The biosynthesis of spermidine. Part 3: the stereochemistry of the formation of the N-CH2 group in the biosynthesis of spermidine

Abstract

The stereochemistry of the formation of spermidine from butane-1,4-diamine and decarboxylated adenosylmethionine in Escherichia coli is shown to be inversion. That is to say, spermidine synthase mediates an S_N2 displacement in which the nucleophile is an amino group of butane-1,4-diamine, the carbon centre undergoing substitution with inversion is C-l of the 3-aminopropyl group of decarboxylated adenosylmethionine and the leaving group is 5-methylthioadenosine. This conclusion is based on the analysis, with the help of high-field ¹H n.m.r. spectroscopy, of the relative stereochemistries of derivatives of the [1′,2′-²H₂]spermidines derived from [3,4-²H₂] methionines of known relative configuration.