the formation of spermidine from putrescine. Spermidine is a precursor to further polyamines, such as spermine and its structural isomer thermospermine. Spermidine synchronizes an array of biological processes (such as Ca2+, Na+, K+ -ATPase) thus maintaining membrane potential and controlling intracellular pH and volume. Spermidine regulates biological processes, such as Ca2+ influx by glutamatergic N-methyl-d-aspartate receptor (NMDA receptor), which has been associated with nitric oxide synthase (NOS) and cGMP/PKG pathway activation and a decrease of Na+,K+-ATPase activity in cerebral cortex synaptosomes. Spermidine is a longevity agent in mammals due to various mechanisms of action, which are just beginning to be understood. Autophagy is the main mechanism at the molecular level, but evidence has been found for other mechanisms, including inflammation reduction, lipid metabolism, and regulation of cell growth, proliferation and death. Spermidine is known to regulate plant growth, assisting the ''in vitro'' process of transcribing RNA, and inhibition of NOS. Also, spermidine is a precursor to other polyamines, such as spermine and thermospermine, some of which contribute to tolerance against drought and salinity in plants. Spermidine has been tested and discovered to encourage hair shaft elongation and lengthen hair growth. Spermidine has also been found to “upregulate expression of the epithelial stem cell-associated keratins K15 and K19, and dose-dependently modulated K15 promoter activity ''in situ'' and the colony forming efficiency, proliferation and K15 expression of isolated human K15-GFP+ cells ''in vitro''.” 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「spermidine」の詳細全文を読む スポンサード リンク
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