Spermidine  also known as spermidine trihydrochloride, is a kind of polyamine. Widely distributed in organisms, it is biosynthesized from butylenediamine and adenosine methionine. Spermidine inhibits neuronal synthetase, binds and precipitates DNA. It can also be used to purify DNA-binding proteins and stimulate T4 polynucleotide kinase activity.