Partial purification and characterization of spermine synthase from rat brain

Abstract

Spermine synthase, the enzyme catalyzing the formation of spermine from spermidine and 5′-ndeoxy-5′- S-(3-methylthiopropylamine)sulphonium adenosine (decarboxylated S-adenosylmethionine) has been purified more than 100-fold from rat brain cytosol fraction. Spermine synthase activity can be resolved from the other polyamine-synthesizing enzyme activities, i.e. from S-adenosylmethionine decarboxylase and spermidine synthase activities, by a single chromatography run on DEAE-cellulose. The purified spermine synthase, free of any S-adenosylmethionine decarboxylase or spermidine synthase activity, showed a broad pH optimum between 7.5 and 8.1 and an acidic isoelectric point at pH 5.0. Spermine synthase appeared to have a high affinity for decarboxylated S-adenosylmethionine, the apparent K m value being below 0.005 mM. The K m for spermidine was 0.07 mM. Putrescine was shown to be a competitive inhibitor with respect to spermidine, and spermine, the product of the reaction, was also inhibitory. No metal or other cofactor requirements for spermine synthase were found.